Volume 17, Number 1, Jan 1995, p.10

Technical Exchange

Replacement for Triton X-100

If you have read the Health and Safety column in this issue, you know I have concerns about the safety of Triton X-100. A few months ago, I mentioned these worries to Conservation Materials. They sent me a sample of Triton XL-80N for evaluation.

Triton XL-80N is a primary alcohol alkoxylate nonionic surfactant manufactured by Union Carbide. Product literature glows: "The best of all worlds... The performance and process properties of nonylphenol ethoxylates, the performance advantages of alcohol ethoxylates, uniquely lower odor, and rapidly and completely biodegraded." Wow.

The MSDS indicates the surfactant is based on a C8-10 alcohol which is ethoxylated and then propoxylated. This gives it the rather daunting chemical name of: alkyl-oxy-polyethylene-oxy-polypropylene-oxy-ethanol. Wow.

Because Triton XL-80N is not based on octylphenol, it is not a xenoestrogen and shouldn't pose any risks of interfering with the body's endocrine system. The MSDS does, however, indicate that XL-80N is somewhat more hazardous than X-100 in terms of acute exposures. Triton XL-80N appears to be more of a skin irritant and poses greater risk of damage to the cornea should it come in contact with the eyes.

The physical properties of Triton XL-80N and X-100 are as follows:

In use, the conservator will find Triton XL-80N dissolves more easily in water. It works well in forming a stable water in VM&P naphtha emulsion and it appears to work well in Richard Wolbers' resin soap formulations. Because of its lower CMC, you might want to decrease the amount of XL-80N by half of that used in X-100 formulae. XL-80N does not, however, produce lamellar emulsion gels at high surfactant concentrations so Richard's 50:30:20 xylene:water:Triton X-100 gel cannot be made with the XL-80N.

The structural differences between Triton XL-80N and X-100 might make a difference in cleaning efficiency in some cases. Triton X-100's structure includes an aromatic ring that probably helps solubilize unsaturated and aromatic components of grime. In a recent conversation with professor Wolbers, he suggested that the addition of a small amount of an aromatic co-solvent like benzyl alcohol should assist the XL-80N in these situations.

Ethafoam: Sheeting, Planks, and Crystals

The Gladon Company is now offering a wide range of Ethafoam^* products as part of their new Preservation Products Division. Foam sheeting is available in 1/8" x 300 ft. and 1/4" x 150 ft. rolls, for $147.99, freight included (continental US only). Planks of Ethafoam, called "Mini-planks" (12" x 24" x 4"), can be purchased in bundles of eight for $56.00, freight included. Ethafoam crystals are a relatively new product, that are produced from milled Ethafoam plank, vacuum processed into closed metal containers, then placed into 8 cubic foot containers. The market for crystals has been to the horticultural industry (suitable as an inert material), as industrial packing and as artificial snow for decorative purposes. One potential drawback is static cling and some of the material is fine enough that it could possibly be inhaled without proper safety precautions. The company believes that the crystals are an exciting new media for archival preservation that may have many unforeseen applications for the museum community.

For more information about Gladon's Ethafoam products contact: Preservation Products (A Division of Gladon Company) 178 West Boden St.,Milwaukee, WI 53207, Phone: 1-(800) 448-6070 Fax: 1-(800) 322-6525

^* Ethafoam is a registered trademark of the Dow Chemical Corporation.

Regalrez 1094: Properties and Uses

Regalrez 1094 is a hydrogenated hydrocarbon resin introduced to conservation by Rene de la Rie, Head of Scientific Research at the National Gallery of Art, Washington. The introduction of Regalrez 1094 and other low molecular weight (LMW) resins came as a result of research into the stabilization of dammar and mastic. Dr. de la Rie discovered that dammar, and to a lesser extent, mastic, could be stabilized with a hindered amine light stabilizer (HALS) in the absence of UV light[1]. In his search for a stable synthetic that could duplicate the optical and aesthetic properties of the less stable natural and ketone resins, he introduced Regalrez 1094, Arkon P90 and an experimental aldehyde manufactured by BASF and not commercially available[2]. The resins Arkon P90 and the aldehyde have been extensively age tested and have been applied to paintings at the Getty Museum[3], Metropolitan Museum of Art[2] and by numerous others in the ensuing years. This technical exchange is an introduction to some of the physical and chemical properties of Regalrez 1094.

Regalrez 1094, manufactured by Hercules Corporation, Wilmington, Delaware, was formulated by industry as a component of coatings and adhesives. Hercules produces at least seven different hydrocarbons in the Regalrez series. By industry standards, it is the highest quality for its type of hydrocarbon resin in terms of UV stability. UV stability relates to the degree of hydrogenation (the higher the degree of hydrogenation, the more stable) and to the softening point (the higher the softening point, the more stable, but any of the resins higher than 1094 are probably too brittle for use as a picture varnish). Regalrez 1094 is 100% hydrogenated and is formulated from pure monomer feed stocks such as vinyl toluene and alpha-methyl-styrene to form oligomers[4]. Arkon P90 is a less clearly defined structure and is not as stable as Regalrez 1094 or the aldehyde but each of these resins must be considered because conservators are such a tiny portion of the market that we cannot influence which resins industry will continue to make[5]. Regalrez 1094 has also been extensively age tested at the National Gallery as a picture varnish to replace the less stable natural resins and ketone resins.

Analytical tests performed on these new low molecular weight resins showed that they have saturation properties and refractive indices comparable to other, less stable, LMW resins such as dammar, mastic, Laropal K80 and MS2A[2]. The new synthetics have slightly different handling and brushing properties than the natural resins. Unlike natural resins, they do not have a polymeric fraction. It is this polymeric fraction that gives the natural resins their characteristic feel and makes them easy to manipulate with brushing. Other familiar synthetic resins (i.e.. B-72, B-67, and the PVA's) do not convincingly imitate natural resins because they have much higher viscosity and conform to microscopically rough surfaces and therefore scatter light[2].

In addition to differences in handling properties between natural and LMW resins, early practical tests by conservators showed the new LMW resins to be slightly more glossy and brittle than their natural and ketone counterparts. Regalrez 1094 has a glass transition (Tg) temperature of 43.8 degrees C, significantly lower than MS2A (54.1) and Laropal K80 (50.8). Arkon P90 and the aldehyde have Tg's of 35.6 and 51.3 respectively. Dammar (39.3) and gum mastic (34.7) have lower Tg's most likely because of their polymeric fractions. The refractive index of Regalrez is 1.519 as compared to 1.539 and 1.536, for dammar and mastic[2] respectively.

To modify the working properties and add flexibility to the resins, Dr. de la Rie age tested various rubbers from the Kraton G series made by Shell Chemical. The Kraton rubbers proved stable when age tested in combination with Regalrez 1094 and the hindered amine light stabilizer Tinuvin 292 up to concentrations of 10% to the weight of the LMW resin[6].

From speaking with technical representatives at Hercules, it was discovered that Regalrez 1094 is added to Kraton G rubbers to act as a tackifier in coatings and hot melt adhesives. Kraton G 1657 and Kraton G 1650 (the ones I recommend for use in varnishes) are styrene-ethylene-butylene-styrene (SEBS) co-polymers. Regalrez 1094 combines with the rubber mid-block to work as a tackifier. Resins that are manufactured to interact with the polystyrene end block phase form non-tacky, hard products[7]. For our purposes, we make a picture varnish by simply reversing the proportions of resin to rubber that are used by industry. The Shell technical information sheet on Kraton rubbers states that SEBS have a "saturated elastomer midblock and thus, have excellent resistance to degradation by oxygen, ozone and UV light"[7]. For our purposes it is strongly recommended that the hindered amine light stabilizer Tinuvin 292 (Ciba Geigy) be added at 2% of the combined weight of the LMW resin and rubber. Even though the rubbers have been tested up to concentrations of 10%, additions of 1.5-3% modify the working properties of the resin substantially. The addition of the rubber can be useful for canvases that have a rough or cupped surface and may need a varnish with more body. The addition of the polymer does improve the brushing properties and provides that resistance to the brush that you feel as you brush a natural resin. A slightly different type of gloss will be achieved when the polymer is added.

My investigation into Regalrez 1094 began with the hope that solvents could be found that would help modify the brushing properties to resemble the brushing of the natural resins. In early aesthetic evaluations of Arkon P90 and the experimental aldehyde, the resins were mixed in Shell Sol 71 which has an evaporation time of 5140 seconds to 90% evaporation and in mineral spirits with evaporation rates between 3200-4600 seconds to 90% evaporation[3]. I have been looking at solvents that evaporate in the 1600-2200 seconds range. Sol 340 HT and MS 146 HT fall in this range and have aromatic contents of less than 0.1%[8]. Practical tests show that these solvents will also dissolve the Kraton rubber additives but that Shell Sol 71 (less than 0.1% aromatic) will not (at least not in a reasonable amount of time). Because Regalrez may have an affinity for hydrocarbon solvents (because they are so similar in chemical structure), solvents that will be 90% evaporated in 1700-2050 seconds evaporate quickly enough to manipulate the surface as you could with a natural resin. SEM studies will hopefully prove or disprove this notion.

Regalrez 1094 has been used with success for the past three years at The Art Institute of Chicago in instances where saturation is needed for canvas and panel paintings, as a means to resaturate synthetics and natural resins that have become dull, and in dilute concentrations in instances where it is appropriate to even areas of matte and gloss. The most common uses have been to resaturate PVA and Lucite varnishes applied in the 1960's and to resaturate natural resins that had become dull, on paintings that were not slated to be fully retreated . Vastly improved surfaces were achieved with spray or brush applications of mixtures of 25-30 g of resin in 100ml of solvent. The resin has also been successfully applied to panel paintings over synthetics or as the primary varnish in amounts ranging from 10-15 g per 100ml of solvent. You can also apply a thin coat of varnish using a cotton ball wrapped in silk. These new LMW resins also have the advantage of dissolving in far less polar solvents than are necessary for natural, ketone, and methacrylate resins. Therefore, they can be applied locally in instances where a tiny bit of saturation or evening of matte and gloss is required. Examples might include 20th century, naive or folk paintings that might be sensitive to most other solvents and that should not have the appearance of a distinct varnish layer. Questions remain about spraying and building up subsequent layers with Regalrez and about achieving matte surfaces. Mark Leonard has suggested that spraying higher concentrations of 35 or 40% may yield matte surfaces[3]. According to product literature, Regalrez 1094 exhibits excellent compatibility with paraffin and micro-crystalline waxes[9].

The type of substrate you wish to varnish will help determine which concentration to select. Regalrez 1094 looks much more like a natural resin when it is applied to a weathered or aged surface than it does on a newer, rich oil film. This varnish can be used successfully without the rubber additive but it is highly recommended that you add Tinuvin 292. It is also important to discard varnish mixtures after three weeks because Tinuvin 292, and resins in general, degrade faster in solution than they do in a dried film. I make small batches for this reason. In some cases the ready solubility of Regalrez 1094 can be a drawback. Built-up spray layers can reticulate and it can be tricky to inpaint on. For paintings that require a great deal of inpainting you may want to use an isolating layer of stabilized dammar or B-72, with a final brush or spray application of Regalrez 1094.

Just as with any new material, varnishing with Regalrez 1094 takes practice. I have found that minor modifications to my working methods allow me to use this resin quite frequently to good effect.

References:

1. E.R. de la Rie and C.W. McGlinchey, "The Effect of a Hindered Amine Light Stabilizer on the Aging of Dammar and Mastic Varnish in an Environment Free of Ultraviolet Light," in Cleaning, Retouching and Coatings, eds. J.S. Mills and P. Smith (London: International Institute for Conservation of Historic and Artistic Works, 1990)160-164.

2 E.R. de la Rie and C.W. McGlinchey, "New Synthetic Resins for Picture Varnishes," id., 168-173.

3. M. Leonard, "Some Observations on the Use and Appearance of Two New Synthetic Resins for Picture Varnishes," id., 174-176.

4 Hercules, private communication.

5. E.R. de la Rie, private communication.

6. E.R. de la Rie, "Polymer Additives for Synthetic Low-Molecular-Weight Varnishes," 10th Triennial Meeting Washington, DC, USA 22-27 August 1993 Preprints Vol. II, ICOM Committee for Conservation, 1993, 566-573.

7. Kraton Polymers for Coatings, Shell Chemical Company, SC: 1757-93, p. 12-13.

8. Shell Hydrocarbon Solvents, SC: 1056-93.

9. Hercules, Technical Information Sheet on "Regalrez 10118,1085,1094,1126 Fully Hydrogenated Hydrocarbon Resins", 1994.

Teflon Floss

W.L. Gore & Associates now makes a polytetrafluoroethylene (Teflon) dental floss, (usually made of nylon), sold as "Glide". The company claims the only additive is a light coating (2% by weight) of natural beeswax, which is food grade and inert, having been triple washed and filtered to remove complex sugars. PTFE floss has potential where strong, smooth, inert filament is needed for object stablization, mounts, packing, etc.

Using Tinuvin 292

Tinuvin 292, a hindered amine light stabilizer (HALS), can be added to varnishes to confer increased stability against photochemically initiated autoxidation caused by oxygen and ultraviolet light.

According to Rene de la Rie, no more than 3% Tinuvin 292 should ever be added to a varnish. The percentage is calculated based on the weight of resin in the varnish and should not include the solvent. The amount of Tinuvin must be measured accurately. The recommended amount of Tinuvin 292 for varnishes are: 2% for synthetic resins, e.g., Regalrez 1094, Arkon P-90, Regalrez 1094 with Kraton G, and 3% for dammar.

Because degradation occurs more quickly in solution than in a dry state, varnish solutions should not be stored indefinitely. Once Tinuvin has been added, varnishes should not be stored for more than 3 weeks. A fresher varnish is better.

The inadvisability of storing varnish means that varnish must be made in smaller batches to minimize waste and disposal expenses. Because Tinuvin is used in such small amounts, measurement is difficult.

A trick used at in the Paintings Department at the Getty Museum is to add the Tinuvin drop-wise to the varnish. By calculating how many drops of Tinuvin weigh 1 gram, small amounts of the stabilizer can be accurately added to varnish.

Mark Leonard, Getty Museum, noted that when Tinuvin is added to dammar or mastic solutions, the varnish will cloud. He pointed out that even when freshly prepared the slight cloudiness does not affect the varnish when brushed. He suggested that if the Tinuvin is added to the varnish two days before use, the varnish will clear. A few drops of benzyl alcohol can also be added to clarify the varnish.

Obtain and read the MSDS for Tinuvin before use. It has an LD50 (oral, rat) of 3125 mg/kg. In guinea pigs it has shown "strong skin sensitizing potential with 20/20 animals sensitized in epidermal challenge." Because Tinuvin 292 is used in Gamblin's Gamvar (see below), they do not recommend spray applications of their varnish. If you do spray a varnish which includes Tinuvin 292, it is imperative that you wear a respirator.

The National Gallery Dammar Varnish Formula

The following information has been extracted from a March 1993 information sheet titled "Stabilized Dammar Varnish" prepared by the Scientific Research Department of the National Gallery of Art in Washington, DC. The information was also published in AIC News (Vol. 18, No. 3; May 1993).

A stabilized dammar can be made by adding 3% Tinuvin 292 to the varnish. When protected from ultraviolet radiation (wavelengths below 400 nm) the varnish proved stable for a minimum of 6000 hours of artificial aging in a xenon arc Weather-ometer. When UV is present, the Tinuvin has little stabilizing effect, but it also has no adverse effects on aging.

Dammar varnish can be dissolved in a mixture of 3 parts Shell Mineral Spirits 135 to 1 part Shell TS 28 Solvent. The varnish prepared with the mineral spirits mixture aged somewhat better than when turpentine was used.

To make a 25% by weight solution of stabilized varnish:

An alternate method for making the varnish when an accurate balance is not available is to make a stock solvent solution that includes Tinuvin and use that solution when preparing the varnish solution:

All solutions should be prepared in small batches and kept for no longer than three weeks.

Sources of Regalrez, Kraton, Tinuvin and Other Varnishes:

For conservators who are loath to calculate percentages and weigh small amounts, Gamvar Picture varnish (Gamblin Artists Colors Co.) is a simpler option. Gamvar is distributed as a kit -- a bottle of solvent with Tinuvin 292 added, and a jar of resin (Regalrez and Kraton G). To use the varnish, add the solvent to the resin. Each kit produces 160 ml of varnish which is said to be sufficient to cover 80 square feet of painting. Once mixed, the varnish has a shelf life of one month, after which time it should be disposed of. Before mixing, Gamvar has an indefinite shelf life.

Gamblin has asked that the specific formulation of Gamvar not be published, but it is based on Rene de la Rie's formulations developed at the National Gallery. To make the commercial product, the percentage of solids has been doubled. Robert Gamblin is happy to discuss the specifics of the formulation with conservators. He can be reached at: (503) 228-9763.

Conservation Materials, Ltd. is now stocking Regalrez 1094, Kraton G-1657, and Tinuvin 292. They also sell the three components as a package. Conservation Support Systems has Regalrez 1094 and Tinuvin 292 in stock. Gamvar is available from Conservation Materials, Conservation Support Systems, TALAS, and many retail art supply outlets.

MS2A, the reduced cyclic ketone resin, is available from Dr. Vincent Routledge; Linden Chemicals Ltd.; 18 Trinity Court, Birchwood; Warrington, Cheshire WA3 6QT; England; Tel/Fax: 01925 850220. Linden Chemicals produces the MS2A in small batches with high quality control specifically for conservation uses. An informative brochure is available from the manufacturer.

The manufacturers of the above mentioned products are: Regalrez 1094; Hercules, Resins Group; Hercules Plaza; Wilmington, DE 19894; (800) 247-4372. Kraton G-1657; Shell Chemical Co.; 3200 Southwest Freeway, Ste. 1230; Houston, TX 77027; (800) 457-2866. Tinuvin 292: Ciba-Geigy, Additives Division; Seven Skyline Drive; Hawthorne, NY 10532-2188; (800) 431-1900. Gamvar: Gamblin Artists Colors Co.; P.O. Box 625; Portland, OR 97207; (503) 228-9763.

From Dorothy Adams

On May 20th, 1994 Douglas Adams was killed instantly in an automobile accident and all of us have been affected; the way one can be affected when someone touches our lives so incredibly.

Conservation Materials will no longer be the same. There is no other Douglas; but Douglas wanted us to go on. So go on we will. Douglas spent 18 years preparing me for this moment. He was a great teacher as many of you know. I am confident that Conservation Materials will continue to be a company that Douglas would be most proud of.

For seventeen years we've known we've needed to serve you with more than just products, and more than just service. You are special people with very special needs and I've spent the last seven months reflecting on what Douglas did for the field of conservation. He worked as a clearing house; as a liaison between one conservator and another, between the manufacturer and the application. We've seen products come and go. We've seen techniques born, incubate, grow old and some even become obsolete. What Conservation Materials has to offer is the ultimate knowledge that the field of conservation needs a supplier that cares to serve the way Douglas Adams cared to serve.

Now, seven months later with Douglas watching over us and spurring me on, I most proudly introduce to you our new BBS system. But I need your help in getting this exciting new system up and running. By the first of the year, with our 800 line functioning as an internet, our computers will be able to talk to each other, work with each other and grow together. You'll not only be able to place your orders directly through your computers, but you'll be able to access our files as well. I want to recreate what you all do so well in your workshops, through your dialogues with each other. The files in the BBS System need to be filled with your papers, your notes, your facts, with what works and what doesn't. Example: you'd like to place an order of Orasol Dyes. You'll be able to pull up our full file, description and price, place your order and then be able to go into our file server and find out all the technical data on Orasol Dyes.

My dream is that these files will be filled with your personal experiences on how best we can all serve the field. Perhaps we will soon be able to come to your studios and film you talking about your experiences with Orasol Dyes (for instance), and most importantly I'd like you to be able to talk to one another, so from around the world you can share with each other your wealth of information. I believe that one of the most special things that Conservation Materials has to offer the professional conservators is out intimate knowledge of how the product and procedure is integral to the ultimate care of your art and artifacts.

I remember so well the early workshops that Doug and I attended; watching the way you shared information with each other. We can never lose sight that the product follows the science. We've always understood that it is an ever growing field, and with your help our new BBS System can serve you in a way that would make Douglas proud. Remember, this cannot happen without you. We need your detailed critiques. We want to grow the way you have always helped us grow in the past. Please call us toll free at 1-800-733-5283. Help me help you.

Lastly, thank you again for loving Douglas. I can't serve the way Douglas did, but this new BBS System will surely help.