The use of PVA (AYAB, Union Carbide) as a new inpainting medium and varnish for the restoration and conservation of Old Masters was introduced to the profession by Mario Modestini in 1953.
It was a revolutionary method, extensively tested, which was since accepted by many leading museums and private conservators worldwide. When Union Carbide discontinued its production of AYAB, many professionals began searching for an acceptable substitute. It seems that several researchers, working independently of each other, found Mowilith 20 (Hoechst Chemical Co.) to be such an acceptable substitute
(1). Having worked with the AYAB inpainting medium since its introduction to the profession, G. Berger developed a formula for adapting Mowilith 20 which most closely resembles AYAB
(2). G. Berger's Inpainting medium is sold in concentrate form containing 35% solids. For inpainting it should be diluted in ethanol (1:4), to make a 7% solution of PVA (5 times the quantity sold). This formula stays permanently reversible in alcohol and/or water of low alkalinity.
1. De la Rie, E.R., Private communications, 1990.
2. Berger, G.A., Inpainting Using PVA Medium", Preprints of Contributions to the IIC 13th International Congress in Brussels, (1990).