Volume 18, Number 3 .... September 1996

Technical Exchange

Inpainting with Kremer's Wood Stain / Varnish

Matching deep black colors is probably one of the more difficult aspects of inpainting. A common solution among many conservators is to use combinations of Ivory or Spinel Black with Alizarin Crimson, Prussian Blue, Permanent Green Deep, Blue Violet, and Indian Yellow, to create deep vibrant black hues. These pigments usually work quite well, however in some cases, especially on smooth panel paintings, inpainting can build up producing matte granular textures.

Woodstain varnishes are pure metal-complex-powdered dye-stains that (according to the Kremer catalog) are the successors of aniline dyes. They are extremely potent, soluble in ethanol, and have very high coloring strength. Woodstain powders disperse beautifully in PVA (Mowilith 20 in ethanol). Unfortunately, they are only slightly soluble in xylene. It is possible, though, to take a little ethanol or acetone into your brush and pre-dissolve them on your palette before working into a varnish resin diluted with a hydrocarbon solvent.

The accompanying safety data sheets (provided by Kremer) list the following chemical characterizations for the Woodstain colors: Blue, Phthalocyanine metal complex, CI Solvent Blue 70; Woodstain Red, azo dye / chrome complex; Woodstain Yellow, metal complex dye - C.I. Solvent Yellow; Woodstain Blue, metal complex dye / contains Cr (III) - Solvent Black 27. Kremer describes these materials to have good lightfastness . Even though these dyes are considered to be much safer than aniline dyes, extra precaution should still be taken not to inhale or get the substance on your clothes or skin.

One concern of mine is that these dyes may have the potential to stain porous paint film during future cleaning. This is certainly a possibility if concentrated amounts are used without an isolating varnish. In my experience, the most important feature of these dyes is the ability to make slight translucent adjustments in very deep colors while maintaining a very glossy (saturated) surface.

Dean Yoder

Regalrez Low Molecular Weight Varnish: Matting Agents

Gamblin Artists Colors Co. manufactures a kit varnish made of Regalrez resin, Kraton rubber, Tinuvin 292, and solvents. We have been involved in a couple of projects where it has been necessary to reduce the gloss of the varnish to obtain a specific "look" that the artist preferred. Tests using fumed silica and unbleached white beeswax as matting agents, revealed two interesting findings: 1) 5% of wax was required to equal the matting properties of .5% fumed silica; 2) All percentages of fumed silica left the varnish transparent, but even the smallest percentage of wax made the varnish solution cloudy. In order for fumed silica to be used as a matting agent one must have the right equipment to fully disperse it into the varnish system. A high speed disperser is needed, laboratory models work well for even small amounts.

Robert Gamblin

Grounds for Paintings

The ASTM Committee on Artists Materials (Committee chair, Mark Gottsegan; Physical Properties Subcommittee Chair, Robert Gamblin) has started the process to write a quality standard for acrylic grounds. We want to initiate a study of the relative merits of acrylic grounds, traditional glue/oil grounds, and alkyd grounds. Also to be investigated are substitutes for hide glue as sizes for canvas.

At this time we are soliciting information from artists and conservators about their working habits in preparing grounds and about incidents of failure of adhesion of paint layers to grounds that you may think are interesting to our committee.

Please send responses to:

Conservation of a Feast of Sugars

The Day of the Dead, or Todos Santos, is the most important festival of the year in Mexico and celebrates the return of the souls of the dead to earth. This was the subject of an exhibition at the Museum of Mankind, London, England, entitled "Skeleton at the Feast" which opened in 1991 and closed in October 1992. The extraordinary and colorful exhibition reflected the vibrant and lively nature of the festivities through displays that include flowers, candles, pottery vessels, papier mache figures, toys, and also several hundred sugar sculptures, which are the subject of this short article. Examples of such material have entered the British Museum collections since the 1960's, with comparable pieces in other collections, dating back to the late 19th century. The more recent acquisitions are in good condition, but the potential for deterioration can be seen from the condition of the earlier material, which has significantly discolored and become more friable.

The sugar objects represent a variety of forms ranging from skulls, sheep, deer, coffins, skeletons, and birds, to flowers. They are made from a basic mixture of icing sugar, egg whites, and sometimes lemon juice to whiten the mixture. They are cast in molds and additional features and decorations are applied afterwards, sometimes incorporating colorings.

The exact nature of sugar deterioration is not fully understood and is made more difficult to investigate by the variable composition of the sugar artifacts. The sugar used in the creation of the objects is sucrose (domestic sugar) with varying additions and quantities of the above ingredients. Discoloration (i.e., browning) of sucrose is a commonly observed consequence of deterioration. Basically, the sucrose deteriorates in the presence of moisture and heat by converting into reducing sugars such as glucose and fructose, which in turn react with proteins (e.g. egg whites) causing browning.*

The condition of the material was generally quite good, insofar as there were no detectable signs of browning in the majority of the recently acquired collection. However, many of the fragile pieces had been broken in transit. Thus, remedial work was required and extreme care was necessary when handling the objects. Other problems included objects covered with a powdery sugar decoration that was vulnerable to loss. Another group of objects were glazed with a sugary solution which remained tacky and liable to attract dust and adhere to adjacent materials such as storage materials and packing supplies. No treatment was possible for this problem. Wearing gloves was important in handling these objects because moisture and heat from bare hands literally cause a "sticky situation."

All conservation work was carried out in a purpose-built storeroom with an air-conditioning unit to maintain an environment of low relative humidity (below 30%) and low temperature (10-15°C or 50-59°F); these conditions are believed to minimize the rate of discoloration.*

Joining broken fragments and consolidation were the major treatment requirements. A variety of adhesives were considered - the criteria being good aging properties, suitable strength, low polarity solvent, good working properties at low RH, and reversibility. The combination of materials finally selected for use were: 1% Klucel G (hydroxy-propyl cellulose) in IMS to consolidate broken edges and friable surfaces, and 30% Paraloid B72 (ethyl methacrylate copolymer) in isopropanol as the adhesive. These were found to be the most satisfactory in fulfilling all the above criteria.

Glass microballoons in 3% Paraloid B72 in isopropanol, which closely matched the appearance of the white sugar, were used to fill in missing areas. The complex and often imbalanced forms of the sculptures often made support during setting of the adhesive difficult.

The sugar sculptures were scheduled to remain on exhibition for two years (until 1993) in cases which achieved and maintained a low relative humidity and temperature by means of an air conditioning unit. At the time of this article, the conservation procedures appeared to have been successful and there was no apparent change or discoloration in any of the sugar objects on exhibit.

*Daniels, D., Discoloration of Sugar Artifacts - Interim Report, British Mus. Dept. of Con., Conservation Research Internal Report, v. 18 (1988).

I would like to thank Dean Sully and David John Lee of the Organic Artifacts Section, Dept. of Con., British Mus., for their considerable help and assistance with this work, and Vincent Daniels of the Con. Res. Group, for his research on the discoloration of sugar.

This article was reprinted with permission from the ICOM Ethnographic Conservation Newsletter, No. 13, March 1996.