Reversible Modification Of Flexural Rigidity On Dry Archaeological Leather From Wet Anaerobic Burial Sites: An Herbal Method Irma

Abstract

This work is based on a treatment reported in the article “Über der Weichen trockengefallener Alkohol und Formalinpräparate, Herbarblätter und von Tapagewebe” in Der Präparator from 2001 by Klaus Weichsler and co-authors. A series of experiments were performed to investigate the described effect of cherry laurel leaves and the compounds emitted therefrom upon flexural rigidity of dry archaeological leather from wet burial sites, which upon uncontrolled drying becomes rigid. To aid interpretation or to ease stress and strain on the material, it is often desirable to modify the flexural rigidity of the leather to allow for the object to be reformed. A review of current leather treatments which modify flexural rigidity: immersion, humidity chambers and infusion with humectants followed by freeze drying, indicates that some dry archaeological leathers would not withstand these treatments due to induced collapse and cross-linking of collagen fibres. Treatment with cherry laurel leaves (Prunus laurocerasus) has been proposed as an alternative method, but there is a general lack of literature on the treatment and no explanation of the working mechanism of the treatment. Considering the time and constrained resources, a limited number of methods were selected to first evaluate the effect of the treatment on dry archaeological leather, and then clarify the mechanism of the treatment. An apparatus to measure the flexural rigidity of leather was designed and constructed. Results from this instrument were used to demonstrate that; a) the treatment depends upon emission of volatile compounds from the crushed leaves; and that b) benzaldehyde and water are the active compounds in the treatment. An experiment comparing the effects of a matrix of treatments: 1) chopped cherry laurel leaves in contact; 2) chopped cherry laurel leaves in noncontact; 3) benzaldehyde + distilled water; and, 4) 4-Methoxybenzaldehyde + distilled water was conducted by measuring changes in: flexural rigidity, pH, surface colour, weight, length, width, thickness and evaluate other attributes such as visual appearance, touch/texture, workability with respect to both before and immediately after treatment and also with respect to treatment reversibility through elapsed time following treatment. This experiment indicates that all treatments work in a similar way, but to different extents, and that the presence of an aldehyde + moisture is required for modification of flexural rigidity. Benzaldehyde with water was found to be the most effective treatment. The results also indicate that the treatments are reversible within an acceptable time frame with the changes in the above measured properties returning to their original values within 48 hours following treatment. Benzaldehyde with water has the added benefit of not involving the emission of HCN(hydrogen cyanide), as is the case when cherry laurel leaves are used, which is both an acute toxin and a potential hazard for the leather