Stone in architecture and sculpture – source material for reconstruction

Stone is the oldest, natural material, which was (and still is) used as both building and sculptural material. The most commonly used for these purposes are: granites, marbles, limestones and sandstones, representing the three main genetic groups of igneous, metamorphic and sedimentary rocks. All of them are permanently being destroyed in result as well of natural weathering as microbiological activity and anthropogenic pollution of atmosphere, known as deterioration. The speed of such decay depends on both environmental conditions and mineral composition of the stone and it can lead to such intensive destruction that conservation may require partial replacement. Smaller damages are refilled with appropriate mineral masses, whereas in case of bigger damages refilling with natural stone is necessary. Professional conservation practice demands the selection and use of the same rock or the rock that is, in so far as is possible, identical to that originally used. It can be done only after previous detailed petrographical studies of the original material. Only then the stone material used for reconstruction will be appropriate and stonework performed properly will not (or almost not) leave marks. In many cases the ancient quarries do not exist and original source material is not available. Then petrographical studies of numerous rock-samples, which are recently available from other existing and/or working quarries, will allow the indication the most similar material. In many cases, unfortunately, the stone used for replacement is not identical to the original but only macroscopically similar. In such a case results might be visible sooner or later. These will be differences in colour, differences in structure and in some cases even crystallization of secondary minerals in the newly inserted fragments.