CCI2014050737

-68-

Discussion

Impregnation with silicone monomers, followed by in-situ polymerization, proves promising if suitable ratios of polymer to plasticizer are established. However, impreg-nations with these products might suffer from difficulties in removing them from the leather later on. Although the polymers are water-soluble, Chemical reactions between the reactive epoxide group in Tg or the aminę group in Ta and the tanned collagen fibers of the leather could render them insoluble. On the other hand, just these possible Chemical reactions may serve to give extra support to very deterio-rated leather.

When impregnation with polyethyleneglycols is chosen for the conservation of waterlogged leather, molecular weight grade 400 is preferred because it gives the best visual aspects to the treated leather at all concentrations.

From impregnation experiments using PEG400 at different concentrations, followed by various prefreezing conditions, it may be stated that:

1.    Prefreezing is not necessary with 50% PEG400, because a shrinkage of less than 2% is obtained.

2.    For very critical applications or very deteriorated leather, prefreezing at -80°C of 50% PEG400 impregnated leather might be the method of choice; the only drawback of high PEG concentrations is the slightly moist touch at 55% RH and 21°C.

3.    Impregnation with 35% PEG400, followed by prefreezing at -80°C represents the best compromise: good visual aspect, dry touch, and limited shrinkage (about 1%).

4.    20% PEG400 is too Iow a concentration to prevent consi-derable shrinkage (5-7%) in all circumstances.

Theoretically, thawing of the solid phase present in the object during lyophilization should be avoided throughout the procedurę to prevent the collagen fibers from collaps-sing. However, the liquid phase is always present after pretreatment at room temperaturę even though lyophilization causes a drop to -10°C sińce this lcwered temperaturę is still above the Et of PEG/water mixtures. When no cryopro-tector is present, lyophilization has disastrous results (shrinkage 13%), but at 50% PEG400, enough polymer is present to keep the fibers "wetted" and supported.

BIBLIOGRAPHY

1.    Ganiaris, H., Keene, S. and Starling, K., 1982.

A comparison of sane treatments for excavated leather. The Gonservator , Vol. 6, pp. 12-23.

2.    Morris, K. and Seifert, B.L., 1978. Conservation of leather and textiles from the Defence. J. Am. Inst. Conservation, Vol. 18, pp. 33-43.

3.    Rosenqvist, A.M., 1973. Konservierung von Nassleder durch Gefriertrocknung. Arbeitsblaetter fuer Restau-ratoren, Vol. 2, pp. 13-14.

4.    Elmer, J.Th., 1980. Die Gefriertrocknung von Nassleder-Bodenfunde aus dem Bereich der Archaeologie. In "Konser-vering og restaurering af laeder, skind og pergament", Konservatorskolen det Kongelige Kunstakademi, pp. 212-225.

5.    Miihlethaler, B., 1973. Conservation of waterlogged wood and wet leather. Centre International d'etudes pour la conservation et la restauration des biens culturels, et Comite de I'IGOM pour la oonservation. Edition Eyrolles, Paris, pp. 25-72.

6.    Rumyantsev, E.A., 1958. A method of preservation of wet leather. Kratkie Soobshcheniya o dokladach i polevych rabotakh, Instituta istorii materal'noj Kul'turi,

Mosccw, Vol. 72, pp. 100-102.

7.    Lehmann, D., 1983. Hinweise zur Lederkonservierung. Maltechnik, Vol. 3, pp. 204-207.

8.    Schmitzer, W., 1973. Alte Lederarbeiten, Ihre Pflege und Erhaltung. Arbeitsblaetter fuer Restauratoren, Vol. 2, pp. 15-32.

9.    Peacock, E.E., 1984. Mass reconservation of archaeologi-cal leather, a case study. ICDM Committee for Oonser-vation, 7th triennial meeting, Copenhagen, preprints, pp. 84.18.19-84.18.21.