These occur but rarely and in laying down the work can usually be avoided. If a stone contains many it is useless for litho work. Rust marks and brown stains occur but apart from the difficulty of seeing, the work on these stones, they do not seriously interfere with it. Perfect stones are very rare, particularly in the larger sizes and this has led to the cementing of thin slabs of good quality together. So perfectly is this done that a close examination would be found necessary to find it out.
Stones vary in color from pale buff to dark grey.
Usually grey stones are hardest and most even grained. This together with the faults mentioned tend to keep up the prices of stones. Stones must not be stored in a damp place. Decomposition is likely to set in which may penetrate below the surface. The gum on the face of the stone will also turn sour and acid.