Comparing sulphamic acid to acetic and formic acids for the preparation of large mesozoic marine reptile fossils, and a method for monitoring residual acid and salt removal following acid preparation

Abstract

Chemical preparation is an important technique in palaeontology that uses a dilute aqueous acid solution to remove calcareous matrix from fossils, but which leads to the evolution of salts as a by-product. Acid preparation is usually undertaken using formic and acetic acids, whereas sulphamic acid has only rarely been considered. Sulphamic acid is a strong acid, with many industrial uses, but which has fewer health and safety concerns, and produces fewer irritant fumes, than formic or acetic acids. Three comparative procedures were undertaken to understand the action of sulphamic acid in relation to formic and acetic acids, using calcareous matrix from Colombian (South American) large Mesozoic marine reptiles. The results of these procedures indicate sulphamic acid acts in a comparable manner to formic acid, and more rapidly than acetic acid, in terms of rate of matrix removal. Afourth procedure investigated the removal of acid and salt residues following sulphamic acid preparation of a Colombian large Mesozoic marine reptile fossil, a process essential for the long-term survival of any acid prepared specimen. The fossil was immersed in type 1 deionized water, and increasing electrical conductivity was used as a proxy for ionic leaching. The results imply the preparators 'rule of thumb' of soaking a specimen in water for three times the length of time spent in the acid solution, is inadequate to ensure satisfactory removal of acid and salt residues. Although tested on a specimen prepared using sulphamic acid, the technique for post-preparation ion removal is equally be applicable to all fossils prepared using sulphamic, formic or acetic acids in aqueous solution.