The first rule of safety when carving stone with hand tools, or using any power or pneumatic tool, is to wear safety glasses. Depending on the type of stone, the chips thrown during carving can be as sharp as glass shards. Your eyes are your most valuable tool; protect them. A quality dust mask is required when carving or sawing some stones, especially those containing silica, like granite. Wear ear plugs to protect against the noise produced by pneumatic tools and diamond saws. Anti-vibration gloves protect hands from the constant vibration of pneumatic tools. Wrist support will help prevent carpal tunnel injury. Keep a well-equipped first aid kit handy.
Planning: There are two basic approaches to carving. The first is to find a stone with a distinctive shape or color pattern that suggests sculptural forms. This approach frees the carver to follow the natural forms within the material. The qualities of the stone itself become a major influence in determining the direction of the sculpture. The second approach is to begin by working out an idea for the sculpture in drawings or by modeling a maquette in clay or other easily worked material. Working out your idea in clay first, when you can add and subtract material, push and twist the forms around, and try different form combinations, frees the carver to develop the sculptural idea without worrying about taking off a chunk of stone that, as his ideas change, he might later wish to have back.
Lay Out: Before you begin carving, look at the stone to determine the direction of the bed, or grain (similar to wood). In sedimentary, metamorphic, and to a lesser extent, igneous stones, the stone was formed by the accumulation of roughly parallel layers of material built up over time. Wetting a sedimentary or metamorphic stone with water will help display these bed lines, often appearing as distinctive color patterns. Stone will tend to break easier when split along these bed lines, like opening the pages of a book. And, like trying to tear a phone book, is more difficult to break (or tear), and breaks less predictably, when the direction is perpendicular to the bed lines. As in laying out a design for a wood carving, with stone you must also consider the direction of the grain to ensure the structural integrity of the parts of the carving. Try to keep the grain running with the length of the design, and avoid thin projections that protrude parallel to the grain. Once you have determined the direction of the bed, check to see if there are any hair-line cracks in the stone that could open up and break off later during carving. Now begin drawing your design on all sides of the stone. Make sure to project the same height and width of each form on to the other sides of the stone.
Roughing out: The quickest way to remove a lot of stone from a block is with the pitching tool. To use this tool, the stone must have a flat surface and squared corners. Place the pitching tool about 1 1/2" from the edge of the stone. Hold it straight up and down, then tilt it back slightly so that the force is directed towards the area you want to break off. With one sharp blow, break off the edge. After removing as much material as possible with the pitching tool, begin to define the shapes with the point chisel. Hold the chisel with your thumb on the outside. It feels awkward at first, but it prevents accidentally striking your thumb with the hammer. Start carving by cutting parallel lines about an inch apart in the stone, creating ridges and grooves. Try not to direct the chisel too deeply into the stone, which will result in pulverizing the stone directly under the point and producing a white blemish, or 'stone bruise.' These white marks require a lot of additional work to remove. Now go back over the same area with a cross-hatch pattern of cuts to knock off the ridges of the first cuts. Place the point so it catches under the ridge and the force pops the chip off. Using this technique, begin defining the geometric planes of the large forms. Work all areas of the sculpture simultaneously so that the entire carving is always at the same stage of completion. In this way you can make more accurate visual judgments as to how to proceed.
A 4 1/2" diamond blade on a grinder can speed up the carving process.
Make a series of parallel cuts about 1" apart. Then break them off with the point chisel.
All of the hand carving chisel shapes - the point, tooth, flat, rondel, etc. - are also made to work with pneumatic hammers. The pneumatic hammer's multiple-strokes-per-second saves time and reduces some of the physical work of carving. Its smooth action can cut a more flowing line through the softer stones. The pneumatic hammer's rapid fire action, when used with with bushing chisels (4 point, 9 point, and cup chisel), make it a very effective tool for shaping the harder stones, like granite. Pneumatic hammers come in different sizes from the large 1 1/4" hammer for roughing out, to the 1/2", or smaller, for fine detail work. Air pressure can also be adjusted for more power or reduced for finer control.
Defining the Forms: Once the large forms have been established with the point chisel, begin refining them with a tooth chisel. The point chisel has left a rough texture of grooves and ridges which can be smoothed down with the tooth chisel. The tooth chisel closely follows the contours of the forms to more accurately define them. Hold the chisel at about a 45 degree angle. A higher angle only bruises the stone; a lower angle just skips over surface. As with the point, try to catch the tool under the ridge of stone to pop it off.
A flat chisel is now used on flat or convex forms to remove the texture left by the tooth chisel. Use the curved edge of the rondel to clean out concave shapes. During this cleaning up stage, you discover if you have bruised the stone and need to do extra work to remove the white marks.
Finishing: On the softer stones, Rasps and rifflers are used for the final smoothing and shaping of the carving. The coarse teeth of a cabinet maker's rasp or round rasp, when used in long sweeping strokes, produces graceful flowing forms.
The smaller rifflers with their varied shapes can get into small areas or complex shapes. On the softer stones, much of the detail carving can be done with rifflers. Final smoothing is done with wet/dry silicon carbide sand paper. On the harder stones, like granite, the final shaping can be done with the 9 point bushing tool followed by the diamond cup grinding wheel.
Polishing: Polishing brings out the beautiful color and pattern of a stone. With the softer stones, continue hand sanding with the wet/dry sand paper under running water. Work through the grits (by roughly doubling the number of the last grit) from 150 grit to your desired degree of polish (somewhere between 600 to 3,000 grit). On the harder stones, I use a pneumatic grinder with a center water feed and diamond pads in an assortment of grits from 40 to 3,000. After you are finished thoroughly going over the piece with a particular grit, let the stone dry. Check to see if there are any scratches or other imperfections that were not removed by the last grit. Mark the blemishes with a colored pencil and go over the area again with the last grit until all the blemishes are removed before proceeding to the next finer grit. If you go through all the grits and have not been drying the stone and checking for blemishes after each grit, when the stone dries you may be shocked to find some remaining scratches. And you have to start all over again from the beginning. Polishing is just plain labor (cn-stonenet.com)