Once you have used the points chisels and toothed chisels to shape the stone and the flat chisels to even out the surface, it may be time to move onto the abrasive tools. Then again, it may not.
Moving to the next stage too quickly is a mistake that lots of sculptors make, because the process of sculpting takes so long that almost everyone reaches the point of wanting to be finished. Once the basic shaping is done, the next step is to make the surface smoother. You need to get rid of all the bumps and grooves and bruises without introducing new ones. During this stage, the sculptor needs to slow down and be more careful. If you use a flat chisel that’s too small, it may actually dig unintended channels in the stone. If you come too close to a perpendicular surface, you may dent it or dig into it accidentally. If you hold the chisel at a 60 degree angle when you should have been holding it at a 30 degree angle, you can bruise the stone by creating a deep chip or pulverizing several layers of stone as if you’d actually hit it with the hammer rather than the blade of the chisel. You can avoid the vast majority of potential errors by simply slowing down and being more careful.
The more quickly and easily the shaping stage has gone, the less patient you may be when you reach the first stage of smoothing. As you slow down, it often feels like your progress has slowed to a crawl. This is an illusion, you’re just making a different “kind” of progress. If you rush this stage, it will take extra time to fix whatever mistakes you make by trying to hurry through it.
And when progress starts to slow, many beginning sculptors assume that it’s time to move to the filing stage. That too can be a mistake, but frankly, it depends on the stone. Some stones that were hard enough to dull your chisels after a few swings of the hammer actually respond very well to rasping and filing. Other stone is so resistant to abrading tools that you’d might as well be rubbing it with a piece of cloth. These are judgment calls that you need to make when you’re working on your sculpture and you only get really good at it after you’ve done a dozen or more sculptures. Some stone is very hard, but chips and breaks easily and unexpectedly – which may force you into using files and rasps sooner than you would like. Your end goal is usually to have at least a few highly polished areas, even if much of the stone is left rough or textured.
This is where sculpting classes come in really handy, because you have someone with more experience who can answer these questions for you. Is it time to start filing? Is it time to start sanding? It can be hard to tell. I have seen sculptures that are almost unscathed by coarse steel rasps but that respond very well to diamond rasps with much harder cutting surfaces. So don’t be afraid to experiment at this stage. Try different tools until you find one that works. Once again, this is often easier when you are taking sculpture classes and they provide access to a wide variety of tools.
This would probably be a good time to describe the tools, so you know whether it’s a file, rasp or riffler that you’re using.
File: a steel hand tool with small, sharp, straight cut teeth that are angled and extend across the width of the metal surface. Double-cut files are cross-hatched with blades angled two different directions. Files may be have two wide flat surfaces or they could be triangular or round. Some are flat on one side and convex on the other. If the teeth are large and far apart, it is coarse and leaves a fairly rough surface. As the teeth get smaller and closer together it creates a smoother surface.
Rasp: a type of file with individual teeth used for wood and stone work. Wood rasps have pointy teeth and stone rasps have rounder teeth that don’t get dull as quickly. They are often very coarse and leave tiny cut marks on the material you are working on. The teeth do not usually go from edge to edge on the cutting surface. The teeth can be densely packed or widely spaced.
Riffler: a type of rasp with different shaped cutting surfaces. Rifflers often have different spoon or knife shaped cutting surfaces on each end. They are good for detail work and for creating specific effects in certain areas.
Tungsten carbide steel rasps stay sharper and last longer than regular tool or carbon steel rasps. Diamond rasps and rifflers often have finer grain, like 50 or 100 grade sandpaper. While these don’t cut deeply, they often remove material very quickly as don’t get dull as easily.
Chances are you’ll be filing and rasping for days before you get to the sandpaper stage. So it’s worth taking the time to find the best tools for the job. Some soapstones and serpentines contain harmful materials like uranium or asbestos, and even if they don’t, breathing in any kind of stone dust is simply not healthy. So always wear some kind of dust mask when you are rasping and sanding your sculptures.