STURGEON GLUE FOR PAINTING CONSOLIDATION IN RUSSIA
TATYANA PETUKHOVA, & STEPHEN D. BONADIES
3 RUSSIAN CONSOLIDATION AND IMPREGNATION TECHNIQUE
The following description of a consolidation and impregnation technique that has been used in Russia for canvas paintings with severe craquelure has been translated and adapted from Restavratsiia proizvedenii stankovoi maslianoi zhivopisi by Gorin and Cherkasova (1977).
If the strength of the bond between paint and support may still be in doubt after local consolidation (described in 2.2), general consolidation (where consolidant is applied to recto and verso overall) might be necessary. General consolidation may also be an option in cases where pronounced craquelure is accompanied by quilting of the canvas support.
General consolidation is carried out in two stages. In the first stage, the painting is faced with tissue and dilute sturgeon glue, then removed from its stretcher and restrained in a temporary work stretcher with brown paper. In the second stage the painting is impregnated with sturgeon glue from the verso.
3.1 FACING THE PAINTING AND ATTACHING IT TO THE TEMPORARY STRETCHER
The painting is faced with tissue and dilute sturgeon glue (ca. 0.5–3% w/v, dry weight to water, the concentration depending on the glue). After the faced painting has been removed from its stretcher and its tacking margins flattened, it is ready to be attached to the temporary work stretcher. The brown paper strips should be about 10–25 cm wide. An 8% solution of sturgeon glue (w/v, dry weight to water) with honey (1:1, w/w, dry weight glue to weight honey) [e.g. 100ml 8% glue has 8g dry glue, add 8g honey] is applied to the surface of the painting's tacking margins and allowed to dry almost competely before the brown paper strips are attached. In cases where the tacking margins are in poor condition or missing, the paper strips are attached to the surface of the painting on top of the facing tissue with a 0.5–1.0 cm overlap. In cases where the pictorial edge is in poor condition, these areas should be consolidated with a 1:1 (w/w, dry glue to honey) solution of 5% sturgeon glue with honey prior to facing.
At this point the paper strips are attached to the four sides of the painting. Next the paper strips are adhered to the upper face of the temporary stretcher. A 50% solution of hide glue or a 10–15% solution of sturgeon glue is applied to the upper face of the work stretcher and allowed to dry until just tacky. While the glue is drying, the paper strips are humidified (any technique can be used so long as the amount of moisture is not excessive), except for the edge that will be attached to the temporary stretcher. The humidified strips are then attached in the following sequence: first the short dimensions, then the long dimensions. The paper strips are stretched slightly when they are attached to the temporary stretcher. When the strips have dried they will slightly stretch the painting.
This process is simply a variation of a technique known in the West as the Dutch method, where paste is used instead of glue. Another important difference is that in the Dutch method the paper strips are completely pasted out and attached to the edge of the painting and the work stretcher at the same time. There is no reason, however why a conservator familiar with the Dutch method could not use it equally well in place of the technique just described.
3.2 IMPREGNATION OF THE CANVAS AND ITS RESTRETCHING
Impregnation allows the deep penetration of the glue during consolidation and helps to restore the bond between all structural elements. Consolidation of the paint layers from the surface, only without the subsequent impregnation of the canvas from the reverse, does not always allow as deep a penetration of the glue under the cleaving paint layers. Before this step is undertaken, soil or dirt on the verso of the fabric support should be reduced. The table surface should be cushioned with some type of soft material to prevent any damage to the paint surface when the painting is placed face down.
Impregnation begins with a brush application of solvent to the verso; this application helps to increase the penetration of the sturgeon glue solution through the canvas to the ground. Oil or emulsion grounds can inhibit deep penetration whereas a chalk ground will readily saturate with glue. The choice of the proper solvent to aid penetration is important and depends upon the condition and type of canvas. If the canvas is thin, the application of pinene allows adequate penetration. If the canvas is thick and heavy, xylene, a more reactive agent, should be used.
After the appropriate solvent application, a 1:1 solution (v/v) of 5–6% solution of warm sturgeon glue plasticized with honey is then applied to the verso. At times it is preferable to add a small quantity of xylene, pinene, or ethanol (1:20, v/v) to the glue solution. The resulting mixture is shaken well and quickly applied to the canvas with a brush. The glue is allowed to penetrate slightly; then the verso is gently ironed with a warm iron (80°C) using circular motions. A piece of polyester film is used to isolate the fabric from the iron.
If the painting has severe cleavage, very slight pressure is used when ironing. This method of ironing enables a thorough consolidation and increases the flexibility of the various layers. Ironing should be stopped before the canvas becomes completely dry. At this point the temporary work stretcher is expanded slightly to restretch the painting to its original size and to reduce canvas distortions. The canvas is then allowed to air dry or can be placed under blotters and weights. Additional local consolidation from the recto may be needed. Lining follows if necessary.
3.3 VARIANTS OF LOCAL CONSOLIDATION TECHNIQUES
The warm glue solution can be applied in a variety of ways. In the case of blistering or blind cleavage, a syringe is used to inject the warm glue solution from the canvas reverse. Prior to using the syringe, the area to be treated should be faced with tissue and sturgeon glue. The consolidating solution is injected while the facing tissue is still damp.
Where there are loose and fragile flakes of paint, a Dahlia-type pump sprayer is used to lightly mist the glue solution evenly onto the surface. The misted solution is allowed to dry slightly. This procedure will fix the flakes and prevent them from being dislodged when the tissue is placed in contact with the surface. After the tissue is applied and brushed with more glue, the process proceeds as previously described.
Where excess moisture may be a problem, a piece of tissue is first saturated with the glue solution and then placed on the area to be treated. The area can then be ironed with light pressure until dry.