Nové postupy při ošetření geologických vzorků postižených degradací disulfidů železa (pyrit a markazit)
Boris Ekrt, Michal Novák, Jan Sklenář, Zuzana Gazdová
Iron disulphide degradation poses a continuing threat to geoscience collections. Pyrite and marcasite are especially susceptible to oxidation, the products of which eventually totally destroy the specimens. Only a few efficient methods of acute conservation have been invented. Ethanolaminthioglycolate (ETG) in an alcohol solution is usually employed. ETG converts the degradation products into soluble complexes, allowing them to be washed away. However, the method is chemical- and time-consuming, and the results are rather disputable in most cases. Another ordinary method is based on the effect of ammonia gas, which neutralises the acidic degradation products and transforms them into less hygroscopic compounds. There is just one such method that has been widely employed: the Waller method, using a mixture of ammonium hydroxide with a humectant as the source of ammonia. Two new remedial conservation methods have been developed and proven during the preparation of comprehensive methodology for treating material containing degradabile disulphides. The effectivity and other parameters of the new methods were tested and compared with conventional ammonia-gas methods. The first newly developed method, using dry ammonia gas treated under high pressure, was both the fastest and most effective. The second new method, using gaseous ammonia emanated from ammonium carbonate or hydrogen carbonate, was evaluated as being the most affordable, easy to use and safest method.