CCI2014050744

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Collagen shrinkage temperaturę was chosen as an indicator morę directly linked to the depolumerization reaction catalysed by metal ions. This is the temperaturę at which the crystalline structure of the collagen fibers is destro-yed (Florian 1984), and would naturally be lowered if the crystalline structure had already been disrupted by the depolymerization of the collagen molecule. Collagen shrinkage temperatures were measured by suspending samples and a thermometer in a beaker of water at room temperaturę, and slcwly raising the temperaturę of the whole constantly stirring to keep the temperaturę the same throughout the beaker. The temperatures at which the samples began to curl and at which they were completely curled were noted, and averaged (table 4). Three to four trials were run for aech type of sample. The tests consistently showed a signifi-cantly higher shrinkage temperaturę - as much as 6C higher - for those samples protected with the cupferron, even for the 17th century leather which had already degraded to the point where the collegen shrinkage temperaturę was at least 30C lower than for new calf leather. Samples treated with the emulsion without cupferron showed no significant diffe-rences from untreated samples.

Tensile strength was also measured for all of the samples. The readings were widely disparate within the groups, however, so no conclusion can be drawn from these tests (table 5).

The success of the cupferron emulsion in protecting against lcwering of collegen shrinkage temperaturę, however, is significant enough to recommend this emulsion as a treatment for leathers that are threatened by deterioration from the metal ion catalysed reaction.

ACKNOWLEDGEMENTS

To P. Hallebeek, T. Stambolov and J. Mosk of the Centraal Laboratorium in Amsterdam for their assistance in develo-ping research methods, and to P. Hallebeek also for his instruction in the use of the atomie absorption spectrophotometer; and to H. Porck of the Kbninklijke Bibliotheek in the Hague for his assistance with testing samples for tensile strength.

BIBLIOGRAPHY

1.    Deasy, Clara L., (1967). Degradation of collagen by metal ion-hydrogen peroxide Systems. I. Evidence for a free radical-catalyzed depolymerization mechanism. Journal of the American Leahter Chemists Association 62, 258-269.

2.    Deasy, Clara L., (1969). Degradation of collagen by metal ion-hydrogen peroxide systems. III. Effect of conditions and of added salts on the degradation of collagen by the cupric ion-hydrogen peroxide system. Journal of the American Leahter Chemists Association 64, 345-357.

3.    Florian, M.L., (1984). Conservation implications of the structure, reactivity, deterioration, and modification of proteinaceous materiał. In: Protein Chemistry for Conseryators, American Institute for Conservation, Washington.