(1)    Trim Saw:

150mm (6”) Lortone with the blade ‘just’ submerged in a well of water, fitted with:

–   0.014” / 0.36mm thick diamond blade.

 

(2)    Cabbing Machine:

150mm (6”) x 6 wheel Gemmasta ProCabber stainless steel cabbing machine, 1,775 RPM, fitted with:

–   ½ HP fully sealed motor.

–   Brass needle valve water taps.

–   180 grit diamond plated wheel 150mm x 38mm (6″ x 1.5″).

–   325 grit Sintered diamond wheel 150mm x 38mm (6″ x 1.5″).

–   600 grit Sintered diamond wheel 150mm x 38mm (6″ x 1.5″).

–   800 grit diamond FLEXMASTA wheel – dark blue.

–   1,800 grit FLEXMASTA wheel – light blue.

–   3,000 grit FLEXMASTA wheel – pink.

 

(3)    Final Polish Unit:

Gemmasta GSP-8 with disk, plus interchangeable:

–   8” x ½” Magnetic Leather Polish Disc.

–   8” x ½” Magnetic Felt Polish Disc (rabbit).

–   8” x ½” Magnetic Felt Polish Disc (wool).

–   I use white or pink cerium oxide for the final polish on my solid Opals from Coober Pedy and Lightning Ridge. I mix the powder with water until it reaches a milk-like consistency, then apply it to the felt wheel with a paintbrush while the machine is running.

–   Keep the polishing pad wet at all times, don’t let your Opal get hot or it will crack!

–   Keep the polishing discs in zip-lock bags when not using them, and keep the polishing unit covered at all times when you’re not using it, you don’t want dust contamination.

–   Clean (hose) the final polishing pad(s) if you ever notice scratches appear on your Opal, that weren’t there before you started the final polish.

 

(4)    For both carving and final polishing my Boulder Opal, I use:

–   ‘Dremel’ branded Drill (with flexible shaft attachment for grinding and carving).

–   ‘Dremel’ drill press (aka: “Dremel Rotary Workstation”), set to 90 degrees (horizontal).

–   An array of Sintered Diamond bits (or Burrs).

–   A couple of different shaped sets of ‘Nova’ burrs.

–   Many different shaped felt ‘bits’ or ‘burrs’.

–   Home-made diamond powder / coconut oil mix for the final polish on my Boulder Opal.

 

(5)    Dopping supplies:

–   Electric Dop station, for dopping large quantities of Opals in one go.

–   Methylated spirit burner with candle wick and cap on top, for quick Dopping.

–   Green Dop wax (a special wax mix purchased from Lapidary supply shops, in sticks).

–   Dop sticks – consisting of different sized wooden dowels & aluminium rod

–   I cut all of my Dop sticks about 10cm long.

 

(6)    Good Lighting. I use a mix of:

–   LED and Halogen Lights between 50w and 100w. (sometimes referred to as incandescent lights).

–   5600k (cool white / “daylight light”) LED light globes.

 

(7)    A Jeweler’s Headband / Loupe (or ‘Optivisor’) for cutting, and a small 10 x magnification Loupe for quality checks. These are underrated, but may be the most important tool that you will use while assessing each stage of the cutting process. Use these, and use them well.

 

(8)    Ancillary items:

–   Tweezers (for holding the Opal in the flame before dopping it).

–   Apron (to keep dry when cutting, as water generally flicks everywhere).

–   Tungsten Scribe (for scribing template shapes into your Opal).

–   Aluminium template set (for shapes you wish to cut).

–   Digital Caliper (aka: Vernia) (for measuring the size and shape of your Opal).

–   Digital scales, that can be calibrated, and can measure in carats. 1 carat = 1/5th of a Gram.

–   Safety glasses and earplugs.

The biggest mistake people make when starting out cutting Opal is trying to cut the largest possible stone from a single piece of rough. During the “studying the Opal” stage mentioned below, it is often far better to draw cutting lines through the rough and saw it into multiple smaller, more appealing stones, rather than aiming for one large stone. Cracks can reduce the value of an Opal to zero, so it’s always wise to cut along them where possible.

 

For my water supply to the diamond wheels, I use a gravity-fed watering system that I manually top up when needed. This prevents pressure surges from the mains water supply from damaging or blowing off the water lines, something I’ve experienced before.

 

Always keep a small bowl of water nearby, especially when dopping Opals. Dip your fingers into the water before touching or shaping the wax around the Opal to prevent the hot wax from burning your fingers.

 

The polishing unit should rotate so the wheels throw water and fine Opal particles downwards into the tray, never upwards towards your eyes. If this occurs, the motor either needs rewiring or rotating 180 degrees to reverse the direction of the main pulley belt.

 

Cut your Opals in a way that allows you to see the “gap” between the stone and the wheel. In other words, always look slightly over the Opal while cutting. This gives you greater control and allows you to better judge the developing shape.

 

Never press hard on any wheel, ever. Diamond wheels, especially “Nova” wheels, are designed so Opal grinds away easily with very light pressure. Although this approach may take slightly longer per stone, focusing on light pressure throughout every stage will produce a far superior finish. Your polish between wheel stages, including the final polish, will improve dramatically, and your wheels will also last much longer.

 

When cutting on any wheel, always use light pressure and continuously move the Opal across the face of the wheel from side to side, including circular motions where necessary. Developing the habit of “pressing lightly” and “using the entire wheel surface” will significantly extend the life of your wheels.

 

Never get frustrated, and never say to yourself, “She’ll be right.” If you begin feeling anxious or mentally fatigued, stop immediately and take a break. This is extremely common in Opal cutting, even for professionals with many years of experience. Intense concentration for long periods will eventually lead to fatigue and headaches.

Use this feeling as a reminder to step away briefly. I personally like to do arm and eye exercises. Yes, eye exercises are important. Go outside and focus on objects at varying distances, such as your hand, distant hills, or birds in trees, constantly changing your focal distance for several minutes. Some workplace OH&S procedures now encourage eye exercises for five minutes every hour. I do this regularly, even while writing this guide, and I’m fortunate enough that I still don’t need glasses.

 

When cutting any type of Opal, a constant water flow is essential for two main reasons.

Firstly, the Opal must remain wet at all times to prevent heat build-up. It doesn’t require a large amount of water, but if the stone becomes too hot, it may crack, “pop” small pieces from the gemstone, or even shatter completely.

Secondly, Opal dust contains crystalline silica, which can cause silicosis if inhaled. Silicosis is a serious lung disease that can contribute to COPD, an umbrella term covering conditions such as emphysema, chronic bronchitis, and chronic breathing difficulties. These diseases are irreversible.

When cleaning my workstation, especially when dry dust is present, I always wear an industrial dust mask and use ventilation or fans to minimise airborne dust exposure.

 

Another method for applying your “milky” cerium oxide mixture during the final polishing stage is to place it into a spray bottle, similar to those used by hairdressers, and spray it liberally onto the felt wheel until excess liquid begins flicking from the sides. Some people use far too much cerium oxide. As a general guide, approximately 3 teaspoons of cerium oxide to 500mL of water is sufficient.

 

For the final polish on Boulder Opals, many people stop at a 3,000-grit wheel, which I personally believe is simply cutting corners. These incredible Queensland Opals deserve a higher standard of finish.

After the 3,000-grit stage, I continue to a 20,000-grit diamond paste, followed by a 50,000-grit diamond paste. For my top gem-quality pieces only, I use a 100,000-grit diamond paste, and the results truly sparkle.

When the Opal has been prepared correctly throughout each cutting stage using light pressure, the final diamond paste stages often take only seconds. You’ll quickly learn when to stop polishing, as the glass-like shine appears very rapidly.

Personally, I prefer a true glass-finish polish on all Boulder Opals, compared to many in the industry who avoid spending extra time polishing ironstone-backed stones. I think that’s unfortunate, because the difference between a 3,000-grit finish and a 50,000-grit diamond polish is remarkable.

A common industry phrase is, “Are you doing a show polish on your Boulder?” But in my opinion, these Opals deserve it. Of course, each cutter has their own style and preferences.

 

If you’ve equipped yourself with the machinery listed above, followed the tips I’ve shared, and combined them with the detailed step-by-step “How to Cut and Polish Opal” guide below, you’ll be well on your way to producing truly brilliant Opals with a mirror-like finish.

I know I repeatedly emphasise the importance of pressing lightly on the wheels, but I’d like to leave you with the most important advice I can give: be patient, work carefully, and keep practising until the entire process becomes second nature.

When buying rough Opal, there are a few things you should ask, and also a few things to look for. Buying rough shouldn’t be hard, and generally isn’t, if you know what to ask for, and if the seller understands what you’re talking about, and what you want.

Anyone who sells rough Opal, or Opal from the field generally wants 2 things. The client to be happy, and a returning customer. That keeps the industry going!

Yes, buying rough can be risky, as you’ll probably get a heap of common potch mixed in with your parcel, but, it’s cheaper than ‘rubs’, and the chance that something nice might turn up, is sort of like playing the lotto, and the reason cutters love Opal. As it’s the excitement of unveiling that color that no-one else has ever seen, for the first time ever, that keeps you coming back for more.

The general terms you’ll hear from sellers are: “there’s a pretty good chance in there”, or “You’re definitely getting value for money”, or “You should definitely recover your costs of the whole parcel with just than one Opal”, and the list of lingo goes on and on.

When you’re starting out, ask for a relatively inexpensive parcel that contains mostly Opals that are easy to cut. You’ll generally get a parcel of light-Opal, or, semi-crystal Opal containing a lot of blues and purples. This is a great place to start.

It’s the same with Boulder Opal, ask the seller for relatively inexpensive parcel of rough with some potential, or, a parcel of ‘slabbed’ Opals with some color, that will be easy to cut. You may get boulder ‘split’ type material, but more commonly, you’ll get conglomerate. Conglomerate Opal is great, it contains many different patterns within one big stone, and you can generally saw out many nice ‘cutters’ from one big lump of rough.

When you know what to ask for, the seller will know exactly what you want. Always buy ‘low-grade’ material to start with, until you get comfortable cutting Opals, and then start to ask for a ‘step-up in color’, or, a ‘step-up in grade’, and this will get you into some nicer stuff.

When buying Lightning Ridge material, (from my experience), it’s always easier to obtain a parcel of seam Opal from out at the Grawin / Glengarry / Sheepyards areas, and easier to cut Opals out of these parcels when starting out. Mind you, there’s some very expensive and beautiful seam Opal out there too, so don’t think I’m saying seam Opal is cheap… I’m just saying that it’s easier to cut when starting out! Then when you’re ready for a bigger challenge, start getting into some Nobby material from the mining areas closer to Lightning Ridge, for example, the Coocoran field, or the ‘nobby fields’ as they’re generally referred to as.

As your technical cutting abilities improve, so will your Opal buying terminology.

Buying rough is fun, especially out at the fields, and most sellers will let you return a parcel (within a short time frame) if you’re not satisfied with it. This is only if you haven’t sawn it, cut it, or started to grind it down in any way! For obvious reasons, this would be extremely immoral. The Opal industry is very small, so don’t ever try and rip anyone off, or do anything unconscionable, or you simply won’t last long, and you’ll need to find a new career, if that’s your intention.

When you’ve got an Opal in your hand, the most obvious thing to look for is color. From there you want to find the ‘seam’ or ‘flat line’ of Opal color that exists within the gemstone, finally, you want to decide which side is the ‘top’. Make sure that you’re using a good Halogen light source, or are in the sun when studying your Opals, as you need to see the color properly. A good thing to do is keep the Opal wet, as this helps bring the colors within.

To do this, imagine a piece of cheese with sauce on one side of it, stuck between two buns. You want to spend a lot of time looking at the bun from all angles, to decide whether the slice of cheese (or color bar) is brighter on the side with sauce, or the side without. Now that you’ve made your decision, (keeping that analogy in mind), you want to take the bun off one side only. In other words, you want to grind the ‘host stone’ down to land near the color bar that is brightest, exposing the brightest side of the color bar to your eyes, whilst at the same time, leaving a nice potch base underneath the color bar for support. Sometimes one side of an Opal gemstone is naturally darker, or even has a black potch backing, in that case, you’ll always want to remove the ‘whiter’ side of the Opal. As it will generally be brighter with a darker backing.

Always remember to put on some old clothes, especially if you’re going to cut Boulder Opal. Also put on your apron. (When cutting, I like to lay a towel over my legs as well).

Before deciding which is the ‘top’ of the gemstone. It is best to grind away the sides of the Opal, following the color bar around the Opal. In the analogy above, you’d be grinding around the sides of the bun to expose the cheese, so that you can see it from all sides, when you turn it around 360 degrees. When doing this, you don’t have to worry about shaping your opal, as you’re just assessing which side is to be faced. So don’t grind away too much opal chasing the seam around the gemstone.

Once this is done, and you’ve studied the Opal and decided on which side the top of the Opal is, it is generally a good idea to mark the top of the Opal with a permanent marker. (Since you spent all of this time studying it, and may lay it down to ‘face’ another day). When taking the top of the Opal off, to expose the color bar, the term for commonly used within the Opal industry is, “Facing the Opal”.

Sometimes it is easier to ‘saw’ the host stone (or Potch) off with your trim saw, just above the color bar, so that you don’t have to spend too much time grinding the potch away to expose the color. Thus saving your wheels from wearing unnecessarily. Other times it just easier to use a rough wheel and quickly grind the potch off, if the Opal is small, or there’s not much host stone to take away. I like to use my 180 grit or 360 grit to quickly remove the host stone toward the color bar. Remember to always stop just above the color bar, as the rough wheels will take away color in the blink of an eye. Also remember to always press extremely lightly, as you can chip the Opal on these wheels and also make deep scratches.

Look for a layer of Opal within the ironstone host rock that is flat. The flatter the color bar, the easier it will be to shape the Opal. If the color bar is ‘wavy’, then you’ll generally need your ‘Dremel’ tool to grind down, or ‘carve’ the host stone away to expose the wavy color bar, or, if you wish to chase the color bar on your wheels, then imagine you’re looking at a tennis ball. You want to chase the color in the same way, so that it curves out toward you. The same principals of cutting (as mentioned above) applies to boulder Opal, with chasing the color bar around the Opal, looking for the brighter ‘face’ of the color bar, and also sawing away the host stone with the trim saw, to save wearing down your wheels. This is especially important for boulder Opal, as the ironstone attached to the color bar is much harder than common potch, and will wear away your wheels much quicker. Again, always press lightly and take your time when grinding! When exposing the color within Boulder Opal with a grinding wheel, use lots of water, and continually take the Opal away and dip it into fresh water and wipe the face off with your hand, or with a cloth, as the dark ‘muddy’ water that covers the Opal can often hide the color bar, and you may be grinding it all away. If you ever notice a thin layer of black potch between the color bar and the ironstone, then leave this in and cut the Opal so that the black potch stays underneath the color bar. This is referred to as a ‘Black Boulder’. The colour may come out quite brilliantly, like a black Opal from Lightning Ridge, or, even brighter! When you’re grinding away Boulder ironstone and come in contact with potch, or precious Opal, there will be a distinct difference in sound. Keep mindful of this, as it’s a clue as when you should be stopping more often to examine the Opal.

Once that you’ve ‘faced’ your Opal. It’s now time to start shaping your Opal. I use the 360 grit sintered wheel to start to get a pleasing shape, but I don’t spend too long on this wheel, I quickly change over to the 600 grit sintered wheel to finish facing the Opal, exposing as much of the color bar I can, without removing too much Opal, and finish shaping the top of the gemstone into a nice cabochon.

The shape you finish with on the 600 grit sintered wheel, will be close to the final shape of the Opal.

For the shape you choose, the Opal may ‘speak to you’, keeping it a ‘freeform’. Or, you may choose to use a template, and a tungsten scribe (or texta) to draw the shape on the face of your Opal. Depending on the type of Opal, and how I’m feeling, I use both methods to ‘scribe’ the shape. Sometimes I even color in the whole face of the Opal in, with a permanent marker, so I know “what to keep”, and I can track the process of my cutting easier. I’ve heard of people drying their Opals, and coloring the face of the dry Opal, before each polishing stage, to know when it’s time to grab the Loupe and have a look at the process. This has always appealed to me, and could save much time during each wheel. But, I’ve honestly never tried it, because I’d have to dry the Opal each time.

Before going onto the next stage of Dopping the Opal, you need to slightly ‘flatten’ the back of the Opal, ready for wax. You can go back to the 360 grit wheel, as I do, or just stay on the 600 grit wheel. Flatten, or ‘Cab’ the back of the Opal a little bit so that there’s a nice surface for the wax to stick to when you Dop your Opal. You don’t have to do this perfectly, as you’ll generally finish the back of the Opal last. I personally like to get the back of the Opal near perfect at this stage, so that it is much easier to finish the Opal within the final step. This way, there’s less time spent on the back of the Opal after your final polish, and therefore, less chance of a rough wheel accidentally touching the final polished face of the Opal, which has happened to me before..

Once you’ve pre-shaped the Opal by hand, all the way up to the 600 grit sintered wheel, and flattened the back (and remembering to try and remove any sand). It is now time to ‘Dop’ your Opal, ready for the final stages of “Cutting and Polishing”.

Always remember that wax won’t stick to a cold stone! You can Dop your Opal in one of two ways.

(1) Using a Dop Station, where the machine automatically maintains the wax to a specific temperature, generally set by adjusting the potentiometer on the unit itself. You can place the clean and dried Opal onto the hot plate (bottom side of the Opal down, no longer than 20 to 40 seconds) to warm up whilst attaching a small blob of wax onto the end of your Dop stick, and pre-shaping it to a tear drop. Then, with a set of tweezers, pick up the Opal and place it onto the hot wax. This method is great when you’re dopping up a huge batch of opals.

(2) Using a Spirit Burner, hold the Dop stick in one hand, while holding the clean dry Opal in a set of tweezers in the other. Spin the wax in the flame (but do not let it drip, if it does, you’ve got the wax way too hot) Switch between waving the Opal a couple of times in the flame, and then waving the wax through the flame, a few times more than you would the Opal! Place the Opal onto the wax.

Once the Opal is on top of the wax, you want to quickly dip your fingers into some water and start to adjust the Opal perfectly, before the wax sets. Making sure that the whole back of the Opal is evenly covered by wax, and also making sure that the Opal is not touching the Dop stick through the wax. When that seems right, spin the Dop stick between your fingers, left and right, as you want to see that the Opal’s color bar is perfectly horizontal to you. This will make the next stages of shaping the Opal on the wheels a much easier task.

As I mentioned above in my list of machinery and tools I use. I have a few different types of Dop sticks. I find that the most important part of using your Dop sticks to cut Opals, is consistency. Pick the sticks you like, but stick to the same length, and try to stick to similar thicknesses. I know that this will change with the different sized Opals you are Dopping, but, keep them all similar. The ‘feel’ you get with the repetition of cutting will help to give you a consistent, and more brilliant finish.

Remember to never let wax protrude, or exceed the outside limits of the Opal you are Dopping. You shouldn’t be able to see wax when viewing the stone from above.

TIPS: Always remember to keep your cutting machine clean, especially when frequently cutting Boulder Opal. The main reason is contamination. You don’t want dust, or different grits of diamond and opal stuck to any wheels, especially as the grit or grade becomes finer. This is especially important if your water supply to each wheel is from a recirculation system. I personally do not like these systems, but, if you’re using one, make sure that you attach a good filter to maintain flow on the suction side of the pump, and also try to use muslin cloth or something similar, on the outlets of each water jet. You really have to maintain the cleanliness of a recycled water system to totally eliminate the chance of contamination, to keep your Opals free from scratches as you go to finer grits when polishing.

Some people prefer to cut their Opals in batches. Using the harsher grade wheels to pre-cut and pre-shape everything before polishing their Dopped Opals, and then they fully clean their machines before starting this process. I think that this is a great idea, as there is nothing worse than scratches that keep appearing on your Opals from contamination, and nothing worse than having to go back and unnecessarily waste time to take scratches out.

Always press gently, and use extremely light pressure when polishing your Opal.

Regularly inspect your Opal with your 10 x magnification Jeweler’s Loupe, and if you notice that there is a sand spot that goes too deep to remove, or an inclusion that cannot be removed, or a dull patch of potch that may have to stay in the face of the Opal, as if it is ‘chased’, you may lose most of your color, then, it’s your decision to keep these within the gemstone, or, cut the stone into smaller pieces to try and remove them. Inclusions do reduce the value of an Opal, but, they are acceptable. These choices will continually arise when cutting Opal. This will constantly remind you how rare a beautifully finished, and inclusion free Australian Opal truly is. This is all part of the fun (and frustration) of cutting Australian Opal.

600 grit Sintered: Taking your Dopped Opal, always look over the Opal, and have the ‘face’ of the Opal facing you while you chase your shape template, or get to your desired shape by ‘eye’. Take your time in getting the exact desired shape of your Opal, and press gently. Continually turn the Opal around and around, never leave the Opal in the same place for too long, as this will create a facet within the Opal, and this is the last thing you want.

Once the outside shape is pleasing, now it’s time to get the dome you desire. If the Opal color bar is very thin, and you cannot create a dome, simply round / curve the edges of the gemstone into a C shape, and continue smoothly onto the face of the Opal. This will create the effect that there is a dome.

Remember to always keep the Opal moving to remove the scratches created by the harsher grit in the previous step, and always keep the Opal moving to avoid created new facets and deep scratches.

To create a dome, you can cut a 10 to 20 degree curvature across the top of the dome, then, on the outside edge, perform an angle cut at about 45 degrees, and then another at about 70 degrees. From there, you can gently take away the ‘sharp’ edges left from your angle cuts by blending them into one. Using circular and sweeping motions, blend all angles into one nice curvature, all the way around the Opal.

At the end of any stage of cutting on any wheel, this part will take practice, but, will give you excellent results on your Opal. By holding you Dop stick extremely gently, rapidly spin the Opal, and with the lightest of touch, gently press it against the wheel, making sure that you use this technique, touching the entirety of the Opal, on the wheel. This method will remove all facets and smooth the Opal.

To know when you’re finished pre-shaping. You firstly have to wipe the Opal dry, and check the entire gemstone, especially the face, with a Jeweler’s Loupe. Preferably a 10 x magnification Loupe. So that you can especially see the ‘consistency’ of the finish, within each polishing stage. There will be scratches, but, they should all be uniform, and a consistent thickness related to the ‘grit’ you are working with at the time. If there are abnormal or larger scratches or facets, then keep going on this stage until you are satisfied.

600, 1200 and 3000 grit ‘Nova’ wheel polishing:

I find that I spend most of my time making sure that the final shape is perfect on the 600 grit ‘Nova’ wheel, followed by probably more time spent making sure all scratches are removed on the 1,200 grit ‘Nova’ wheel.

The following applies to all 3 wheels.

Always keep your Opal moving, left to right across the face of the wheel (to wear the wheel evenly), and keep the Opal spinning around and around. Remember that you are totally removing the scratches from the previous wheel, or previous ‘stage’ of cutting, making the Opal more pleasing to the eye through every stage. Remember the sides of the Opal through each stage, and also focus on the face of the Opal. Most importantly, remember to always press lightly, this is extremely important when using ‘Nova’ / soft wheels. Again, wipe the Opal and check your progress with a Jeweler’s Loupe. Move on to the next wheel only when you are 100% satisfied.

If you’re ever feeling anxious, or tired, and feel you’re rushing any stage of the cutting process. Place your Opal aside, turn everything off and go and take a break.

Opals formed over millions of years beneath the earth, and they truly deserve 100% attention when cutting, as you’ll never find that Opal ever again. They’re as rare and unique as your finger print.

Final Polish on ‘Lightning Ridge’ or ‘Coober Pedy’ / ‘Mintabie’ Solid Opals:

Paint the ‘milky’ textured Cerium Oxide / water mixture onto your spinning hard felt pad with a paint brush, or, via a spray bottle, until you see the solution spitting off the side of the wheel. Take your Dopped opal and GENTLY touch it against the felt pad. Remember to ALWAYS keep your Opal moving around and spinning, and ALWAYS keep the pad wet.

I find that if you’ve done a great job on the previous cutting stages, then the Final Polish stage is the easiest of the lot. You have to constantly spin the Opal by rotating the Dop stick between your fingers. Making sure that you keep changing the angles of your Opal so that you get the sides, and turning the Opal upwards, or downwards, until you eventually end up with the top, or face of the Opal touching the felt pad. Continue to do this a few times, at all angles, and then wipe the Cerium Oxide off the Opal, or, dip it into a glass of very clean water to check the progress of your Final Polish. Do this by using your 10 x Jeweler’s Loupe until there are no visible scratches left on the Opal.

If your Opal gets too hot, or has a weird facet or a sharp edge near the back of the Opal, it can easily grip to the felt pad, and go flying out of your hands quite easily. It is common for an Opal to ‘fly off the dop” if you’re pressing too hard, or the Opal gets too hot and starts to grip to the felt. Keep full control of your Opal during the final polish stage, and keep that felt wheel wet. It is also common that scratches will start to appear if your Opal gets too hot. So, if you’re noticing new scratches appearing, keep up more Cerium / water on the pad, or move the Opal around more, or apply less pressure, and polish more gently.

The finish that Cerium Oxide produces is somewhere between 14,000 & 50,000 grit, depending on grade and quality of Cerium that you purchase. I choose ‘Optical Grade’, which is generally at the finer end of that scale.

 

Final Polish on QLD Boulder Opal:

Either (a) Use a felt backed Leather Pad, and paint or spray your Tin Oxide mixture onto the spinning Leather Pad. Gently touch your Opal to the pad, whilst utilising the same method mentioned above, making sure you keep your Opal constantly moving. Opal can easily ‘grab’ on the Leather Pad, so pay close attention to this polishing stage, and keep applying the Tin Oxide solution so that the Opal doesn’t get too hot. The Tin Oxide mixture that people generally use within the Opal Industry is 80% water and 20% methylated spirits, then mix enough Tin Oxide in to make a ‘Milky’ or ‘Light Gravy’ consistency mixture.

(b) Using your ‘Dremel’ tool, attach your 25,000 grit felt bit, (NB: that there isn’t such a thing as a 25,000 grit felt bit, it’s simply the bit you use, ONLY when polishing with the 25,000 grit diamond paste). Switch the ‘Dremel’ on and adjust the speed to somewhere between 10,000 and 15,000 RPM. Take a dab of 25,000 grit diamond paste, and spear it onto your Opal. Gently touch the pad against the opal, and start from the outside of the Opal, and work inwards polishing the Opal. This way, you’ll end up with most of your polishing compound in the centre of your Opal. Re-smear the polishing paste around the Opal and start that step again, moving toward the centre of the Opal. You’ll only need to do this a couple of times, and then you can start spinning the Opal around and keep it moving until you’re satisfied that the 25,000 grit finish is consistent.

Remove the 25,000 grit felt bit, and place in a clearly labelled zip lock bag so that it cannot get contaminated. Clean your opal in soapy water, or a sugar soap solution, and take out your 50,000 grit felt bit and attach it to the ‘Dremel’. Again, using the same method above, use your 50,000 grit polishing paste to complete the final polish on your Boulder Opal. Remember to remove and store your final polish felt bits in clearly labelled bags, free from contamination.

The secret in polishing Boulder Opal is to gently introduce heat into the Opal, a little, and your final polish will be much more noticeable, too much heat, and the Opal will burn. This takes much practice, but the end result is worth it.

There are a few methods for removing the Opal from the Dop stick. My preference is from top down:

–          Use a knife, and gently pry the opal from the wax, cutting between the Opal and wax

–          Place the Dopped Opal into the freezer for a couple of minutes

–          Place the opal in hot water (not boiling) for 2 minutes, and then remove the Opal

–          Gently heat the wax and Opal up in the spirit burner, and pry off

Once you’ve finished the Final Polish on your Opal, and it’s removed from the Dop stick. There are 2 ways to finish the back of your Opal. (1) – Dop the face of your Opal to the Dop stick, or (2) Finish the back of the Opal free-hand, by holding it in your fingers. I use method 2.

For finishing the back of Boulder Opals, I use the 360 grit Sintered wheel, and make sure that when looking at the side of the Opal, the distance from the top of the Opal, to the flat back, is parallel. I then get the Opal, and turn it 45 degrees, and cut a “Jeweler’s Edge” around the outside edge of the base of the Opal.

For my ‘Lightning Ridge’ or ‘Coober Pedy’ / “Mintabie’ Opals, I use the 600 grit Sintered Diamond Wheel to finish the backs of the Opals. I start by making the back of the stone parallel to the top of the stone. I then make sure that there is a very slight curve, or ‘cab’ in the back of the stone. Finally, I turn the Opal 45 degrees, and cut a “Jeweler’s Edge” around the outside edge of the base of the Opal. Making sure that the distance from the top of the stone, to this bevelled setting edge, is the same thickness, all the way around.

I finish the backs of my stones to 600 grit. Some people go to 1,200 or even 3,000 grit. But I personally think that this is a waste of time, as it’s only wearing out your higher grade wheels unnecessarily. You generally never see the back of an Opal gemstones, when it has been set into a pendant, or ring. The only exception to my 600 grit finish, is with a Crystal, or Semi-Crystal Opal, where I will re-Dop the Opal, and completely finish polishing the back of the Opal, to the same standard as the top. The color that shows through on the back, deserves this attention, as a Jeweler can set an Opal to display both sides.