ATT KRITA ELLER INTE KRITA – DET ÄR FRÅGAN En undersökning kring kritning av hällristningar i Tanum, Brastad och Lundby med fokus på bevarandeproblematik

Abstract

Based on the results obtained from this study, no traces of chalk can be seen with the naked eye or through chemical analyzes of samples from rock carving premises that were chalked at least 4 years ago. Chalk consists mainly of calcium carbonate (CaCO3) and/or calcium sulphate dihydrate (CaSO42H2O), these can be extracted from the soil or produced by chemical means. The type of chalk that may be used on rock carvings in Västra Götaland region is only natural chalk, this can be Bologna- or Champagne chalk. Other types of chalk may contain unknown additives, dyes and adhesives. These should not be used on rock carvings as the outcome can prove harmful to the rock. High levels of calcium sulphate dihydrate, which are found in gypsum, blackboard chalk, sidewalk chalk and Bologna chalk, can also be harmful as the material can adhere tightly to the slab and risk clogging of the pores of the rock. If liquid cannot be transported in and out of the rock, the risk of weathering of the stone increases. Chalking has, in this study, proved not to be as harmful as expected but should still be avoided. We still do not know how far the chalk has moved into the granite pores, or the long-term effects. Chalking as an archaeological documentation technique entails a human impact on the rock which today can be largely avoided using digital methods.