How Hard is that Stone to Carve?

People often wonder how hard a stone is to carve. Of course, there are two meanings to this question. One being, how challenging is it to carve anything? Most people seem daunted at the prospect of the subtractive process of carving (as compared to the additive process of building up a sculpture from clay, for example.)

Today I'm going to address the other meaning behind that question. Literally, how hard is that stone? Some stones are actually pretty soft and can be scratched with your fingernail, making them about 1-2.5 on the Mohs scale. Soapstone is a good example of this soft stone. Soapstone comes in a wide variety of colors, depending upon where it is found. It is easy to carve. Again, it scratches quite easily, so keeping it looking good can be a challenge, especially if it will be handled a lot.

The Mohs scale is the scale of hardness for all stones.

Pretty much everyone knows that diamonds are about as hard as they get and it takes very special tools (and skills) to work with diamonds, a 10 on the scale. Most stones used for sculptures fall somewhere between those two extreme--between 4 and 7 on the scale.

The numbers are deceptive, they really don't go up in an easy progression. Each number reflects a significantly harder level. Granite and some marbles are quite hard and are typically worked using diamond or carbide tipped tools. Other stones use a basic tool--and are a lot easier on the body to carve when using handtools.

So if you have the proper tools, even a hard stone on the Mohs scale can be carved. If you have the wrong tools, carving that same stone will be next to impossible.

One of the challenges is that since stone is a natural medium, the stones are not pure...I've carved many stones in the 5 range on the Mohs scale that had bits of iron and quartz in them. Quartz is officially a 7 on the scale. When I ran over the iron and the quartz bits I totally ruined my standard file. When using a carbide or diamond file on the softer stone it is overkill. Getting both components to be even level and looking good is a challenge and an awesome result when done well.