I have been making a bowl recently and thought I’d show you the different stages in the process. Every stone is different, and my working techniques and choice of blades will vary according to what works best. It’s often a case of just trying things out, and seeing what cuts and abrases best.
With this Caithness stone, I initially used a multi purpose 12″ disc cutting blade. I then found a 5″ granite flush cut blade worked much better than the marble/limestone ones. Then a combination of cup wheels, spiracut semi-flexible silicone carbide discs, and velour/velcro sanding discs, then hand sanding with wet and dry paper. A big portion of tenacity, concentration and elbow grease is needed. It’s pretty hard stuff……but lovely, and satisfying.
I designed the bowl before starting, and made a scale drawing of the section, in order to calculate the largest possible chamfers I could remove to start forming the desired curve for the underside of the bowl. The two lines that describe the chamfer are scribed onto the stone, one on the side and one on the bottom.
It’s really important that the first chamfer is very carefully and accurately ground off, and is straight, in section, not curved, as otherwise you’ll never get as much material off as you want, you’ll end up with a chunkier, heavier bowl. You must work to the scribed lines, making a straight cut between them. Eventually the curve is found, once you have taken off a series of incrementally smaller chamfers and roughly rounded everything off.
The inside is more tricky as you’re kind of working blind and trying to take enough material away, but without digging in too much. I don’t want this too deep, as it’s a birdbath, and also I’ll be drilling into the bottom for a stainless steel dowel.
Now the stone is brought in for finishing by hand, which is when you can feel it taking shape, and also get rid of all the mini chamfers and kinks in the grinding process. Wet and dry paper is used, from about 60, 80, 120 grit dry, then 120, 240, 320 600 with water.
Here are a few pictures of the finished stone, prior to the final rinse and oiling it. I chose to leave the rough natural top surface as a nice contrast to the smooth underside and interior.