Set-up of a methodology to evaluate the consolidation of archaeological waterlogged wood veneered in ivory

Abstract

This work describes how a conservation method making use of aqueous solutions of lactitol and trehalose (9:1) was chosen to treat several elements of wood furniture veneered in ivory carved in bas-relief and preserved in waterlogged condition. These elements were discovered during the excavations carried out in Villa dei Papiri, the most famous of the luxury villas of Herculaneum. The approach described was based on a dual evaluation. It was carried out: (a) on probe wood specimens produced in the laboratory capable of simulating both the impregnability by consolidants and the deformation of decayed waterlogged wood; (b) on one archaeological element belonging to the original furniture, representative of the material to be treated. The probe specimens produced in the laboratory were artificially degraded by placing them in contact with the brown rot fungus Coniophora puteana, in order to obtain a material of variable decay, similar to that of the original archaeological furniture elements. Three experimental factors were considered when treating probe specimens: (a) the type of substrate, (b) the initial and final consolidant concentration and (c) the drying regime.Three types of substrates were considered: specimens covered with a polycarbonate sheet to simulate the ivory veneer and wrapped in gauze; specimens only wrapped in gauze; and naked specimens, that is, with no obstacles for consolidant penetration. Considering consolidant concentration, the probe specimens were impregnated by full immersion, increasing the concentration of lactitol/trehalose in four combinations: from 15 to 50%, 15 to 60%, 30 to 50%, and 30 to 60%. Last, three drying regimes were considered: 50 °C in an oven, 30 °C/35% RH and 20 °C/65% RH. Results showed that probe specimens whose impregnation started with 30% consolidant in the solution and finished in 60%, and dried under 30 °C and 35% RH exhibited limited volume variations after drying equivalent to those obtained by drying at 50 °C. Drying conditions were important factors in the success of the entire treatment process. As was consolidant uptake, in relation to the extent of decay of the archaeological material. Moreover, the presence of the physical barriers simulating the existence of the ivory veneers and gauzes did not disturb the efficacy of the treatment, as long as sufficient time was given to allow the water-consolidant exchange process to be completed. In the end, the treatment conditions selected on the basis of these probing tests, that is, start with initial concentration of 30%, final concentration of 60%, and drying at 30 °C/35% RH, showed to be successful for treating the representative element of the archaeological furniture.