Choosing stones

The most important is to get a sound stone. It means the stone should be free of cracks and unsound areas. To test the stone, take a hammer and hit the piece so that it can ring. If it sounds like steel (“ring, ring”) with a clear sound, your stone is good. If the sound is a “toc toc” or “cloc”, the stone can’t resonate well because of a crack. You should either leave the piece and test another one or try to investigate to see where is the crack. Its location it important. If the crack is at the edge, it will have to come off sooner than later. If it is right in the middle, you’ll have to divide the stone in 2No. pieces. If you don’t separate them, glue them. I don’t like this option as it might be a waste of time working on a bad stone which could result in a broken sculpture later anyway.
It is important to know that some stones don’t sound at all. Some alabaster pieces might sound ok but can be cracked because of the nature of the piece. Experience is the only way to know how dangerous a crack is. But usually, an open crack means it is a dodgy stone, if it is a closed crack (not through the stone) it can be ok.
After the hammer test, a close look at every sides of the stone should be done. Search for cracks, discolouring and staining (especially oil contents which penetrate the stone permanently. They can’t be cleaned by a chemical agent. Remove the stained material until a clean stone is emerging). Use water to pour onto larger blocks. If the water gets in the stone and shows a zone which is getting dryer than the rest, there is a crack. In any case, the stone should be clean (meaning free of dirt) for close inspection.