engleski

Protection of medieval tombstones (Stećci) with ammonium oxalate treatment

Since 2013 Croatian Conservation Institute has performed research and preliminary conservation works on medieval tombstones (stećci) on the archaeological site Crljivica near Cista Velika in Croatia. During the project, tombstones from several sites in the region of Cista were analysed for provenance study and for protection of stones. Stone characterisation was performed using mineralogical-petrographical analysis on different tombstones and surrounding quarries or rock outcrops. Approximately 80% of analysed stones from tombstones were determined to be biomicritic limestones ranging from wackestone to floutstone (according to Dunham classification). They were all determined to be from the upper Cretaceous. Other analysed tombstones were determined to be dolomites. Some of the surrounding quarries did show the same type of limestones. Concerning the protection of tombstones, one of the main goals was to create a protective layer of artificial calcium oxalate on stone surface through the reaction of ammonium oxalate with calcium carbonate. In order to establish the most effective way of achieving such kind of protection, research included laboratory testing and in-situ testing. Ammonium oxalate was applied on the stone by poultice (24 h), brushing method (1, 2 and 3 hours) and total immersion (24 h). The method of total immersion of stone provided best results, both in laboratory and on site.

medieval tombstones (stećci); stone deterioration; calcium-oxalate; ammonium oxalate; limestone

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