Cutting and Polishing Opals
First you must Chip at the sides of the Opal nobbys to see if they are carrying colour inside, after you have gathered all the Opal you must face each piece and then shape the Opal and then you are ready to document your find before heading off to the cutter which will finish and polish all of your Opals ready for the market place.
Opals : cutting is definitely one of the best skills that a Opal man can learn why he is out on the Opal feels prospecting for Australian Opals, the most important part of cutting is the very first step opal orientation you must learn to cut and orientate Opals, there are many pieces of Opal rough that can be extremely difficult to orientate by practising on a lot of low grade nobbys and then Opal, and if you are lucky enough to have a partner with this skill to sit in and watch him orientate and face as much Opals as possible. Cutting Opal is not particularly difficult naturally some people are a natural at cutting and polishing.
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WORKING OPALS BUY HAND. 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. Background 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 OPALS: 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 Opals, 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 opal stone or two. Don't use your best opal 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.) If takes very little pressure to hold it.. it's almost more of a balancing with a slight gripping.
Now, move the opal 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.
Opal cutting first rub the top of the opal colour, I would recommend good diamond cutting wheels for opals and please use plenty of water to keep the Opal rough cool when cutting opal, when you get close to the opal colour please cut& rub slowly. I would shape the opal gemstones ,you must then putt all your opals onto dobbing sticks and make sure the Opal is sitting Square 90░ to the dobbing sticks and let the opals set firmly over night be for cutting the opals. Next day you must work on a finder diamond cutting wheel some people like to do three stages of different grades of Opal grinding cutting wheels, before they start their polishing of the opals & black opals. Again there are many techniques some Opal cutters also like to use three stages in the polishing process, very important you must not let any contamination interfere with the final opal polishing stages example keep your polishing wheels in a dust free environment unto you are ready to use them. You must then take the Opal's off the sticks and clean them with warm water after a final check of the Opals ,find the scales weight each Opal or black opals placed them in the individual plastic bag and price the opals.
Cutting Opal the most important procedure by far is orientating the Opal rough because if this stage is incorrect then you will lose large amount of opal colour and opals, there is nothing you can do to fix the problem all the polishing and cutting will not put the opal colour back. This procedure takes many years to learn and the only way to learn is to rub down as much low grade inexpensive rough opals as you can possibly fine . And please remember black opal is different to Crystal opal and boulder opal is different again learn your particular type of Opal and remember just because you understand one type of opal if you go out on to a Queensland boulder opal feel to buy boulder and you have specialised in orientating and cutting crystal opal for example then you really need to change your approach and thinking slightly.
CUTTING OPAL Equipment White base opals-220 diamond - can use 100 grit to flatten back. Crystal opals - 320 or used 260, front and back. Andamooka jelly opals, Yowah opals& some other opals - 180 grit. Boulder opals - Iron stone matrix - 180; opal on matrix, worn 220 or 320. Flat lap vs. wheels. All new diamond wheels or flat-laps should be broken in with black potch or agate before using on opals. Trim saw .010 or .012 thickness of blade, depending on experience.
If experienced use 4 inch .004 inch - less opals is wasted. Explain use of saw blades on trim saw. Opal Classes Crystal opal rough much more expensive than "potch & opal color" or white base. Crystal opals mostly all color with only a little potch or unwanted inclusions. Crystal opals harder, more brittle than white base opals. White base (or potch & color) less color than crystal with potch intermixed with color. Usually 5? hardness on MOHs hardness scale. Crystal opal being harder than white base must be cut with more patience, finer diamond wheel. Can be 6 plus on MOHs hardness scale. Crystal opals are easier to orient. Less chance of fractures or unwanted inclusions in rough. Can take more liberties cutting white base. Doesn't shear off usually. There are chances of fractures in rough.
You will get less opal gemstones out of white base or potch & color. Routine for cutting and cabbing opals Check edge around all of stone. Grind off thin edges, cracks, and potch, anything that won't be part of finished gemstone. This step will make orienting opal gemstones easier. Orient gemsstone. Decide which side will be top, which side will be bottom. Your cuts should be in same direction as the opal color lines. Flatten bottom. Orient bottom with color lines. Finish shaping gemstone. (Free form or calibrated.) Smooth opals Crystal opal, black opal bottom edges of gemstone. Dop gemstone. When dopping gemstone make certain the gemstone is level on all sides of dop stick. If not level cutting will be difficult. Make first cut entirely around the opals. Distance of cut to the bottom of opal stone should be the same all around stone. Amount cut off depends on height of opal dome. Make second cut if necessary. On high domed opal stones second cut will be necessary. Cab or dome opals. Use twirling motion for getting right slope on opal gemstones. Smooth sides, coordinate with dome. Note: Adjustments of sides of opal stone may be necessary when cutting opal stone (to remove fractures, potch or unwanted inclusions from your opals or black,Crystal opals). Don't forget to re-smooth bottom edges of stone after removing from dop stick, after polishing stone. Polishing your Australian opals black Crystal 600 grit diamond (paste or 6oogrit polishing wheel).
This grit will remove most small scratches or pits from the opals. Sometimes it is necessary to go down to 325 grit. If it doesn't smooth opal stone it might be necessary to re-cab with diamond wheel or flat-lap. Many times fractures or imperfections' didn't show until 600 grit is used. 1200 grit polishing diamond. (Paste or diamond polishing wheel) This grit can remove very fine scratches from the opals. ** If it doesn't, you will have to go back to 600 grit or 325 grit. .After; 1200 grit used stone should have no scratches or imperfections. 8000 grit. (Paste or diamond polishing wheel.) This is a polish and will not cut opal gemstone. 14,000 diamond grit. (Paste or diamond polishing wheel). If cerium oxide on leather is available try going from 8,000 to cerium oxide. If not available use the 14,000 polish. Do not use a finer grit as the oil suspending the finer grit may be absorbed by the opals. Remove opals Crystal blacks from dop stick with single edge razor blade. Clean back of opals of dop wax, etc. with worn 600 grit belt. Recheck edges of back for smoothness. A twirling motion should be used for all pre-polishing and polishing. Fine scratches can be fractures or can be caused by diamond wheel used in cabbing stone. If you have broken wheel in by cabbing a couple agates you shouldn't have protruding diamond problems.
Telephone:+61 731033023   Skype name: midnight507