The Roman Hammer and Hardie
For cutting stone the hammer and hardie (sometimes spelt hardy) has been in use for 2,000 years. It is used to cut marble and other hard stones into a wide range of sizes to create the tesserae (tiles) needed for mosaic work.
Its advantage over using nippers in cutting stone is that it is the weight of the hammer which does the cutting thereby alleviating the stress on the wrists you get with using tile nippers. With practice you can even cut tesserae down to 1mm in size.
Using the hammer and hardie is a very straight forward practical skill and you should be able to gain a basic level of competency with 2 weeks of practice.
Your Cutting Position
The most common one people use is to have either a full size block or a smaller one on a table / small stool to the side of them while they are working from a stool of chair. The block needs to be at a height so that when you hold the hammer over the hardie, ready to use then your elbow should be at 90 degrees.
The block is, if you're right handed, on your left side and vice versa. This is so that when you cut you have to twist your upper body less. I will admit though that I use it a lot on my left side (I'm left handed) and find I move less to make the cut.
The main thing is to ensure that you have a relaxed seating position and you do not have to stretch.
Using the Hammer and Hardie
Remember, it's like a pair of pincers, the blades of the hammer and hardie should line up with each other in exactly the same way.
1. Hold the handle about of of the way down.
2. Your elbow should be at about 90 degrees, a right angle.
3. Move your wrist, not your elbow or shoulder, these should stay relaxed.
4. Hold the marble onto the hardie, make it easy for yourself any straight edges on the marble place those on the hardie and / or upwards (the part that the hammer will strike)
5. The hammer blade does not need to cover all the marble, half way across is fine. You are not so much cutting the marble as sending a fraction across the stone.
6. Drop the hammer onto the marble; you'll get to know the correct sound. They make a different sound if you have the blades connect; this is not good as it will blunt them.
The only time you need to use your whole arm is with hard stones such as granite. This is a very tough material that requires more effort and it is not generally used for mosaics.
You will notice the different sound the hammer makes when it is cutting correctly. Do not be too worried if you find you hear the hammer and hardie striking each other. You will 'soften' your strikes with practice.
If you find your piece of stone just is not cutting then stop, check your cutting position, if that's OK then generally you need to move the hammer further off the stone.
Positioning the marble for cutting
You are not cutting the marble more sending a fraction across the stone so you do not need to have the whole of the line you want to cut underneath the hammer blade.
Position the marble on the hardie just off the center. When the blade of the hammer comes down it will only need to strike part of the stone to make the cut