In the last fifteen, twenty years, modern conservation used to employ various products or chemical semi-products whose properties complied to the requirements of conservators. Only just recently some companies that cooperate with conservators have undertaken the manufacture of products to be used specially to preserve works of art. One of such products is a thermoplastic adhesive known as BEVA 371, developed by Gustaw A. Berger in' the United States. The author of this paper had to his dispodsal a licensed Swiss product. Until today waxen mass was used most frequently to ply up paintings; however, depending on the composition, it has adverse effects upon conserved paintings. One of the disadvantages of waxen mass is a high acid number, then a high coefficient of light refraction and also ability to crystallization (especially in wet and cool interiors of churches), which leads to the desizing of plyed-up paintings. BEVA 371, mentioned above, is deprived of those disadvantages. Its use to ply up paintings in the Monuments Conservation Workshop in Gdansk has been preceded by a number of the socalled blind trials, which gave positive results confirming advantages of the adhesive. BEVA 371 was used to ply up three altar paintings from the 18th century, painted in oil technique on canvas, found in the church at Ostrowiec. The paintings had been preserved before in the 19th century and at that time flour paste was used for plying up but it got mouldy in damp conditions prevailing in the church. This brought about a deplying of the paintings and worsening of the condition of the canvas of subpainting. Because right after the conservation the paintings were to be pu back in the church, it was necessary to use BEVA 371 which had no disadvantages of waxen mass of flour paste. The paintings were prepared for plying-up in the following way: they were taken from frames and a plying-up canvas was removed. The remains of the flour paste were taken from the reverse, while crackings in the facing were protected with paper glued with polyvinyl alcohol. Only then they started putting BEVA 371 on the reverse of the painting and on plying-up canvas stretched on the frame. Just as treated pictures had a smooth painting layer, their plying-up could be done without a special plying-up table. The plying-up was done on a simple table covered with polyester foil on which the painting was put with its face downwards; on it a plying-up canvas was put which was pressed by parts with an electric thermo- regulated iron and additonally pressed and cooled with marbles. As could be found out during the trials and plying-up, the process of gluing can be carried out in a long time distance, after the placing of the preparation on the object. And in this lies a positive property of BEVA 371, namely its thermoplasticity. After the process of gluing had been completed, further procedure was carried out in a traditional way, with only one small modification: to make up the missing parts the putty, based on BEVA 371, with a filler, was used. As has been found out. this adhesive may be employed on a large scale to protect and to glue a painter’s layer and various kinds of plying-ups such as sandwich.
A new variant of plying-up paintings with a high delicate texture proposed by G. A. Berger (Maltechnik— Restauro, I (1980, p. 50— 6 6 ) and which was to eliminate the pressure of foil upon a painting layer has been tested in practice and employed in the Department of the Conservation of Paintings and Polychromed Sculptures in the Copernicus University of Toruń. Instead of Beva 371 recommended by Berger, a water binder (50 per cent water emulsion of Osacryl with 4 per cent methylcellulose as 1 :2) was used giving a tight airproof coat on the back of the plyed-up painting, which made it possible to produce underpressure between the back of the painting and the top of the table. In this lies a difference between that method and a traditional one; moreover, it permits for the plying-up without covering the whole facing of the painting with foil. An additional advantage of the described technique is the possibility to dry up the painting completely during the treatment under a continuous effect of underpressure and increased temperature, which reduces greatly a risk involved in every traditional plying-up on a water binder. This offers also a possiblity to avoid numerous inconveniences of drying the painting with tissue paper under high pressure. The method has been employed in practice to ply up the 18 th-century picture of „Madonna with the Child” .
The article presents the opinion of French conservators, or rather ’’rentoilers”, i.e. people engaged with the doubling of paintings while using the same technique for nearly 300 years and perfecting it all the time. Conservation procedure in France is divided into operations connected with canvas (straightening, local repairs, strip reinforcing, doubling) done by ’’rentoilers” and operations concerning a painter’s layer (removal of varnish and repaintings, retouching), done by restorers. The French double on paste all paintings up to 19th- -century-old-ones according to the principle that this is a well-known material found useful in practice and not foreign to natural substances making the painting. Only paintings from the 20th century are doubled by means of synthetic glues. Wax-resin composition is used by the French very rarely. They think that wax changes a character of the painting; edges of the painting show a tendency to get rounded and the reverse, darkened and ’’greasy”, has an unpleasant appearance, not similar to the original. The article describes one by one stages of a French technique of paste doubling: protection of the facing, consolidation with the reverse, local repairs, reinforcing of a sub-painting by means of sticking a layer of gauze, removal of the protection, secondary protection of the facing, second pressing and fixing the painting onto a loom.