BEVA 371 AND ITS USE AS AN ADHESIVE FOR SKIN AND LEATHER REPAIRS: BACKGROUND AND A REVIEW OF TREATMENTS
LISA KRONTHAL, JUDITH LEVINSON, CAROLE DIGNARD, ESTHER CHAO, & JANE DOWN
ABSTRACT—Since its introduction in the 1970s, the use of BEVA 371 (solution and film) has expanded from the field of paintings conservation into textiles and objects conservation. During the development of BEVA 371 solution, initial testing was conducted to determine its strength, compatibility, effectiveness, reversibility, and aging qualities in accordance with its intended use in paintings conservation. Its use beyond the treatment of paintings is widespread; however, no comprehensive testing has been accomplished for these specific uses. This article presents a summary of published analyses and testing of BEVA 371 and a review of skin and leather treatments using BEVA 371 solution and film, focusing on the versatility of the adhesive and the variables that affect bond strength. Also presented is a historic overview of the uses of BEVA 371 solution and film on skin and leather. The condition of a group of skin objects that were treated with these BEVA products at the American Museum of Natural History (AMNH) from the mid-1980s through the 1990s was assessed.
TITRE—Le BEVA 371 et son utilisation en tant qu'adh�sif pour r�parer les peaux et les cuirs: revue de ses propri�t�s et suivi des traitements. R�SUM�— Depuis que le BEVA 371 (en solution et en film) a �t� introduit dans les ann�es 1970, son emploi, qui �tait � l'origine l'apanage du domaine de la restauration des peintures, s'est �largi � ceux des textiles et des objets. Lorsque le BEVA 371 en solution fut d�velopp�, il fut l'objet de tests pour d�terminer sa r�sistance, sa compatibilit�, son efficacit�, son degr� de r�versibilit� et ses propri�t�s de vieillissement dans le contexte de son utilisation anticip�e en restauration de peintures. Bien que cet adh�sif est maintenant utilis� dans des domaines tout autres, il n'a pas encore fait l'objet de tests approfondis dans le contexte de ces nouvelles utilisations. Cet article fait le point sur les analyses et les exp�riences d�j� publi�es sur le BEVA 371 et pr�sente une revue de la lit�rature sur l'utilisation de cet adh�sif (en solution ou en film) dans le domaine du traitement des peaux et des cuirs, en mettant l'accent sur sa grande souplesse d'emploi et les facteurs qui influent sur la qualit� de l'adh�-rence. L'article pr�sente aussi une revue historique de l'utilisation du BEVA 371 en solution et en film sur les peaux et les cuirs. L'�tat d'un groupe d'objets en peau qui ont �t� trait�s avec du BEVA 371 au American Museum of Natural History—AMNH (le mus�e am�ricain d'histoire naturelle) au milieu des ann�es 1980 et dans les ann�es 1990 est �valu� afin d'�laborer un suivi des traitements.
TITULO—BEVA 371 y su uso como adhesivo para reparar piel y cuero: antecedentes y revision de tratamientos. RESUMEN—Desde su introducci�n en los a�os 70, el uso de BEVA 371 (soluci�n y pel�cula) se ha extendido desde el campo de la conservaci�n de pinturas hasta el de la conservaci�n de textiles y objetos. Durante el desarrollo de la soluci�n BEVA 371 se condujeron pruebas iniciales para determinar su fuerza, compatibilidad, eficacia, reversibilidad y condiciones de envejecimiento, de acuerdo con su uso, pensado para la conservaci�n de pinturas. Su empleo m�s all� de la conservaci�n de pinturas est� muy difundido; sin embargo, no se han llevado a cabo pruebas completas centradas en esos usos espec�ficos. Este art�culo presenta un resumen de las pruebas y los an�lisis de BEVA 371 que se han publicado y una revisi�n de los tratamientos sobre piel y cuero usando la soluci�n y la pel�cula BEVA 371, concentr�ndose en la versatilidad del adhesivo y en las variables que afectan la fuerza de la adhesi�n. Tambi�n se presenta una visi�n de conjunto de la historia de los usos de la soluci�n y la pel�cula BEVA 371 sobre piel y cuero. Se evalu� el estado de un grupo de objetos de piel que fueron tratados con estos productos BEVA en el American Museum of Natural History—AMNH (Museo americano de historia natural) desde mediados de los a�os 80 hasta fines de los 90.
TITULO—BEVA 371 e seu uso como adesivo em reparos de pele e couro: antecedentes e an�lise de tratamentos. RESUMO—Desde sua introdu��o nos anos 70, a utiliza��o de BEVA 371 (solu��o e filme) tem se expandido da �rea de conserva��o de pinturas para a conserva��o de t�xteis e objetos. Durante o desenvolvimento da solu��o de BEVA 371, foram conduzidos testes para determinar sua for�a, compatibilidade, efic�cia, reversibilidade e durabilidade de acordo com a aplica��o pretendida em conserva��o de pinturas. A utiliza��o de BEVA 371, al�m do tratamento de pinturas, � muito difundida; entretanto, n�o existem testes abrangentes realizados para estes usos espec�ficos. Este artigo apresenta um resumo de an�lises e testes publicados de BEVA 371 e uma revis�o dos tratamentos de pele e couro com solu��o e filme de BEVA 371, enfocando a versatilidade do adesivo e as vari�veis que afetam a for�a de ades�o. Apresenta tamb�m uma vis�o hist�rica do uso de solu��o e filme de BEVA 371 em pele e couro. Avalia a condi��o de um grupo de objetos de pele, que foram tratados entre meados dos anos 80 at� os anos 90 com estes produtos BEVA no American Museum of Natural History—AMNH (Museu Americano de Hist�ria Natural).
In the early 1970s, a new adhesive named BEVA 371 solution was introduced to the field of art conservation. Created by Gustav Berger, the material was originally developed as a consolidant and lining adhesive for paintings and was meant to satisfy several requirements. These included chemical stability, nonaqueous qualities, strong adhesion properties in combination with a variety of substrates, relatively low activation temperatures, minimal pressure necessary during application, ease of removal, minimal effect on original drape of textile substrate, and negligible staining of delicate materials or absorbent paint films.
Following the success of the original BEVA 371 in solution form, other BEVA products were developed, including BEVA 371 film in the late 1970s. The film consists of the original BEVA 371 formula produced as either a 1 or 2.5 mil thick film sand-wiched between silicone release paper and silicone release Mylar/Melinex (Berger and Russell 2000). Although of the same chemical composition, the different physical forms of the solid film and the viscous liquid solution as well as the presence or absence of solvent are important distinctions. These differences allow for a variety of preparation procedures and methods of applications, resulting in different qualities of a lining or repair. During development of the film, Berger (1976) mentioned that such a self-supported film could make it easier to apply and to remove BEVA 371 from fragile textiles and paper without impregnation or staining. Currently, BEVA 371 solution and film are among the most commonly used adhesives in paintings conservation.
For clarification purposes, it should be noted that the original BEVA 371 solution is referred to in the literature not only as “BEVA 371 solution” but also simply as “BEVA” or “BEVA 371” (Berger and Russell 2000). BEVA 371 film is often referred to as “BEVA film” or simply “BEVA.” BEVA D-8 dispersion, BEVA gel, and BEVA gesso are other BEVA products commercially available (Berger and Russell 2000). This article will focus on BEVA 371 solution and BEVA 371 film, and the term “BEVA 371” will be used to refer to both.
Though originally conceived in the context of paintings conservation treatment, over time the use of the two BEVA products was transferred to textile and objects conservation. They are often used as backing adhesives for repairs on skin and leather in North American museums, reflecting original lining applications used in paintings conservation. However, the nature of the materials to which they are applied and the methods of application used are different, which is not surprising, since skin and leather objects are quite different from canvas paintings. They are not usually under tension, they are often three-dimensional, and they are nonwoven. In addition, leather and skins can be highly acidic. Though the normal pH range of vegetable-tanned leather—3.5 to 6.0 (Larsen 1994)—is comparable to the pH of 3.5 to 5.5 of aged canvases (Hackney and Ernst 1994), it can be as low as 2.5 in the case of acid-deteriorated, or red-rotted, vegetable-tanned leather (Larsen 1994). Thus, the BEVA 371 used to back degraded leathers could be in intimate contact with a more acidic environment than when it is used to line deteriorated paintings.
2 REVIEW OF DEVELOPMENT AND ANALYSES OF BEVA 371
2.1 INITIAL INVESTIGATIONS BY GUSTAV BERGER
In 1967, Gustav Berger initiated a research program investigating lining adhesives for paintings. These investigations focused on wax-resin combinations and culminated in the development of BEVA 371 solution (Berger 1984). A series of formulations was developed, composed of a combination of ethylene vinyl acetate (EVA) resins with a variety of waxes and ketone resins. All of these materials were believed to be stable. After subjecting the combinations to accelerated aging environments involving heat-and light-aging, the effects of the various additions and substitutions on adhesive strength and cross-linking were studied, and the best combination was selected—BEVA 371. The original formulation consisted of 500 g Elvax Resin grade 150 and 170 g A-C Copolymer 400 (two ethylene vinyl acetate copolymers of different vinyl acetate contents), 300 g Ketone N Resin (a condensation product of cyclo-hexane), 40 g Cellolyn 21 (a phthalate ester of technical hydroabietyl alcohol), and 100 g oil-free paraffin. The elements were blended to form 38% solids in a solvent mixture of aromatic and nonaromatic solvents (e.g., 1,250 g toluene or xylene and 750 g aliphatic mineral spirits) (Berger 1975). The solid compounds remain the same today (Ketone N is now replaced by Laropal K80, a condensation product of cyclohexanone with the same melting-point range). Only minor variations were made in the composition and proportion of the solvent mixture (Berger 1976) and in the dilution, presently at 40% solids.
As explained by Berger (1976), the key to a hot-melt adhesive such as BEVA 371 is the combination of high and low molecular weight polymers. The high molecular weight elements of BEVA 371 include the ethylene vinyl acetate copolymers: A-C Copolymer 400 and Elvax Resin grade 150. These materials provide structural strength and toughness but have high softening temperatures, 83�C and 116�C respectively. With its softening point at 75–85�C, the lower molecular weight resin Laropal K80 (or originally Ketone N) decreases the mixture's viscosity and softening point. At the activation temperature, it behaves like a solvent that dissolves the EVA polymers and achieves wetting, which is essential in creating a good bond. The plasticizer-tackifier Cellolyn 21 and the wax, each with softening points at 65�C, further reduce the softening point and improve wetting. The wax also affects setting speed and is believed to protect the mixture from irreversible cross-linking, ensuring BEVA 371's future removability (Berger 1976).
During the development of BEVA 371 solution, Berger conducted tests on the adhesive's strength, compatibility, effectiveness, reversibility, and aging qualities in accordance with its intended use in paintings conservation, with positive results. The adhesive's mechanical performance was characterized by testing for peel strength, resistance to shear, and flexural properties. These tests were accomplished on naturally and artificially aged samples (Berger 1972). In testing the aged samples, Berger was able to compare the characteristics of BEVA 371 solution over time with those of other aged samples of conventional adhesives used in painting linings. It is beyond the scope of this article to discuss these analyses in detail; however, it can be generally concluded that BEVA 371 was extensively analyzed and good results were obtained. It was stated that cross-linking of the adhesive would not occur over time and that, if used properly, it could be easily removed from fragile materials without staining or damage (Berger 1970).
2.2 SUBSEQUENT ANALYSES AND TESTING
The following section gives an overview of several studies and assessments of BEVA 371 used as a backing adhesive. Details of the types of assessment and the results obtained are presented in table 1 by date of publication.
As part of the Adhesive Testing Program carried out at the Canadian Conservation Institute (CCI), BEVA 371 solution was analyzed isolated from lining fabrics or supports (Down et al. 1996). This study focused on the properties of the adhesive before and
Results of Select Beva Assessments Organized by Date of Publication
after dark and light aging. Results showed that the pH of the adhesive remained within the acceptable range before and after aging, that minimal volatile emissions occurred over time, and that the adhesive remained flexible upon dark and light aging. Notably, the BEVA 371 solution yellowed significantly upon light aging. Though this may not be an issue aesthetically, yellowing can indicate an instability or degradation of the adhesive (Down et al. 1992). A future CCI research project is to examine the interaction of a range of adhesives over an extended aging period on substrates such as silk, paper, and possibly skin and leather. The purpose would be to investigate whether any deterioration of the substrate occurs due to presence of the adhesive.
Several other studies focused on BEVA 371's bond strength when used as a lining adhesive in painting conservation. These studies investigated how the bond strengths (using peel or lap-shear tests) varied as a function of treatment factors such as application method, temperature, time of exposure to the activation temperature, thickness of the adhesive layer, dilution of the adhesive, solvent used, pressure, type and state of the canvas being lined, lining fabric, and pretreatment of the lining fabric. Katz (1985), Hawker (1987), Pullen (1991), Hardy (1992), Gayer (1992), and Daly Hartin et al. (1993) investigated some of these factors for the BEVA 371 solution. Hawker (1987) accomplished similar investigations for an Adam Chemical Company “BEVA” film of 3.5 mil (this company modified the original formulation of BEVA film and is no longer authorized to produce it), and Forest (1997) focused her research on the BEVA 371 film of 2.5 mil thickness. These studies give useful insight into the wide range of bond strengths that can be achieved with BEVA 371 depending on how it is prepared and applied, as well as on the object and lining fabric it is in contact with. The latter variables will be further discussed in section 3.2. Of the above studies, only Daly Hartin et al. (1993) investigated the effects of natural aging and found no significant trends in change in strength.
Daly Hartin et al. (1993) also found that identically prepared samples of BEVA solution showed a wide range of bond strengths in spite of the high degree of consistency in sample preparation. Thus even small differences in preparation or application, which one may tend to overlook especially in a practical application, can significantly affect bond strength. Interestingly, the film has provided more consistent bond strengths in terms of a lower standard deviation and coefficient of variation as compared to films made with the solution (Forest 1997), a result that the author explains as due to its even thickness and its ease in application with no delays due to solvent evaporation. In other words, the film provides a better control of the range of bond strengths that can be obtained with BEVA 371. Daly Hartin et al. (1993) give a useful discussion on what is considered “adequate bond strength,” pointing out how the concept varies with the lining fabric, the object, and, subjectively, the practitioner.
Benjamin (1994) conducted a practical study focusing on reversal of the adhesive and found that BEVA 371 used for lining may not be as easily reversed as one might hope, the problems being high strength and adhesive transfer to the painting substrate. The author noted that the project was entirely empirical in nature, and she concluded that a more in-depth examination of the process was necessary. Berger refuted her claim that reversibility of BEVA-lined fabrics is not easy, arguing that Benjamin had not closely followed outlined instructions for its use (Berger 1995).
Once the application of the two BEVA 371 products expanded from paintings conservation to the treatment of skins and leathers, related assessments were carried out that focused on practical issues such as ease of use and compatibility. Fenn (1984) describes BEVA 371 solution as an excellent adhesive when used cold and at full strength on native-tanned skin, as well as on oiled and waxed skins. Calnan et al. (1991) noted several advantages of BEVA 371, whether film or solution: it has one of the lowest activation temperatures (65�C) of the conservation choices of thermoplastic adhesives, it does not remain sticky upon cooling, and it produces flexible bonds. BEVA 371 (solution and film) was among the five adhesives that Calnan et al. found most suitable for bonding support fabrics to upholstery leather, and it produced the strongest heat-activated bonds. Alter-natively, the bond created by BEVA 371 used wet at room temperature was too weak to be measurable on a tensometer. Additionally, the authors set up preliminary accelerated-aging experiments focusing on the BEVA 371 solution isolated from a lining fabric, and they found little change in tensile strength or percent elongation after five weeks at 50�C and 0–5% RH.
Though the use of adhesives in textile conservation is infrequent and can have serious drawbacks, they have been employed when textile conservators are confronted with problematic artifacts, such as degraded painted banners or powdery silk flags. If an adhesive is to be utilized, BEVA 371 solution has been found to have certain advantages: it can be applied sparingly to form a nap-bond without impregnating the fibers, and it is quite flexible. There are reports of its use in the 1970s and 1980s in this context, and published observations can give helpful insights to conservators treating skins and leathers. Of particular interest to this review are reports in which treatments using BEVA 371 were revisited years later. Mailand (1998) used BEVA 371 solution to line flags, costumes, and textile upholstery, and one of these treatments, accomplished in 1984 on a 1890s silk costume, was reexamined in 1996. During the later examination, it was found that the areas treated with BEVA were stable in that they had not yellowed or attracted particulate matter, but areas left untreated had continued to deteriorate, showing increased fracturing, probably from movement of the textile. On the other hand, Shore (1994) states that when conservators attempted reversal of BEVA 371 solution–impregnated treatments on cotton and silk, the adhesive had become less soluble, or cross-linked, in as little as five years. Upon rinsing the fabric with solvent, a dark gray discoloration resulted, visible at both the front and back surfaces.
3 REVIEW OF BEVA 371 APPLICATIONS ON SKIN AND LEATHER
3.1 ADHESIVE PROPERTIES SOUGHT
There are several requirements of an adhesive for use in skin and leather repair. Ideally, the adhesive should be compatible with the substrate in its physical and chemical properties. It should not stain or change the appearance of the skin or leather and should remain flexible to allow movement of the object. The bond should be strong enough to hold the repair and to withstand stresses to which the object will be subjected. Such stresses can be induced by the weight of the skin or leather or through the handling required during mounting, exhibition, or travel. In terms of chemical qualities, an adhesive used for backing repairs should not interact with the substrate. It should be chemically stable and have good aging properties, i.e., it should release no harmful vapors and should not weaken over time. Also, the adhesive should be easily removable without adverse effects on the skin or leather. Thus, a stable adhesive that can create a sufficiently strong, flexible nap-bond would be ideal, as this type of bond minimally penetrates the skin and is most easily removed.
BEVA 371 meets most of these requirements. It can create a nap-bond without saturating the substrate. If required, it can be adapted (e.g., used at higher temperatures) in order to flow and more readily impregnate the substrate. It adheres very well to most skins and leathers. As previously mentioned (Fenn 1984), this characteristic is especially true for skin artifacts treated with wax polishes or oily leather dressings to which most adhesives, particularly water-based ones, will not adhere. Concerning aging or stability, BEVA 371 solution has proved to be highly stable according to the testing accomplished at the CCI, and it is assumed that the same holds for BEVA film. Reversibility can be accomplished by exposure to hexane or heptanes for a short time, in either liquid or vapor form, or by mechanical means, with or without heat (Berger 1976).
Compared to BEVA 371 solution, BEVA 371 film is a more recent product, but it is used increasingly for skin and leather repairs. As was seen in section 2.2, the film has been shown to produce more consistent bonds than the solution and gives a higher degree of control (Forest 1997). In relation to these results are BEVA film's practical advantages over BEVA solution: it requires no preparation time, is easier to apply, and is more even and uniform than any film cast in-house. BEVA solution, on the other hand, may need its thickness built up in layers, a process that requires diluting the solution, warming it up, and applying it on a backing either by rolling, squeegeeing, spraying, or flocking. Sufficient drying time is required between each application.
Although BEVA 371 has been used successfully on numerous occasions for skin and leather treatments (see sec. 3.2), in some cases it will fail to meet the objectives of a treatment or simply not succeed as well as an alternative. It can be helpful to examine the reasons invoked in the literature for not selecting BEVA 371 after its initial testing for a skin or leather repair treatment. Dignard (1989, 1992) mentions that BEVA 371 solution was considered for the treatment of tears in a kayak, but was avoided due to the lack of proper solvent extraction. Also, heat-setting or solvent reactivation in this case was difficult because of limited access to the back. Fenn (1984) reports that BEVA 371 solution used at room temperature did not adhere well to gut artifacts such as Inuit parkas and bags made from caribou stomachs. It also altered the translucency of the thin skin (if heat-set, the adhesive is stronger and becomes transparent, but presumably heat was to be avoided for these vulnerable materials). In these instances, more success was found using water-soluble (Klucel G or Modocoll EK1200) or water-dispersed (Elvace 1874 or CM Bond M2) adhesives. Fenn also describes issues concerning the treatment of buckskin shirts with friable pigments rubbed into their surface. Tests suggested that if these were to be treated with BEVA 371 solution, later attempts at reversal with specific solvents could drive the adhesive into the pigments, thus altering the color through saturation. For these reasons, it was believed that the polyvinyl acetate (PVAC) emulsions may give better results. Kite (1991) reports that in the treatment of an alumtawed fur-skin, the film was tested, and, although it held well, it was visually disturbing and seemed to penetrate the skin, making it look translucent. She ended up using a wheat starch paste–sodium alginate mixture with a paper backing material. For the treatment of a sheepskin lining of a saddle, Selm (1989) found that BEVA 371 solution used in solution or cast as a film (and presumably heat-set) gave a weak join, saturated the leather causing staining, and had an unpleasant, lingering smell. Instead, Paraloid B-72 film cast from a 15% solution in acetone was employed. The acrylic film was applied to Reemay and either heat-set or solvent-reactivated with acetone.
3.2 TEAR REPAIRS
Besides its initial use on paintings and textiles, BEVA 371 solution was also used at a fairly early date on leather, specifically upholstery. Sheetz and Cochran (1978) describe backing an upholstery leather piece with BEVA 371 solution and Stabiltex (now called Tetex). They describe the process:“After the [fill] repairs were made, the leather was turned unfinished side up and lined with a reinforcing material, Stabiltex, a sheer synthetic [polyester] material, both flexible and strong. The Stabiltex was placed over the leather and attached to it with BEVA 371, which was melted over the Stabiltex a small area at a time with a warm tacking iron.” Following this publication, literature on BEVA 371 repairs covers a range of objects, such as leather upholstery, saddles, gilt leather, and wall coverings. Most frequently, the treatments involve a system of applying the adhesive to a backing, or carrier, and heat-setting this “band-age” as a repair or stabilization measure. However, there are many interesting variations. The following review attempts to give a different perspective to the published information on skin and leather tear repairs using BEVA 371 by presenting the treatment variables that researchers have quantified (see table 1) and that practitioners have used to achieve the bond they required. It should be recognized, however, that probably the most important variable in determining the strength of the adhesive bond is the object's surface and condition (Berger 1972).
3.2.1 Variables in Manipulating the Adhesive
The quantity of adhesive plays a major role in bond strength. Lining tests have shown that, when heat-setting at 65�C and 70�C, doubling the thickness of the 2.5 mil BEVA film can double or even triple the peel strength (Forest 1997). An increase in weight in the BEVA 371 solution used in a lining context also results in an increase in bond strength when used at temperatures above 60�C (Pullen 1991; Gayer 1992; Hardy 1992). Pullen (1991) also gives correlations between temperatures and thickness of adhesives; for example, a bond strength achieved at 70�C could be produced at 65�C by using 50% more adhesive. None of the treatment articles that were reviewed specified the coat weight when using BEVA 371 solution. For the film, though, not surprisingly, the thickness is usually specified (as given by the manufacturer).
The most common method of applying BEVA 371 solution to the backing material in skin and leather treatments is to spread it on with a brush, allow it to dry, and, if necessary, reapply the BEVA in successive layers. The adhesive can also be spread by using a roller or a squeegee, or it can be sprayed on. As can be expected, the coat weights achieved using these methods can vary greatly (Hardy 1992). Another method of applying the BEVA 371 solution is to flock it onto the carrier fabric. This method differs from spraying in that it produces cobweb-type filaments of adhesive. Flocking is said to help reduce or better control the amount of adhesive applied. This method has been used for the treatment of deteriorated upholstery leather from two 17th-century chairs, using Reemay as the carrier (Howard and Berry 1995). The prepared backing was heat-set in the form of sutures for tears as well as in the form of a full lining to the back of the upholstery. Dignard and Gordon (1999) also use this flocking technique to apply BEVA 371 solution onto Stabiltex (Tetex). The prepared backings were heat-set to individual tears as well as to the full backside of a degraded and powdery fur trim and collar.
Generally in a conservation repair involving a backing, the adhesive is applied to a carrier and not to the object's surface. However, just as the application of a slight sizing of BEVA 371 to the back of a painting has been found to improve adhesion (Berger 1975), some practitioners have applied BEVA 371 to both the skin/leather and the repair material in order to increase the bond strength. Calnan (1992) used BEVA 371 film on the carrier and BEVA 371 solution as a primer to repair tears in Spanish gilt leather. The prepared lining was heat-set in place. Similarly, Sturge (2000) used BEVA 371 solution on the leather as well as the carrier and heat-set the elements in place. Fenn (1984) describes repairs using BEVA 371 solution applied sparingly on the inside of a weakened buckskin artifact. When the adhesive had almost dried, an equally sparing layer of BEVA solution was spread on the lining material and pressed onto the artifact without heat. It is likely that the success of this practice is due in part to an increase in wetting or contact with the object's surface. Experimental tests to compare these various application practices were accomplished by Calnan et al. (1991). They found good bond strengths (as measured by peel tests) resulted when BEVA 371 solution was heat-set after having been applied to the backing fabric alone, to the new upholstery leather alone, and to both the fabric and the leather. A slightly stronger bond was achieved when the adhesive was applied to the leather alone. However, when the tests were repeated using a thinner, deteriorated leather, the most appropriate bond for BEVA 371 was formed by applying the adhesive to the support fabric only, rather than on the leather only (application to both was not tested in this case). These somewhat contradictory results suggest that the condition of the skin object, and perhaps other treatment variables, plays a large role.
BEVA 371 solution has also been tested and used in leather conservation as a discontinuous film applied to a carrier fabric and heat-set onto the object. The optimum arrangement was found to be a series of 2 mm diameter dots, 1 mm thick, 5 mm apart, in a staggered formation. A 1 mm thick aluminum sheet was used to produce the pattern (Calnan et al. 1991). The theory behind this preparation was to provide the backed leather with more freedom of movement when exposed to a fluctuating climate. Tests performed on this repair technique did show an increased flexibility as compared to a continuous film of adhesive, but, as could be expected, a weaker bond resulted. Such a discontinuous film of BEVA 371 solution was used with Reemay to fully support the front-seat cover of a 19th-century Panhard-Levassor automobile (Calnan 1991). This method of application appears to be rare, as there are few reports of its use in the literature.
The activation temperature used will affect the degree of penetration or impregnation of the adhesive into the substrate and the color change or staining of the substrate. BEVA 371 solution becomes tacky at 55�C, liquid with an aggressive tack at 65�C, and at 70�C produces an even stronger bond (Berger and Russell 2000). In the case of the BEVA 371 film, peel strengths on lined canvases were found to vary considerably within this 15�C range of temperature: at 55�C they were too weak to even be measurable using a tensometer; at 60�C they were too low to ensure acceptable lining for a canvas painting (average of 0.05 N/mm); at 65�C they were on average approximately 10 times higher than at 60�C, falling within what was established as an acceptable strength for linings; and at 70�C they were found to be quite strong, being approximately twice as high as at 65�C (Forest 1997). This direct relationship between bond strength and temperature was also measured for BEVA 371 solution (Pullen 1991; Gayer 1992; Hardy 1992). In view of these results, the performance of hot spatulas or other heating devices becomes very important, in terms of the accuracy of the temperature and of its precision (or variability of the heat delivered). Although such data are not outwardly presented in the treatment literature, it is reasonable to assume that treatment temperatures for skins and leathers have fallen within, or close to, this range, depending on the required results. For example, in the treatment of a very fragile, fragmented ermine fur lining of a cape, Kite (1990) mentions heat-setting BEVA 371 film at 70–75�C using nylon gossamer as the backing material. Similarly, Calnan (1991), in the treatment of elements of the previously mentioned 19th-century automobile upholstery, mentions heat-setting a discontinuous film (dots) of BEVA 371 solution at 70�C. Other reported heat-set treatments using the film include the treatment of torn stitchings within a saddle (Sturge 2000), a variety of skin materials including deerskin drums and lizard natural history specimens (Nieuwenhuizen 1998), a pair of fine suede gloves (Kite 1996), and a leather sedan chair (Selm and Bilson 1992). Heat-set examples employing the solution include the repair of Spanish gilt leather (Calnan 1992), repairs to parts of the above-mentioned 19th-century automobile upholstery (Calnan 1991), and the treatments by Howard and Berry (1995), Dignard and Gordon (1999), and Sheetz and Cochran (1978) mentioned earlier. One case study describes the use of very high temperatures to repair fragmented and weakened vegetable-tanned leather car upholstery. During this treatment, BEVA 371 solution was impregnated into the Reemay backing material and heat-set to the leather at 100�C using a short contact time (Sturge 2000). This is said to have allowed some reshaping of the leather while the BEVA was warm and soft, while producing a strong, secure bond once the adhesive was cool. In the vast majority of cases, such high temperatures are avoided for degraded skins and leathers.
BEVA 371 bonds quasi-instantaneously once the activation temperature is reached (over 60�C), but if the activation temperature is applied for a length of time, the bond strength is significantly affected. In a series of lining tests, Forest (1997) found that, with the hot table used, it took approximately 12, 14, and 18 minutes to reach the activation temperatures of 60, 65, and 70�C respectively, and about 20 minutes to cool back down to room temperature. If a holding time of 10 minutes was added when each activation temperature was reached, a bond of twice the peel strength resulted, as compared to the bond created with no holding time. In particular, it was found that at 65�C with no holding time, the bond was too weak for half of the samples. But, with the 10-minute holding time under the same conditions, the peel strengths ranged between moderate and too strong. Also, it is likely that the rate at which the BEVA 371 is heated and cooled may affect strength (Forest 1997). Holding time was not found to be reported in the treatments surveyed, but it would be expected to be in the range of seconds or tens of seconds rather than minutes. Rate is never mentioned either and most likely varies with the type, quality, and age of the equipment used.
Another treatment variable that affects bond strength but is not often quantified in skin and leather treatments includes the amount of pressure applied (Gayer 1992). In the case of the BEVA 371 solution, the amount of solvent retained or the length of time for solvent evaporation to occur prior to use will also have an impact on bond strength (Hardy 1992).
Conservators have often chosen to use BEVA 371 solution without any heat beyond room temperature to avoid potential heat damage. This technique results in a weaker bond than that achieved through heat-setting (Calnan et al. 1991). In some cases a weak bond is all that is required. Boulton (1986) describes repairs to a pair of Aleutian Islands boots using BEVA 371 solution diluted in toluene, brushed onto goldbeater's skin, and applied at room temperature. Fenn (1984) also mentions the use of BEVA 371 solution without heat with various nonsynthetic backing materials to repair Inuit clothing water-proofed with sea mammal oils and also native-tanned clothing. Kronthal (2001) experimented with BEVA 371 solution at room temperature for some repairs to rawhide shadow figures.
In painting conservation, if temperatures lower than the activation temperature are required, they can be obtained by spraying films of the BEVA 371 with solvents. According to the BEVA 371 film technical data sheet, spraying the film lightly with naphtha makes it tacky at about 38–43�C (methylene chloride is also mentioned, but it is highly toxic). For BEVA 371 solution, the activation temperature can be lowered to 40–45�C or less by lightly spraying with aromatic mineral spirits. It can also be lowered by using the adhesive about two hours after applying it to the backing material, while it still retains some of the solvents (Berger 1975). No references to using BEVA 371 in this way on skins and leathers were found in the literature.
Another method of using BEVA 371 that avoids the use of heat is solvent reactivation of the dry film. The solvent can be sprayed onto the film or, for small repairs, applied with a syringe or a fine brush. If the solvent is applied with a syringe, it becomes possible to position the adhesive-covered carrier behind the object while the adhesive is in a dry state, an advantage shared with the heat-setting technique. The amount of time that good contact must be held through the application of pressure before the bond is achieved can be short, but it depends on the type and quantity of solvent used. In comparison, heat-setting involves quasi-instantaneous bonding time. Solvent reactivation was one of several methods used by Kronthal (2001) in the treatment of shadow puppets. In this context, goldbeater's skin was brushed with the BEVA 371 solution. This solution was left to dry as a film, and the backing and adhesive were applied by reactivation with naphtha or petroleum benzine. Though this technique was sufficient in many cases, a stronger bond was achieved with other adhesives in combination with the gold-beater's skin.
3.2.2 Choice of Lining Material
Many carrier materials have been used for skin and leather repairs, depending on the nature of the substrate and the required results. Their composition, method of construction (woven or nonwoven), and nap can affect the bond strength (Calnan et al. 1991; Gayer 1992; Daly Hartin et al. 1993; Forest 1997; Berger and Russell 2000) as well as flexibility of the repair.
Both spun and woven synthetics have been used successfully, including Stabiltex (Tetex) woven polyester (Sheetz and Cochran 1978; Dignard and Gordon 1999), Hollytex spun polyester (Nieuwenhuizen 1998), Reemay spun polyester (Kaminitz and Levinson 1988; Calnan 1991; Howard and Berry 1995; Nieuwenhuizen 1998; Sturge 2000), Dacron woven polyester taffeta (Tsu et al. 1999), Arvex woven polyester or polyester sailcloth (Calnan 1991; Calnan 1992; Selm and Bilson 1992), and Cerex or nylon gossamer (Kaminitz and Levinson 1988; Kite 1990; Calnan 1991; Selm and Bilson 1992; Kite 1996).
Natural materials have also been used. Tsu et al. (1999) describe repairs to tears within an 18th-century gilt wall hanging using Japanese paper with BEVA 371 solution in combination with the BEVA gel. Fenn (1984) used both new oil-tanned skin and cotton fabric with the BEVA solution in treating native tanned skins (Fenn 1984; Tsu et al. 1999). Skin lining materials, such as goldbeater's skin and natural skin condoms, have also found useful applications. For example, Kronthal (2001) found that the translucent properties of goldbeater's skin matched those of a collection of Chinese shadow puppets while also producing a strong, flexible mend. Boulton (1986) has also used goldbeater's skin with BEVA solution at room temperature to treat Aleutian boots.
One can utilize BEVA 371's thermoplastic properties and flexibility to create a fill material and to replicate textured surfaces. Calnan et al. (1991) investigated a series of possible polymeric fills, including the use of BEVA 371 film. They found that the heated film could be worked to create a flexible and extensible fill and had the following advantages: it requires virtually no drying time, it is easy to reverse with heat or solvents, and it is easily overpainted with acrylic emulsion paints. They also noted that the fill material needed reworking to ensure a smooth finish and uniform adhesion and had a tendency to spill over onto the immediate surrounding leather surface. In this case, the preferred application involved heat activation of small rolls of the film placed in the crevice and building up the fill material in layers to ensure that the adhesive was fully activated and bonded well to the leather. Kaminitz and Levinson (1988) used the solvent form of BEVA 371 mixed with dry pigments and glass microballoons to fill losses in untanned skin stretched over wooden drums and harps. The mixture was applied in a thin layer over an insert of Japanese tissue paper or synthetic web fabric. In this case, considerable strength was required to join the fill material to the very thin edges of the loss, and great flexibility was necessary to allow the skin to respond to environmental changes without separating from the fill. Nieuwenhuizen (1998) mixed warmed BEVA 371 film with dry pigments and glass microballoons and applied it as a fill material to replicate textured surfaces. In this case, the solution was avoided in an attempt to minimize shrinking. Sturge (2000) describes the use of colored BEVA “sticks,” made by mixing small amounts of dry pigment into BEVA 371 solution and allowing the solvents to evaporate after spreading the mixture onto silicone paper. Once dry, the solid BEVA 371 can be cut into strips and melted into cracks and splits using a heated spatula.
4 ASSESSMENTS OF PAST AMNH TREATMENTS OF SKIN
4.1 ADHESIVES USED AND RATIONALE
BEVA 371 was introduced as an adhesive in the objects conservation laboratory at the American Museum of Natural History (AMNH) in 1985. Initially it was utilized in its solution-based form, either applied directly to the edge of the join if it was very small, such as in a butt join of a fringe element, or applied to a lining material and, upon drying, heat-set or solvent-reactivated in place. After BEVA film became available, it soon replaced the solution as the predominant BEVA 371 adhesive form used. A small selection of lining materials has been used with BEVA at the AMNH, primarily Reemay, Cerex, and goldbeater's skin.
Three other types of adhesives were used less frequently on skins during this period. These included polyvinyl acetate (PVAC) resins, Lascaux 498 HV acrylic dispersion, and Paraloid F-10 acrylic resin. Though the PVAC resins (grades AYAA and AYAC) were often favored among these because of their working properties, BEVA 371 heat-set continued to predominate over all choices. It was found that there was increased control over the degree of saturation of BEVA 371 into the substrate and therefore fewer tendencies for the adhesive to stain.
The focus of the evaluation to be described in the next section was to assess the long-term stability of repairs made using BEVA 371. These assessments were made by visual and physical examination of the repairs and the surrounding areas of skin. Some interesting trends were noted during the survey in relation to the other adhesives mentioned above, and these observations will be summarized as well.
4.2 ASSESSMENT OF BEVA-BASED TEAR REPAIRS
In 2002, 58 ethnographic skin objects treated during the years 1985 to 2000 using either BEVA 371 or other selected adhesives were reexamined in an attempt to determine the long-term stability of the repairs. The objects surveyed included skin clothing and apparel such as coats, leggings, aprons, bags, and shoes and musical instruments such as drums and harps. The types of skins examined included untanned (rawhide) and tanned (brain, oil and smoked) skins. A total of 49 of the 58 objects in the survey had tear repairs or fills made the BEVA 371 products.
The results of the survey demonstrated that an overwhelming majority of repairs and fills utilizing BEVA 371 were still intact and flexible from 2 to 17 years after treatment. A small number of these objects (5 out of a total of 49, or 10.2%) had repairs that had either failed or were beginning to exhibit minor changes, such as lifting or incipient lifting of the lining material from the substrate. It should be noted that the number of repair sites on an object varied from one to more than a dozen, and if just one backing out of several was beginning to separate, this treatment was counted as exhibiting changes. Of the five objects that exhibited changes indicating failure, three consisted of tear repairs made using BEVA film and two consisted of fills whose media was BEVA solution. No other types of deterioration, such as stiffening or related discoloration of the skin or adhesive, were observed. It is also important to note that all five of the objects exhibiting some degree of repair failure were included in traveling exhibits. As such, these objects were subjected to extensive handling engendered by repeated packing, unpacking, and placement of the objects on mounts.
Of the small number of objects with failed tear repairs (3 out of 40), the cause of the deterioration of each repair can be explained by choices made by the conservators, rather than by aging or deterioration of the adhesive. As previously outlined, many variables can affect bond strength, such as the choice of backing material, the quantity of adhesive applied, the temperature used, and the dwell time. A more precise cause of failure is sometimes difficult to pinpoint. Factors that appeared to promote weak or failed repairs in these cases included poor choice or preparation of the lining materials, inadequate size of lining material, and possibly inadequate preparation of skin surface prior to repair application.
Most commonly, the lining material may not have been properly matched with the weight and flexibility of the object, or the adhesive was insufficiently or inadequately applied to the backing. A thick-grade Reemay was often intuitively chosen as the lining material for large or heavy objects or for repairs on thick, relatively inflexible skins because of its heavier weight and strength. Such a choice was made, for instance, for the repair of a Mangbetu fur belt with numerous heavy dangling ornaments. The linings were applied with BEVA 371 film to stabilize the incipient tears on this object. Examination of the belt revealed that two of the five backings were in the process of completely separating from the surface, and another two linings exhibited lifting around their edges. These results may be partially due to incomplete application of the adhesive all the way to the edges of the backing as well as the use of cut rather than feathered edges. In retrospect, Reemay may sometimes be too thick or tough a lining material for particular objects. It is difficult to feather out and it loses adhesive during the feathering process, therefore providing less contour and grip at its edges. This loss becomes especially problematic for objects that are flexed during handling. Feathering the edges plus using an excess of adhesive at the edges would probably ameliorate much of the edge lifting seen within repairs using Reemay. Furthermore, observation of numerous repairs during the course of this survey indicated that for thick skin objects, such as the Mangbetu belt, application of two layers of Cerex, a thinner backing material, sandwiched with a second layer of BEVA film may provide better longevity.
A complicating factor when analyzing the cause of repair failure as seen on the Mangbetu belt is the fact that the belt was oil-tanned during manufacture and may have retained oily residues on its surface. While BEVA 371 has been recommended as an adhesive for oily or waxy surfaces, it is possible that the residues left on the skin surface of the belt may have compromised the integrity of the mends. Repairs of this type would probably be more successful if the skin were superficially degreased by swabbing with an appropriate solvent for oils prior to application of the BEVA and backing. Additionally, past treatments on objects at AMNH also exhibiting oily surfaces, such as Chinese shadow puppets, indicate that stronger bonds may be obtained through direct application of BEVA 371 solution to the surface of the repair area and, upon drying, heat-setting BEVA film with the appropriate lining.
Examination of numerous repairs and fills applied to a highly deteriorated shaman's apron from the Luba culture of Africa revealed a Cerex backing lifting from the skin surface at one repair site, with a strip of inadequately heated BEVA film remaining as a separate intact layer. Treatment procedures outlined previously such as temperature and exposure time to heat are important factors in these kinds of repairs. As with the choice and preparation of lining materials, conservators should be meticulous about ensuring that a complete bond is achieved during execution of the treatment. Additionally, this object had a number of cut rather than feathered backings that were lifting at their edges. Upon examination of the reverse side of the backings, it was evident that the BEVA film had not been applied all the way to their edges. Even if the edges of a backing are a significant distance from the area requiring support, an inadequately adhered lining edge could lead to further lifting of the lining if the object were to undergo excessive handling.
Another example of repair failure occurred as a result of handling during the course of this survey. A Blackfoot shirt was fit quite snugly on a mannequin. Manipulation to examine a Reemay–BEVA film repair caused the backing to completely detach from one side of the join. It was not clear what the source of this join failure was. While the surface area of the join was adequate, the appearance of the adhesive on the detached backing seemed to indicate that the repair may not have been carried out to a sufficient degree of saturation (as controlled by the dwell time) or with enough heat. Both of these treatment elements would be necessary to ensure a sufficiently strong bond to withstand the handling and continual stress of years on a closely fitted mannequin.
A final source of join failure was observed on another of the artifacts surveyed. In this case a detached tassel of a Blackfoot bag that was repaired prior to travel in a multistop exhibit clearly failed, as neither the tassel nor the lining was extant at the time of the survey. For this repair, the lining material used for the join was probably too small for the requirements or the use of the object. Other remaining tear repairs at less vulnerable locations on the object were extant but were very tiny in size. It should be noted that the lining material must span a sufficiently large area beyond the tear to provide ample surface for the adhesive mend, thus allowing for handling and manipulation of the object.
Most of the failed repairs described above were executed 12 to 17 years ago. It is clear that a history of the use of BEVA over this period of time engendered experimentation with techniques that led to greater finesse in skill. As mentioned, none of the BEVA 371 tear treatments appeared to fail as a result of chemical problems within the adhesive, but instead from specifics concerning inappropriate treatment decisions and procedures chosen for the particular object.
4.3 ASSESSMENT OF BEVA 371–BASED FILLS
Nine of the 58 objects in the survey had applied to them fills that used BEVA 371 solution as the adhesive element. The composition of the fills made to skin or leather objects utilizing BEVA 371 was of two types: those that included glass microballoons as the inert filler and those that included cellulose powder or pulp as the inert filler. Both types of fills were internally colored by the inclusion of dry pigments in their mixtures. These fill mixtures were empirical. They were not formulated according to weighed-out amounts; hence, their properties could vary widely. Too much inclusion of the inert fillers could result in less flexible fills or fills that could separate from the edges of the skin due to inadequate tack or adhesion.
Earlier fills at AMNH consisted of mixtures of BEVA 371 solution mixed with glass microballoons and dry pigments applied over Reemay backings (Kaminitz and Levinson 1988). These fills were often used to replace losses or cracks in rawhide coverings that were stretched over the wooden bodies of musical instruments. Where possible, Reemay or another type of backing was slipped under the skin and held in place using PVAC resin (chosen for its high degree of tack). At times narrow surface cracks in the skin were filled with the mixture in order to achieve visual integration; this was necessarily accomplished without the backing. More often, the BEVA mixture, of thick putty consistency, was applied over the Reemay with a spatula, and upon setting was shaped and textured with a heated spatula. Because there is a high degree of tension in the stretched leather or skin, these instruments are particularly reactive to fluctuations in temperature and relative humidity. Therefore, the fills required sufficient flexibility to allow for movement of the skin over the rigid core and adequate cohesive strength and tack to adhere to the thin edges of the remaining skin.
Of the nine objects with fills that were examined, six were musical instruments treated with BEVA solution–glass microballoon fills. The instruments were on exhibit for 2 years, traveled to several venues, and then spent 10 years in a stable storage environment. During travel, one of the objects with narrow, unbacked fills exhibited separation of the fill from the surrounding skin. It was easily remodeled with a heated spatula to the edges of the skin. During the recent survey, this harp again exhibited slight separation of the same fill from the edges of the skin. Another harp that initially showed severe distortion of the skin and numerous repairs was stable during the length of the exhibit. However, with time the skin has contracted, causing the fill to separate to an unacceptable degree. Thus, the survey revealed that two out of six repairs to objects of this type exhibited some degree of instability. The release of the edges of the fill from the skin appears to be a failure of a physical nature and is not attributed to the chemical stability of the resin. Given that there is so little of the actual adhesive present along the edges of these fills, and given the inordinate amount of strain and flexing that such a repair can undergo, this degree of failure is not surprising. This is especially the case with the fluctuations in temperature and relative humidity posed by travel. Perhaps pretreating the edges of the loss with BEVA 371 solution and then applying the fill material would prevent such failure.
In another early repair, the BEVA 371–glass microballoon fill material was applied directly to the surface of a couple of tassels on the vegetable-tanned skin of an African club, thinly filling surface losses that had resulted from insect grazing. The tassels, though fragile because of such extreme loss, were not backed to lend more strength. Currently, they are intact, though the fills are separating around their edges from the skin. Again, the instability of these fills appears to have nothing to do with a chemical interaction of the adhesive and skin. Instead, it appears to be an example of inadequate choice of repair technique by the conservator in which a simple backing would have better addressed the issue of stability. No matter how much flexibility or tack the adhesive may have, application of a small fill to a very mobile, flexible element will most likely result in separation of fill edges from the substrate.
The second type of fill mixture, consisting of BEVA 371 in solution with cellulose powder or pulp and dry pigments, was developed to be a more flexible fill material. It was used in the laboratory from 1997 to the present, specifically to fill losses in two objects composed of deteriorated skins with sueded surfaces—a Luba shaman's apron and a Yakut shaman's coat. The mixture was used over Reemay or Cerex backings and, in these cases, was applied to objects that required a considerable amount of handling prior to exhibition. The two objects thus treated have remained remarkably stable. The fills currently retain their flexibility, and the adhesion of the fills to the edges of the skin has been sufficient throughout the handling imposed during mount making, packing, and exhibit. It should be noted that the flexibility of this fill material can vary from fill to fill because of the empirical nature of the mixtures. This inconsistency could be easily addressed by using weighed-out formulations to create facsimiles, obtaining more reproducible properties.
4.4 ASSESSMENT OF AYAA AND AYAC (PVAC) RESINS AND LASCAUX 498 HV REPAIRS
Of the 58 objects reexamined in the survey, 10 included repairs made using PVAC resins (AYAA or AYAC) or the acrylic dispersion Lascaux 498 HV consisting of 56% butylacrylate-methylmethacrylate copolymer (Down et al. 1996). Though considerable treatment failure was noted in this group, no conclusions have been made about the reasons for the failure since the sample size is too small and it is outside the scope of this study. However, interesting trends were noticed. Of the seven objects that were repaired using one of the PVAC resins, two had mends that had failed. Visual inspection indicated that the reasons for these failures could be similar to some of the failures seen with BEVA 371 repairs. In one case, the backing size was possibly inadequate for the repair demands of a highly responsive drum skin; in the other, the repair was made using discrete dots rather than a continuous bead, which has been shown to be a weaker repair method. None of the adhesives at these failed joins appeared particularly degraded or yellowed.
Two objects repaired using Lascaux 498 HV were also reexamined, and both exhibited some degree of failure. In one case, the adhesive was chosen because the conservator wanted a weak bond that would release if the area of the mend was under too much pressure. In that sense the treatment could be considered successful, as the repair backing had totally released from the drum skin. In another situation, the synthetic web backing material employed appeared too thin for the weight and flexibility of the object— a large, extremely heavy tipi. Additionally, the adhesive may not have had enough strength for the necessary repairs. The high percentage of failure in this small sample size suggests that further examination and study may be needed.
4.5 SUMMARY OF ASSESSMENT RESULTS
A survey was conducted of nearly 60 skin and leather artifacts at AMNH treated between 1985 and 2000, where the majority of repairs used BEVA 371 film or solution as the adhesive. Results indicated that in most cases the BEVA 371 tear repairs and fills have remained intact: they are visually unchanged, and the mends continue to provide the stability required. Of the 10% that showed any degree of failure, the changes could usually be explained by unsuitable treatment decisions often closely related to how the object would be used in the future. Several factors that could influence the long-term success of these repairs include the nature, size, and thickness of the backing material, the degree of heat used and the time it was applied, and the degree of saturation of the adhesive into the skin and the backing. As expected from its known stability, chemical deterioration of the adhesive does not appear to be at cause. In the few instances where the adhesive failed, or was intentionally reversed to provide a view of the adhesive under the backing material, no yellowing or other discoloration of the adhesive was observed. It is clear that individual treatment procedures and choices are key factors in the longevity of repairs made with this substance.
5 FUTURE ANALYSES
BEVA 371 solution and film have been adopted by objects and ethnographic conservators as adhesive options for treatment repairs, in part because of their known stability. It would be useful to have more information on their long-term aging properties when in contact with skin and leather, specifically the effect the adhesive has on the physical properties of these materials. Additionally, though it has been used successfully for many years on other acidic substrates such as aged canvases, more testing and analysis of its properties when in contact with the acidic environments provided by skin and leather are critical. Conservators at the AMNH and scientists at CCI have begun discussions concerning future efforts to further understanding of the long-term properties of BEVA 371 film when used for skin and leather repair. Three goals have been developed: to determine how BEVA 371 ages in the acidic context of vegetable-tanned leather; to determine the effects the aged adhesive has on the skin; and to determine if, upon aging, there are changes to the bond between the adhesive and the skin. Most of the experiments will closely follow methodologies laid out by CCI in its ongoing adhesive studies of PVAC and acrylic resins and will complement analysis to be accomplished from sampling from the AMNH collections. The AMNH project will involve removing both adhesive and skin samples from artifacts treated with BEVA 371. Shrinkage temperature measurements will be accomplished on collagen samples taken from untreated areas of artifacts and will be compared with those taken from reversed repairs, where the adhesive was in contact with the fibers. It is believed that this could help determine if the adhesive had a deteriorating effect on the skin.
The literature on adhesive repair treatments using BEVA 371 was reviewed to provide an overview of the broad range of applications that the adhesive has had with skin and leather objects over the years and the many variables that can affect the outcome of the treatment. Understanding the physical and chemical properties of BEVA 371 solution and film has allowed conservators the ability to manipulate the adhesive and its application methods to accomplish the needs required by a wide range of materials. Comparing results of the literature survey to actual assessments on collections has provided insights into how the repairs actually respond over time to these variables as well as to external forces. In the rare cases where failures were observed, it was concluded that these were due to poor treatment decisions and an underestimation of the bond strength required to withstand handling, not to chemical deterioration of the adhesive. A CCI-AMNH collaborative project is planned to further investigate the properties of BEVA 371 film used in contact with acidic skins and leathers.
The authors would like to thank those conservators and conservation scientists who have published their experiences and research concerning the use and properties of BEVA 371 in paintings, textiles, and objects conservation. Making these results available has allowed for a more comprehensive understanding of this material.
In addition, the following colleagues who reviewed this article and provided useful comment are gratefully acknowledged: Debra Daly Hartin of the Canadian Conservation Institute, Elisabeth Forest of the Centre de conservation du Qu�bec, and Monika Harter of the Adelhauser Museum in Freiburg, Germany. Most especially, we extend our appreciation to Gustav Berger for the development, introduction, and analysis of an adhesive very useful to the field.
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Rohm and Haas Co. Independence Mall West Philadelphia, Pa. 19126BEVA 371 film (1 mil and 2.5 mil)
Conservator's Products Company P.O. Box 411 Chatham, N.J. 07928BEVA 371 solution
Conservator's Products Company P.O. Box 411 Chatham, N.J. 07928Cellulose powder
Whatman cellulose powder for partition chromatography Fisher Scientific 4500 Turnberry Dr. Hanover Park, Il. 60103 (630) 259-1200 (800) 772-6733 www.fishersci.comCerex—nylon gossamer
Talas 568 Broadway New York, N.Y. 10012 (212) 219–0770 www.talasonline.comGlass microballoons, 3M Scotchlite glass bubbles, goldbeater's skin
Talas 568 Broadway New York, N.Y. 10012 (212) 219–0770 www.talasonline.com
Talas 568 Broadway New York, N.Y. 10012 (212) 219–0770 www.talasonline.comLascaux 498HV
Talas 568 Broadway New York, N.Y. 10012 (212) 219–0770 www.talasonline.comPaper pulp, 289 pulp, ash-free analytical filter paper
Schleicher and Schuell Keene, N.H. 03431Reemay—spun polyester
Talas 568 Broadway New York, N.Y. 10012 (212) 219–0770 www.talasonline.com
LISA KRONTHAL received a B.A. in art history from the University of Rochester in 1988 and an M.A and certificate of advanced study in art conservation from the State University College at Buffalo in 1993. She began working at the American Museum of Natural History in 1994 as a conservator in the Anthropology Division specializing in archae-ological and ethnographic objects and is currently the conservator of Natural Sciences Collections working out of the Office of the Associate Dean of Science for Collections. She is a professional associate of AIC and currently cochairs the conservation committee within the Society for the Preservation of Natural History Collections (SPNHC). Address: American Museum of Natural History, 79th Street at Central Park West, New York, N.Y. 10024.
JUDITH LEVINSON received a B.A. with honors in anthropology from the University of Pennsylvania (1973), a master's of fine arts (1977) from the Cran-brook Academy of Art, an M.A. in art history and a certificate in conservation from New York University, as well as a certificate in objects conservation from Harvard University, Fogg Art Museum. She has worked as head conservator in the Anthropology Department at the American Museum of Natural History since 1985 and has been an adjunct professor of conservation at the Conservation Center, New York University, since 1989. Address: Anthropology Department, American Museum of Natural History, 79th Street at Central Park West, New York, N.Y. 10024.
CAROLE DIGNARD has a B.Sc. in physics and Italian (1981) and an honors B.A in classical studies (1983) from the University of Ottawa, and a master's degree in art conservation (1986) from Queen's University. She has been working in the objects section of the Canadian Conservation Institute since 1988. She is a professional associate of AIC (1993) and an accredited member of the Canadian Association of Professional Conservators (1994). She was one of the instructors of the Canadian Conservation Institute's workshop “Adhesives for Textiles and Leather Conservation: Research and Application,” which was delivered four times between 1999 and 2001. Address: Canadian Conservation Institute, 1030 Innes Road, Ottawa, Ontario, Canada K1A 0M5
ESTHER CHAO graduated summa cum laude from the University of Arizona with a B.A. in anthropology and a B.A. in art history in 1996. She received an M.A. in art history and a certificate in art conservation from the Conservation Center, Institute of Fine Arts, New York University, in 2001, specializing in objects conservation. She completed her fourth-year internship at the American Museum of Natural History and is an Andrew W. Mellon Fellow at the Smithsonian Institution's National Museum of the American Indian. She is currently working in the conservation laboratory at the Peabody Museum, Harvard University. Address: Peabody Museum, Harvard University, Conservation Department, 11 Divinity Ave., Cambridge, Mass. 02138
JANE L. DOWN graduated from Queen's University, Kingston, Ontario, with an honors B.Sc. in chemistry and mathematics in 1973. In 1978, she joined the Canadian Conservation Institute (CCI) and is the senior conservation scientist who is responsible for all adhesive research done at the institute as well as answering the numerous adhesive-related inquiries that CCI receives worldwide each year. She has published many papers and articles on adhesives, presented her work at various national and international conferences, and organized and taught several adhesive workshops, including CCI's “Adhesives for Textile and Leather Conservation: Research and Application.” She is an accredited member of the Canadian Association of Professional Conservators and a Fellow of the International Institute for Conservation of Historic and Artistic Works. Address as for Dignard.