Free-forming Opal By Hand
Article by Carol Bova
There are 5 ways to free-form opal:
- On the wheels of a regular cabbing unit, silicon carbide or diamond
- With a Dremel or Foredom flexible shaft device and changeable bits
- With the sponge blocks that have diamond mesh of various grits on one side
- On a piece of glass with a slurry of grits
- With sandpaper by hand, glued to wood blocks or to wood dowels of various thickness.
Let' say though, that you want a totally low-tech, non-electric approach, and don't have access to the sponge blocks or the various levels of grits... that leaves the sandpaper method.
- Get a series of sandpapers in various grits, 100, 220, 320, 400, 600, 1200, 14,000 or something around that level. If your local home improvement store doesn't have them, an automotive supply will for refinishing work.
- Have a small bowl or container for water for rinsing the stone.
- Get a small amount of #2 cerium oxide for polishing. An ounce lasts a long time.
- And something to put the cerium oxide on: a piece of old blue jeans will work, or you can buy a leather or felt polishing pad intended for a cab unit and use it by hand.
Know it is a very slow process, and requires a lot of care in cleaning between stages, especially in the hand-powered methods. One piece of lower level abrasive at a higher level can ruin a day's work by leaving an ugly gouge.
When you change grit, you wash the stone in clean water, change the water and clean out the container you're using to keep the stone wet and last, put away the lower grit material, (separate paper bags are a good idea to keep from contaminating a higher level sheet -- and the paper lets the sheet dry off between uses) and wash your hands before moving onto the next step.
THE MAIN RULE OF CUTTING OPAL: LOOK A LOT, CUT A LITTLE you can't add back what you've taken off! Before you begin, identify the color bar, (If you have access to Paul Downing's book on Cutting Opal, he does a good job of explaining this.) You need to know where you want to get to before you start cutting.
Shaping the Stone
(If you have access to a water cooled trim saw, it's best to trim off the worst of the potch because while it can be done with sandpaper alone, it can take a lot of time too!) Using the 100 grit, take a small piece of the entire sheet, and rub lightly against the stone to remove the worst of the potch and determine the rough shape of the final stone. Don't 'scrub' in only one direction -- use little circles or a combination of back and forth, then side to side strokes.
Doing that, you will keep the grinding fairly even, and avoid creating deep gouges that can lead to sub-surface fractures. (These are the nasty little breaks that won't show up until you get to the pre-polish or polish stage... then they break off, leaving a concoidal chip right in the worst possible place. That means you have to go all the way back to the 1st or second step, and clear up the damage, then work your way all the way back to where you were when the chip flaked off.)
Dip the opal in the water occasionally to keep it wet, and rinse off the sanded off material. Overheated opal will chip much more easily. When you have a shape you like, clean everything up, and start again at the next higher level.
Do this at every level of grits...make sure that you have removed the larger scratches before going on to the subsequent level. When you have the exact shape, and all the scratches are removed, and the surface has a slightly polished look to it, you are ready for the polishing.
Put some cerium oxide powder on the polishing material. Then mix it into a slurry with clean water. (Slurry is wetter than a paste, wet enough to move freely, but not wet enough to drip off.) You can add more water if it's too dry after you start working it. Rub the opal with the polish in every direction, until you have a smooth, and lustrous polish. At the very end, allow the polish to go almost dry, but still watch for heat buildup which can damage the stone. A little warm is good, too hot to hold isn't.
I know some of this is vague, but it's not an exact science. You'll start to get the 'feel' of it after you do a stone or two. Don't use your best material for the first try. Use a low grade piece and plan to destroy it in the process. Make gouges so you know what they look like, and see first hand why you won't want them in your finished piece. You'll find how slippery a wet opal can become, and learn to find it on the floor by the sound it makes when it bounces. Much better to do these the first time on a piece that isn't your pride and joy!
If you have a cabbing unit, you can use it for opal... freeform or calibrated. I personally cut without a dopstick using a Pixie at the Opal Society Workshop. I'll try to describe how I hold the stone: Put your thumbs together... tip to tip, then do the same with your index fingers. (You can curl the rest of your fingers into the palm). Now, remembering that position pick up a piece of opal, and hold it so that instead of touch finger to finger, thumb to thumb, each finger is touch a corner of the opal, holding it more by pressure inward, forefingers at the top, thumbs at the bottom (rather than by gripping it between thumb and forefinger as you would when you pick something up.) It takes very little pressure to hold it.. it's almost more of a balancing with a slight gripping. Now, move the stone up and down, end to end, side to side, in small circles, and notice how little effort is required.
Then you take the stone to the wheel... and this is the fun part! Using your four fingered hold, rotate your hands down, so your fingers move up and the stone is the highest point. Push up the stone against the wheel while balancing it and holding it lightly from underneath. Then you go ahead and use the wheel to do the work for you. A little trickier at first, but infinitely faster!
You'll never overheat a stone that way, because you can feel it all the time. You do have a higher risk of losing control and having it fly away, but practice does help on that.