Opal Cutting Tips

Let me preface this by saying there are many, many methods of opal cutting that are effective and will result in a perfectly acceptable finished cabachon. I have developed some techniques, over the years that have worked well for me. I would like to share my personal methods with you in the hopes that it will save you some time and frustration (and also produce gems you will be proud of). You may want to, almost certainly, expand on these techniques and develop a method of opal cutting that works well for your style and types of equipment.

Basic Non Motorized Equipment

Some of this is a repeat of the dialogue on our home page, but I would like to go into this topic in a little more detail. When I was 24 years old and stationed about the aircraft carrier USS Saratoga (1969-1973 for any salty sea dogs who may have been in the same position) I had some free time on my hands and was homesick for my lapidary equipment in Richfield Minnesota. I wrote to my parents and had them send me an unused 8" 220 grit grinding wheel, various grades of wet/dry sanding cloth, some dop sticks, some dopping wax, and some tin oxide polishing powder.

I ordered some opals from W. H. (Bill) Walker. He was an opal-dealer in the late '60's and early 70's. I heard some very colorful stories about Bill Walker in Coober Pedy, from the old time miners and buyers. He made several opal-buying trips to Australia in the 60's and 70's and is quite a legend.

I would study the stones carefully for maximum fire and direction and decide which side would be the back, then grind the back of the stone to make it flat and attach the stone to the dop stick for better control. I would carefully dop the stone by heating the stone gently (to make it adhere better to the dopping wax) and fix it to the melted dopping wax (on the dop stick) forming the wax onto the opal base in a smooth symmetrical fashion.

I would use the flat side of the grinding wheel, by hand to flatten the stone back and rough shape the stone once it is on the dop stick. It is a slow process and I didn't use much water...just enough to keep the dust down and clean the wheel occasionally...it was a dusty job. Final shaping was done using the 220 grit wet/dry sandpaper and then going to 600 grit paper (final sand and pre-polish with the old 600 cloths) and then polishing on a piece of old felt blanket with tin oxide. It was very labor intensive, but the control was amazing and you seldom cut through a fire layer!

Motorized Equipment with Diamond Abrasives

Sorry, but I don't have any new Genie's, Pixies or Titans (although they would make wonderful opal and gem cutting machines...maybe some day).

I have converted several machines, which I purchased new, (several years ago) from silicon carbide abrasives to diamond abrasives. It really was quite a hit or miss proposition to find the right combinations in diamond abrasives vs. silicon carbide and come up with a workable solution to give a decent polish and not cut too fast or too slow.

First of all I use my Hi-Tech 8-inch unit to flatten the back of the stone (once you have studied and oriented the stone). I use a 180 grit for rough grinding for the back and then go to a 600 grit wheel to give it a partial polish.

I then use 220 diamond grinding belts or wheels for rough cutting and shaping the tops of the larger stones. With smaller stones (less then a carat) you may want to use a 320 grit sanding belt for rough shaping. Small stones cut very fast and before you know it there is nothing left...so beware. After rough cutting is finished I go to a 320 grit sanding belt (I personally like Raytech True Circle belts). I then go to a 600 grit belt for some final shaping and sanding (and to put a small bevel around the perimeter of the stone base...to prevent chipping when setting or to compensate for any extra solder the goldsmith may have left around the inside of the bezel) and then to a 1200 grit belt to get rid of the 600 grit scratches.

For pre-polish I use either an 1800 grit belt or a 3000 grit belt. Most of my wheels on the cabbing unit's are expanding drums to make switching of belts simple and economical. They either (1800 grit or 3000 grit) seem to give a great pre-polish. I then wash the stone and dop sticks well to remove any contaminating grits and it's off to the leather disc with tin oxide for the final polish. I am old fashioned as many people use 14,000 grit diamond and 50,000 grit diamond...I guess I like my tin oxide on soft leather discs. And as long as you keep the wheel wet, with a little mist from a spray bottle, there is really no heat buildup. It gives a great polish. Note: December 30, 2005...I broke down and bought an 8", 50,000 grit diamond sanding disk, for the end of my 8" unit, and have been using it for an extra bright final finish on opal cabs (after polishing with a tin oxide/Linde A mixture). I have to admit it DOES give a great final polish to my opal cabs and I really can tell the difference...the old adage is wrong...you can teach old dogs new tricks!

6-inch TC-6 trim saw...careful of the thin blade...it cuts flesh!

Sawing

For sawing I use my newest piece of equipment (2 years old) a Diamond Pacific TC-6 trim saw equipped with a MK-1000 6 inch by .006-inch blade. I purchased the saw through Kingsley North Lapidary supply (whom I recommend for equipment and general lapidary supplies...they are timely and helpful, and courteous). The blade is very thin so you don't lose much opal) so watch your fingers and it is also stainless so rusting is not a problem. I like to use Lube Cool 4800 for a saw coolant...a 16 ounce container goes a long way in a small trim saw especially when diluted 10 to 1 for sawing purposes.

A Little About Dopping

I used to use dopping wax to hold my stones on the dopping sticks, but after cracking a few heat sensitive opals (and having a few fly off of the stick and smash into little pieces) I decided I needed a new approach.

Use wood glue and fingernail polish when thoroughly dry to attach stones to dop sticks.

First I tried sodium silicate or water glass (as a glue) but found it too thin and difficult to remove. Just for the heck of it I tried white wood glue. It was thick and held the stone in place with never letting go. The only problem was it was not waterproof. I solved that problem by adding a coating of clear fingernail polish over the well-dried wood glue. I placed the stone with a drop or two of glue on the stick and centered it carefully) and placed the stone and stick vertically in a flattened pad of children's modeling clay and let the stone dry overnight. I then coated the glued portion with the fingernail polish and ten minutes later I was ready to cut. This takes some extra patience when waiting for the glue to dry overnight, but with a $500.00 (or more) stone in the balance it may well be worth it.

To remove the stone I use acetone or fingernail polish remover to remove the fingernail polish and set in a glass of water overnight and the stone usually just falls off the dop stick in the morning. Be sure to clean the back of the stone with soap and water to remove any extra glue or you may re-glue the stone to a tabletop.

If you have any questions about techniques, equipment or opals in general don't hesitate to call. Evening hours 406-651-4947 (8:00 AM to 9:30 PM Mountain time). We like to visit about opals in general and are for the most part, very friendly, so don't hesitate to call! You know that good old Scandinavian heritage and hospitality...ya hey der, you know by golly.

Treating fractured opals

This is an e-mail I received from a good friend and a customer on treating fractured opals.... I cannot personally vouch for the procedure because I have not tried it but he swears by it and I have seen some amazing pictures of opals that he has treated in this manner.

Hey guys, this works!

Here is my procedure on Opticon for opals. This is done without the use of a vacuum machine and the results are very good! First I cut my opals to the desired shape with my opal blade (.006 diamond blade). I also use my saw blade to rough dome my cabs. This is done very slowly. Most people will grind the dome with their first stage of grit. After you have roughed in the stone and it is dry, place the stone or stones in a pint mason jar. It is more cost efficient to do several stones at once.

Fill the jar with Opticon (resin) to just cover all the stones by 1/8-1/4 inch over the stones. Place the jar on a coffee machine burner, like an old Mr. Coffee machine. Turn on the machine like you would if you were making coffee and cover the pint jar with a doubled piece of foil (do not put lid and ring on). Cook the opals for 6-8 hrs. After you are done cooking the opals remove the opals from the heat, take off the foil and pour as much of the Opticon out of the jar as you can, use oven mitts...that jar is mighty hot!!!! After you have gotten the hot resin out, put back on heat for a minute or so. Once you've done this procedure a few times you can empty out the resin pretty fast and don't have to return it to the heat. The whole point is to keep the stones hot.

After you empty the resin, place the lid and ring on the jar and tighten. Set aside for 8 hrs. When it cools the lid will pop and create it's own vacuum. I usually start in the morning and then let the jar cool over night. After it has set for 8hrs or more, open up the jar and remove the opals one by one, cleaning off the resin with a paper towel. Use gloves (surgical or latex) when doing this. You do not want to get this stuff on your hands!!!! Get another pint jar out for the hardener, ring and lid also. Place opals on a piece of foil and take hardener bottle and apply it to the stones (don't use a whole lot but the stones have to be wet). Get a pair of chopsticks or shishka-bob sticks and roll the stones so every part is wet with hardener. Take the jar and run it under as hot of water as your sink puts out, (pre heating it. Don't get the inside wet). When the jar is fairly warm, place the opals (on the foil) down in the jar. I normally shape the foil first to fit down into the jar. Place the jar on the coffee machine burner and cook 2hrs, covering it with foil. About 1 hr into the cooking, get your chopsticks and roll the stones in the hardener at least once. It is very important that you do not breath the fumes; hold your breath when you do this.

After about 2 hrs, remove from heat and place lid and tighten ring on jar. Set aside for 6-8 hrs, the lid should pop or suck down on this also. After it has set 6-8 hrs, open up jar and remove stones (with gloves on) and wipe off any remaining hardener. Let stones sit for a day or until they don't feel sticky. Dop up your stones and proceed to polish them. Keep in mind; the Opticon only penetrates so far into the stone, 1/16-1/8 inch maybe. So the less gouges in the stone the better. I have yet to replace a ring on either jar, they keep sealing (10 times so far on both rings).

Opticon is an optical grade polymer resin, clearest of clear. It can save a stone that normally would have to be re-cut or used for chip inlay...crushed. There is nothing wrong with using Opticon but you need to state that the opal has been treated with it. Paul Downing has a good view on morals of the use of this product. Some people will treat their high-end stones with Opticon to stabilize the stone from possible damage in the future. Opticon will protect or save you from future grief. Opals are so awesome and I if you can keep one whole or save a fractured stone all the better. You just need to state the fact that you treated the stone. It doesn't harm or affect the beauty of the opal and can only be detected under a microscope and special lights. The stone will "fluoresce" or glow a reddish color under magnification, otherwise it is undetectable by the human eye, even with a loupe. This procedure does not make the stones invincible but they will last a whole lot longer, be less fragile, and much more stable. P.S. I don't treat every opal I cut, just problem ones.

Hopelessly addicted,
Jeff Norman

An delightful example of a carved Lightning Ridge stone. Photo courtesy Len Cram, carving artist unknown.

Introduction to Opal Carving and Contouring

Here is a text that was designed for to be a lesson plan for my opal cutting classes and eventually turned into a magazine article for Rock & Gem magazine. Hope it is of some use in fine-tuning your opal cutting skills.

On one of our buying trips to Australia, Darlene and I were lucky enough to attend a two-day opal carving course taught by Stuart Jackson, a master opal carver and cutter at the TAFE on Hutchison Street in Coober Pedy. The brief synopsis presented here is loosely based on that carving class with tidbits thrown in from personal experience. Keep in mind this is not the only way to carve opal, just one method that has proven comfortable and that works well for me.

EQUIPMENT: MOTOR UNITS

For opal carving and general jewelry work, I prefer the small, motorized hand pieces that fit comfortably in your fingersÖalmost like holding a pen. ìMarathon Micro-Motor Systemî is available from Rio Grande and Gesswein. This unit has a 35,000rpm motor, foot control and runs on either 220V or 110V. It uses a small, powerful motorized hand-piece that fits comfortably in your hand. Price is the drawback with the Marathon unit. as it is listed at US$395.00. A very good alternative is the Foredom SR Flex Shaft System which is also available from Rio Grande. This unit has a forward /reverse selection that is useful to keep debris from flying into your face. It has a collet-based hand piece (44T) that is not as convenient as a chuck-based hand piece (#30). These flex shaft units run from US$175.00 (SR) to US$400.00. Have a look at a couple of catalogs and decide which units are best for you. Rio Grande can be reached at 800-545-6566, Gesswein at 800-243-4466, Kingsley North at 800-338-9280 and Contendi at 800-343-3364 . When carving, I use two units with a different cutting point in each hand piece to decrease the time required to change points.

A marathon Micro-motor power unit and handpiece with felt polishing buff attached.

EQUIPMENT: CARVING ABRASIVES AND POLISHES

For roughing out the opal I like to use the small, nickel-plated, 150 grit diamond points available in 20/30 piece assortment sets with many different sizes and shapes. They are very inexpensive and last a long time on the relatively soft opal. The inexpensive points are sold, in most cases, in coarse grits. Lasco Diamond Products (800-621-4726) has a great assortment of different grits (and shapes) of diamond points available. The big advantage in using finer diamond (400 & 600 grit) point wheels is that deep scratches can be smoothed out much quicker than using the Cratex wheels. On the Mohís hardness scale opals rate 5.5 to 6.5 while quartz gems rate 7.0. After I have roughed out an approximate design with the diamond points, I switch to course Cratex wheels of various shapes to finalize the carving design. Then I am ready to begin the smoothing process. I store the wheels in labeled individual organizer boxes to avoid cross contamination. Use one box for each different grade of abrasive. I work my way down from course to medium to fine and then extra fine. The Cratex wheels are soft and lose their shape in a relatively short period of time. But fear not, they can be used down to the nub by reshaping when spinning against the cut on an old ìbastardî file. This name is not a reference to the character of the file. After the Cratex wheels have done their job and there are no more deep scratches seen when finishing with extra fine (check carefully with your Optivisor to avoid repeating this process after you have reached the polishing stage and it becomes very obvious), I switch to diamond compound on small felt wheels of various shapes. Apply the compound directly on the felt buffsÖno extender fluid needed. After finishing with extra fine Cratex I switch to 1200 grit diamond. I then progress to 3000 grit, 14,000 grit and then to 50,000 grit. If you have some ëperfectionisticí blood coursing through your veins, go on to 100,000 grit and see if it makes a difference. Cleaning the stone and your hands well between diamond grit steps is essential to a good polish. Be sure to keep your felt/diamond buffs of different grits, separated from one another, by storing in labeled individual organizer boxes.

An assortment of very inexpensive, diamond abrasive carving points.

INTRODUCTION: WHY CARVE?

Since opal carving or contouring is so labor intensive, I usually reserve opals that show no promise for traditional cabachon cutting for this procedure. There are several reasons that opals may not be suitable for traditional cabachon cutting. The most common reason is that the shape of the opals may be very irregularÖthick on one end and thin on the other or thick on the ends and very thin in the center. Another reason found in very ìtop gemî grade material is that you may need to contour the stone to save every carat of material available in the rough stone. This may allow a creative gem cutter to convert an opal that was estimated to finish out into a $1,500 gem into a stone that sells for $2,000. One more reason to carve an opal is to create an object of art. This art object may have a structure completely different than and not dependant on, the shape of the stone or available fire pattern, and the stone is used only as a medium for the final project (this wonít be covered in this article, but it would not be difficult to utilize these techniques to perform this function). Another reason is to be able to shape a stone to follow an irregular or undulating fire layer, to cut a concave face on a boulder opal seam or to remove an irregularity or flaw (such as a sand pocket) from the middle of a stone by only removing a small amount of opal. Mastering these techniques is relatively simple and allows a gemcutter much more freedom in selecting rough and allows one to greatly improve the final yield from a parcel of opal!

Keeping your polishing buffs organized in seperate boxes of like grits, will prevent cross contamination.

TECHNIQUE: STUDYING YOUR OPAL

After I have selected a piece of rough, I study the stone to determine how best to begin carving. Keep in mind factors such as sand pockets, irregular surfaces, undulating fire lines, directionality of the fire and a final design that is pleasing to the eye. When you have exposed the ìheart of the opalî by grinding away any opaque surface layers, begin planning on removing any extra potch or sand pockets while planning for an ìeye pleasingî final design that uses the fire lines or fire patterns to enhance the beauty of the gem. Yes, what you are thinking is correctÖthis is the hard part! Some of my favorite shapes are geometrics, swirls, waves and shapes that ìsuggestî natural objects without too closely resembling them. This will remove the burden of trying to exactly reproduce plants, animals or sceneryÖsomething that may require the skills only available with formal art training.

Beware of the metal rivets on the tops of the felt buffing wheels. These rivets can deeply scratch your opals.

TECHNIQUE: CARVING

Begin grinding away the colorless skin of the opal using your diamond bits or cabachon cutting lapidary wheels. When you have exposed the ìheart of the opalî begin planning on removing any extra potch or sand pockets while planning for an ìeye pleasingî final design that uses the fire lines or fire patterns to enhance the beauty of the gem. Yes, what you are thinking is correctÖthis is the hard part! Some of my favorite shapes are geometrics, swirls, waves and shapes that ìsuggestî natural objects without closely resembling them. This will remove the burden of trying to exactly reproduce plants, animals or sceneryÖsomething that may require the skills only available with extensive art training.With a shape or design in mind begin grinding with the small 150 grit diamond plated points. Keep in mind that the ball tips and the cylinder shaped tips are used the most so several kits of the same shapes are needed. They are inexpensive and at the time of writing this article, varied from US$7.55/ kit (20 piece) to US$10.45 (30 piece). These points cut fast and can be used wet or dry. I know that sounds like blasphemyÖdry cutting opals, but there is very little heat build-up with the small points. I have yet to have a problem. Dry grinding opals releases silica dust into the air and inhaling silica dust causes silicosis. Wearing a dust mask would be a very good idea! Also, eye protection is important as the Cratex wheels are not designed to run at 35,000rpm and may fly apart if you accidentally use too much speed. Motor operated hand pieces (or flex shaft units) have a bad habit of getting away from you due to the effects of centrifugal force and friction. You may end up grinding an area on your project that was not meant to be ground. To prevent this from happening, you must keep both hands resting on and well supported by the bench or bench pin. When you have roughed in your design to the approximate shape, change to the coarse Cratex wheels and remove the scratches produced by the 150 grit diamond points. You will also be finalizing the shape of your contoured or carved opal. Continue on with medium, fine and extra-fine Crates wheels removing scratches from previous wheels and fine tuning the shape. Inspect your work well with magnification between steps, to be sure that scratches from previous Crates wheels have been removed. Keep in mind that you donít want to use high speed with the Cratex wheels or they will come apart. Another ìgotchaî with Cratex wheels is they produce a lot of heat, so if you are cutting dry, check your work often for heat build up and keep the speed down. Before progressing to the diamond compound prepolish/polish stage, give your work area a general clean up. Dust away any abrasive from the Cratex wheels and wipe down your workbench with a wet cloth or paper towel to remove all debris. Wash your hands and your work!

Keeping both hands firmly supported on the table will prevent accidently grinding an unwanted area. Use a towel to cushion writs and forearms.

TECHNIQUE: POLISHING

Now begin pre-polishing with 1200 grit diamond. A note of caution: Some of the felt buffs have metal rivets exposed on the tops. If this metal should come in contact with your opal it will deeply scratch your work and make you very sadÖbeware!! Continue on with 3,000 grit diamond compound on felt buffs, then onto 14,000 diamond and then to 50,000 for a high polish. Inspect CAREFULLY with magnification between each step to be sure you donít have deep scratches remaining. As I said earlier, you may try 100,000 diamond for the ultra super high gloss polish. OKÖthis is the moment of truth. Put on your Optivisor (or equivalent) and relying on good lighting, closely inspect your work. At this point scratches will stand out on the highly polished surface. You may need to repeat a few steps using diamond grit to remove scratches (or even to the Cratex wheels). Donít feel bad. This is pretty much routine and part of the process, because it is very difficult to see scratches until you reach this stage. At least that is what I have been telling myself all these years! Opals are one of the most beautiful of Godís creations! After spending a day cutting gem grade opals I can still see the beautiful multi-colored flashes of fire when I close my eyes at night. These delightful stones are unknown millennia in the making. If we can find a way to gently transform more of this precious stone into finished works of beauty, instead of dust in the bottom of a grinder pan, it is surely time not wasted.

Everything you need to resurface a worn diamond belt.

REFURBISH YOUR WORN OUT DIAMOND BELTS

I just hate to throw away perfectly good diamond sanding belts with no useable diamond abrasive remaining. The belt integrity seems fine but the diamond abrasive is gone. With diamond powder so inexpensive, I thought with a little ingenuity, I could make a good working belt out of an old worn out belt. And I did! I believe this procedure would work for Nova wheels as well.

Enough bragging. Letís get down to it. I clean the belt thoroughly with acetone. Read the warnings on the acetone can, it is dangerous stuff. Place the belt over an expanding drum or old grinding wheel (just to give it a solid backing) and suspend on a dowel between two stacks of books or boxes so the belt/wheel hangs free and can be rotated easily by hand.

I use Hughes Epoxy 220 made by Hughes Associates out of Wayzata MN. The epoxy hardens without being brittle and mixes well with the diamond powder. I use the small plastic measuring cups for liquid medication doses that are available in drug stores, for measuring and mixing. Mix 1teaspoonful equal amounts of hardener and resin in the small cup. Then dump in a 5 carat vial of the appropriate grade of diamond powder and mix thoroughly again. This is not 5 Minute Epoxy, so you have plenty of time to mix. Mixing is very important here as small lumps of abrasive will lower the effective grit of your abrasive and cause the finer abrasive grades to cause scratches. MixÖMixÖMix.

Apply the epoxy-diamond mixture to the belt smoothly using the disposable acid flux brushes pictured below. Apply in a thin coat so there are no lumps or thick areas. The epoxy sets up in one hour (hardens in 8 hrs) so you must keep rotating the belt every few minutes to keep mixture from running on the belt. A heat lamp or warm desk lamp greatly reduces hardening times, but donít get the belt too hot. One teaspoon (and 5 carats diamond) is enough for 1-6in X 2in belt. I usually have a little left over. Ten carats is about right for a 8in X 3in belt. I would toss the used brushes so you donít cross contaminate although they can be cleaned with acetone and reused for the same grits or coarser.

I recently finished a 600 grit belt and it cuts faster than a new belt just out of the box. I have an older 220 grit diamond-sanding belt, that I refurbished 2 years ago, and it seems as though it will never wear out.

NOTE: Even if a thick coat is applied uniformly, it tends to run, giving you a bumpy belt (though they are certainly still useable, I have a bumpy belt that has been used for several years and is finally beginning to smooth out as the diamond wears off). I would try 2 thin coats (1/2 the diamond powder per coat) rather than 1 thick coat, to give your wheel extended life.

Cutting Ethiopian Welo Opal

The new opal deposit in Ethiopia, in Wello Province in the north of the country, is producing spectacular crystal opal displaying very bright play-of-colors in a variety of patterns. The opals in this new deposit, discovered in 2008, are nodule-like stones in an unusual variety, where some stones resemble top Mexican fire opal with excellent play-of-color, others resemble subtle dream-like stones from Brazil and many resemble bright crystal opal from the Andamooka opal field of South Australia. Itís easy to become enamored with this opal.

Most of the opal from Wello is hydrophane opal. Hydrophane opal quickly absorbs water and the opalís base color appearance changes, becoming very clear. The play-of-color, though not entirely disappearing, fades out. But luckily this is only a temporary problemÖwhen the opal is allowed to air-dry for 3-4 days, almost like magic, the body color and play-of-color return to normal.

When cutting this material I use Elmerís Glue-All to glue the stone to a ºî x 5î long wooden dop stick. Let the stone dry overnight, then coat the non-waterproof glue with a coating of clear fingernail polish to make it waterproof. I use a 220-grit diamond grinding dry wheel to rough grind the stoneÖdry. Opalís relatively soft and a 220-grit diamond wheel cuts fast enough and also doesnít leave the deep scratches (and wonít be as likely to chip) that an 80 or 100-grit wheel willÖespecially when working dry. Watch for heat and dust (you might want to use a mask if youíre doing a lot of opal cuttingÖopal dust can cause silicosis), but with light pressure on a diamond wheel, opal doesnít heat much. But it is important to check you stones temperature often.

I like to do the rough grinding dry, allowing the stones play-of-color to stay bright, to properly orient and rough shape the stone. But once that is completed I go to my normal water-cooled method of opal cutting using a 320 grit belt, on an expanding drumÖfor final shaping of the stone. And 600-grit will remove any leftover flat spots and course scratchesÖthen onto 1200-grit and 3000-grit with a final polish using a mix of tin oxide and Linde A (10:1 ratio). If youíd like, a disk with 50,000-grit diamond will give you a super final polish.

Remove the fingernail polish coating by swirling in a jar with acetone in it for about 20 seconds (careful acetone is VERY flammable). Soak in a glass of water for 2-3 hours and the stone should fall off of the dop stick. If not let the stone soak overnight. Iíve never had a problem releasing the opal if it is allowed to soak in water overnight.

Keep in mind this is just one of many cutting techniques that will accomplish the same resultÖa beautiful, well cut opal cabochon. The important things to remember are: cut slowly, avoid over-heating your stones, smooth out flat areas and polish your opals wellÖchecking carefully for scratches.