Volume 9, Number 1, Jan. 1987, pp.9-12

Technical Exchange

Insect Pest Identification Services

The Common Insect Museum Pests Study Collection has been assembled by Dr. Carlton Koehler, an entomologist at U.C. Berkeley. The collection contains adults, immature insects and frass of common insect pests according to a list supplied by Jim Druzik. The Getty Conservation Institute would be glad to provide identification services free of charge. Send pest sample to Jim Druzik for initial identification and processing.

LACMA Experiments with Cleaning Systems

The Paintings Conservation studio at LACMA has in the past few months experimented with some of the cleaning systems devised by Richard Wolbers (Senior Paintings Conservator, Winterthur Museum): 1) enzyme gel formulations for removal of oil overpaint or protein-based materials, 2) emulsions which combine organic and aqueous phases in gel-like solutions using non-ionic detergent and 3) soap solutions composed of compounds molecularly similar in structure to natural resins and prepared in aqueous solution.

Interest in these cleaning methods was generated by seminars which Mr. Wolbers gave at the Getty Museum this past summer and by his two subsequent brief visits to LACMA when we discussed his systems as applicable to paintings in our collection. Coincidentally, Ginny Rasmussen joined us in September as our intern from the University of Delaware bringing with her first-hand knowledge of these methods.

The following paragraphs briefly describe some of the experiences we at LACMA have had with the cleaning systems.

One painting which was particularly well-suited for treatment with enzymes was a Hans Bol Landscape of 1578. This is a Tuchlein grossly overpainted with oil colors. Lipase gel attacked the old overpaint but left the original aqueous paint untouched. Nevertheless, caution was required since the gel could "overclean". It could not be manipulated to clean evenly. It was important to stop the process at the right moment to only thin the overpaint. Remaining overpaint was then evenly removed using organic solvents.

Of the different compounds under consideration here, the xylene emulsion has had the widest use in our studio. A thickly painted oil on canvas by Paul Kelpe Composition 309 (1932) provides an example for which the gel was particularly more successful than traditional methods. The coating, a thick, yellowed, natural resin varnish, was difficult to remove because of the character of the impasto. The xylene emulsion as a gel could set on the surface for a predetermined length of time dissolving the varnish. Thus the solvent had time to penetrate into the deep crevices of the paint where varnish is most difficult to reach.

Paint layers on the Kelps were easily blanched with traditional solvents but the xylene emulsion having a moderate rate of activity was easy to control. Also, little friction was required to remove already disintegrated varnish.

The paint layers of Archille Gorky's Mojave (1941-42), thickly coated with B-67, were very sensitive to solvents, even water, and to friction. It was necessary to find something which would just thin the varnish. Xylene emulsion allowed to set on the varnish for a certain few minutes did just that. Again, it was the solvent held in suspension in the gel which allowed for greater control.

Xylene emulsion did not work on the synthetic varnish covering our Portrait of Mlle. Y.D. (1913) by Jacques Villon. Unfortunately, all solvents, including xylene emulsion, caused blanching of the paint films. Our Senior Research Chemist, JOHN TWILLEY, looking at solubility parameters, helped us to decide on an organic solvent mixture which allowed us to thin the varnish with no blanching and no need for revarnishing.

The resin soaps have been tried on a good number of paintings but nothing successful can be reported. Compounded for removal of natural resin varnishes, the soaps did not stand up to the thick, oxidized examples at hand. Here we feel that failure was due in part to our lack of experience in the use of different proportions and/or bridge solvents in the basic solutions.

In the interest of experimenting with what seems to be an attractive alternative for cleaning paintings, we are as a matter of course testing these new systems on most paintings which require cleaning. Enzymes, soaps and emulsions are not necessarily a substitute for other cleaning techniques. However, more and more we are discovering their effectiveness where other systems have failed.

Chinex Clear Glaze

Bradywicks of Santa Barbara is experimenting with "Chintex Clear Glaze" as a medium for adhering gold powder onto fills on porcelain. By brushing or spraying the lacquer onto the fill and allowing it to dry for thirty minutes, the gold can be dusted on to create a matte surface. The technique is still being refined, but the results so far look promising. "Chintex Clear Glaze" is manufactured in Great Britain and distributed by Conservation Materials.

Syloid 169

The Antiquities Conservation Department of the J. Paul Getty Museum has recently begun evaluating matting agents added to acrylic coating for bronzes.

Our preliminary findings show that the best results were obtained with SYLOID 169, a synthetic amorphous silica that has been surface treated with a hydrocarbon-type wax. The SYLOID 169 was added in varying percentages to a 3% solution of B-72 in toluene. After testing, the appropriate mixtures were airbrushed onto a bronze surface previously treated with Incralac. The desired effect was reached when the shiny surface was altered sufficiently to achieve an aesthetically pleasing matte finish. SYLOID silicas are used in a variety of industries as well as for such purposes as in: anti-caking, flatting, thickening and suspension agents, adhesives, and lacquers. The extent of their application in the conservation field has yet to be investigated. Additional information on SYLOID 169 can be obtained from the Davison Chemical Division, WR Grace and Company, P.O. Box 2117, Baltimore, Maryland 21203.

Humidification Hood

Designed after the humidification hood which was first demonstrated at the 1986 Chicago A.I.C. meeting, Peter Carlson has built and modified this hood for the Paper Conservation Laboratory at LACMA. The hood fits snugly atop the custom vacuum suction table, also designed by Peter Carlson. Made of non-marring Lexan with a stainless steel frame, the hood has four hinged access ports and utilizes a sophisticated pulley system to hoist it off the vacuum suction table for easy storage above it. There is also a double filter system for incoming air at the top of the unit. An ultrasonic humidifier has been permanently attached to the hood to provide a fine consistent mist when the hood is in place and a separate ultrasonic humidifying unit has been adapted as a hand tool for spot treatments. We are still in the process of working with the designer to perfect the design as we learn about it through use. Anyone interested in this system is welcome to call for details.

Precautionary Note on Disposable Propellant Canister Use

Some years ago while dissecting what I felt to be a particularly ingenious handheld propellant sprayer in order to see how it worked, I became aware that it contained an oily residue which could be of concern if used in certain treatment applications. Only recently I became aware that paper conservators were using a similar disposable propellant canister for spray applications of deacidifying reagents on works of art. Procedural questions had also been raised about the cause of yellowing which accompanied some, but not all, methods of application of the same reagent. It quickly became clear that these canisters also possessed oil in the propellant reservoir. While the oil did not seem to have caused the observed yellowing in this particular case, conservators should consider that staining may be caused by the unknown contents of such propellant systems. Such problems are easily identified. A canister of the propellant should be completely discharged, without anything attached to the aspirator, into a clean white cloth. Normally this procedure will require several pauses in order that the can may sufficiently rewarm to volatilize all of the propellant. The idea is to catch any non-volatile residue on a material where it is readily visible. If the propellant chills sufficiently so that the liquid propellant runs through the cloth; then slow down so that the liquid will not carry the evidence away. When all of the propellant has evaporated and any frost has dried up, inspect the cloth carefully for residue or a "tide line". After the canister has returned to room temperature and retains no pressure whatsoever it may be safely cut open with tin-snips. At this point a little effervescent liquid may remain as propellant, which has dissolved in any non-volatile residue, escapes. Liquid which persists after this stage could persist on or in the art object if it had been expelled. Typically little droplets of straw colored oily residue can be found in the canister.

To avoid speculation, the brands of canister in which I have observed small amounts of residue are listed below. I want to emphasize however that these are the only ones which I have examined and they are not necessarily any better or worse than others one might find. Their manufacturers might, in fact, be able to recommend another model which is suitable for more stringent requirements. I have not inquired. As in any similar case, the conservator is ultimately responsible for determining that the materials used are suitable for the work in question. Both models [Preval (TM) - Precision Valve Corp., Yonkers, NY and Crown Spratool (TM) model #8011 - Crown Industrial Product Co., Hebron, IL] utilize a chlorofluorocarbon (a "Freon") propellant. I do not know if C02 or hydrocarbon propellants incorporate the same residue. I do not know if the "oil" serves some intentional purpose or if the amount is consistent from can to can. It may be a higher molecular weight byproduct of the propellant synthesis. "Oil" content is quite small in volume by comparison both to the propellant and to the reagent that one could apply and for some applications should not be a problem.

From an environmental point of view one would wish to substitute a non-fluorocarbon propellant model. Hydrocarbons are, of course, flammable but if the reagents being sprayed are flammable anyway (alcohol solutions, varnish, etc.) this shouldn't increase the risks appreciably.