Cutting black opal

Cutting black opal DEFAULT

How To Cut Black Opal

how to cut black opal

This is a great guide for cutting Black Opal. This article contains thorough information from an expert opal cutter, who has a strong passion for black opals and has been in the trade for many years. He provides information on all the necessary equipment needed to cut black opal. See an inside perspective of cutting, shaping and finally, polishing. There is a special section on tips and tricks for cutting a black opal the best possible way. Black opal is considered to be the ‘Queen of Gems’. Historically, it is highly sought after by kings, queens, emperors, maharajahs and sultans. Its’ unique beauty is something to be marvelled. This guide is perfect for all levels. If you are a beginner black opal cutter, it has pictures for every step of the way, however If you have been cutting for a while, it can still be very helpful to refresh your opal cutting knowledge. We hope you enjoy this guide.

Equipment to cut Australian black opal

What You Need to Start Cutting Black Opal

  • Dop Sticks 
  • Trim Saw with thin blade (optional but very useful) 
  • Strong glue or Dop wax 
  • Diamond grinding wheels ranging from 80, 220, 600, 1200, and 3000-grits 
  • Blade (with rim thickness approximately. 0.02”) 
  • Polishing Disk 
  • Rough Leather 
  • Lamp (with 100-watt bulb) 
  • Tin Oxide Polish 
  • Dust mask, Old work clothes and Safety glasses
  • Water supply (Many cutters do not use enough water while cutting and polishing boulder opal )

Cutting a black opal nobby

Cutting a Black Opal Nobby With a Porcelain Top

This is a natural nobby from Lighting Ridge Australia. It has been rubbed down by an opal miner to expose the bright flashy blue opal color bar. The opal rub originally weighed 50cts and it cut to a beautiful 9.10 carat N1 black opal.

Rubbing down 50 carats rough black opal knobby on an opal cutting machine

The white porcelain top has to be rubbed down to expose the colour. White porcelain tops are rare and most of the time the opal will show bright electric blues.

Shaping the black opal on cutting wheel 600 grit

We have an old Gem master cutting machine that is around 20 years old and it just keeps going.

Cutting of the white potch

First Step - Rub Off The White Potch

With black nobbies it is important to find which side is up or down. Sometimes it can be very tricky if both the sides are black potch. If you purchase a parcel, always cut the lowest grade first and avoid cutting the rough with the most potential until you fully understand how the rough faces. If you only have one piece of rough, it is best to cut and work a small edge to see how the colour exposes itself.

Final polishing black opal on resin wheels

While rubbing down this nobby on a 400 grit diamond wheel you can see the color darkening inside this white potch. Using a 240 grit wheel is also fine for this stage. Just don’t press the opal too hard against the wheel or it could crack. Let the wheel work for you and always have plenty of water. Shape the opal on the 800 grit diamond wheel. Shape the stone by hand with a firm grip.

Dop the opal for cutting and polishing

Second Step - Dop The Opal

Place the opal on a dop stick so it is easier and more accurate to shape and polish. You can use a quick drying super glue to stick the opal on the dop stick and when you are finished cutting you can place the dop in the freezer for few minutes and stone will flick off easily.

finished polished and shaped  910 carats black opal

We have used green jewellers wax and a small methylated bunsen burner. Quickly heat the back of the stone so it is dry and then heat the wax and slowly drip or smear onto the opal. Than you just need your fingers to rub around edge to make a smooth finish. Many cutters burn their fingers doing this and it does take practice. Now with the dob stick you can control, shape the opal and start getting it ready for polishing.

shaping the black opal

Third Step - Final Shaping

On the last diamond cast wheel it is recommended to do some quick turns. This will ensure an even curved surface on the opal. A good way to see if there are any scratches is to hold the opal up to the light and roll backwards and forwards so the scratches are more visible. The polishing stage starts with a rubber polishing wheel that has 1200 grit and then 1800 grit. Keep plenty of water on the opal and twist opal frequently as they can heat up on these rubber wheels if pushed too hard.

polishing the black opal

Fourth Step - Final Polish

The final stage is to use a lapsa polishing powder. Pig leather can be used for this or the new gemshow lapidary polishing disk. Use a small amount of polish and be sure to remove all scratches.

black opal rough

tricks for cutting black opal

Tricks to learn when Cutting Black Opal

SEDA OPALS

Cutting challenge - this firey black opal rub had black potch in the face which was slowly rubbed off. I had expected to cut a pendant stone but the opal told me where to cut. The sand spot was deeper than I thought and at the edge of the stone the black potch started to appear and would grow bigger if i continued polishing. Instead of a pendant stone i got a stunning black opal ring stone with a lot of fire. It is such a pleasure to cut stones like this!! 

VIEW THREE ROUGH BLACK OPALS BEING CUT OPEN EXPOSING STUNNING OPALS

Black opal that has been mined at Lightning ridge is cut and polished in a similar style to all other opals. The most important aspect of black opal is to determine which side of the opal to cut. This may seem basic information but it is the most common mistake cutters make.

After purchasing a parcel of rough opal, never cut the most promising piece of rough opal. Always start on small pieces so you understand how the opal will cut. Start by rubbing a small corner of the piece to determine which side faces the best. Some grey rough will have a black centre so also rub on the grey pieces before you start on the black.

If you have large pieces of crystal opals they will sometimes cut better display colour if cut at an angle. There is alot of trial and error and no set rules with rubbing black opals. Except use common sense when cutting black opal. Cut small pieces and understand how the parcel will cut.

Even on the opal fields some opal mines will vary on composition on each layer as opal mined 20 feet down might be different to opal mined 40 ft down.

Another problem new cutters come across is that their new polishing wheels are too sharp and rub away the thin colour bars on black opals. I have seen an $800 parcel rough cut with sharp grinding wheels and only end up with a  $200 stone as the colour was rubbed away.

With new opal cutting equipment it is always best to rub a large rock or a piece of potch against new grinding wheels. Opal cutting equipment can be home made or you can purchase commercial opal cutting equipment.

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Sours: https://www.opalauctions.com/learn/how-tos/how-to-cut-black-opal

The opal fever has taken hold and there’s no holding you back now; your neck twitches and palms become sweaty as you say through gritted teeth “must… cut… OPAL!”

Well, my fevered friend, you’re in the right place. We’ve created many videos on Justin’s opal cutting process to help you learn how to work with the gem we love. Below you’ll find an extensive list on how to begin cutting opal.

Make sure you check out our YouTube channel where Justin cuts and polishes the gems we sell on our site. We’ve got a full playlist on learning to cut opalas well as learning about opal, mining for opal and more!

Watch a gem black opal emerge from rough

gem returned so I cut it and made thousands

One of our most popular videos ever and a sure way to catch opal fever! In this video, Justin cuts a piece of rough that was returned when a customer felt they needed a little more experience to tackle it. The gem that emerges is beyond what he expected.

What’s in my opal cutting workshop? A tour!

opal cutter's workshop tour

A good cutter never blames his tools… he makes sure he has good tools to begin with. Let’s see all of the tools Justin uses to make those brilliant cuts.

How to cut and polish an opal by hand

cutting opal by hand

A great way for beginners to try their hand at opal cutting (without investing in expensive machinery) is to do so by hand. Yes, it is possible! Buckle in, it’s a bit of a long ride.

What opal cutting wheel do I need?

Before you start practising your cutting skills, you need to make sure you’re set up right! In this episode, Justin chats about a question we get a lot from budding cutters; what wheel do I need?

How to change a lapidary wheel

How to change a lapidary wheel

If you have a lapidary machine and you need to change the wheel, we’ve created a quick tutorial on how to do so. In this video, Justin shows you the simple steps to changing your lapidary wheel with ease.

Maintaining a good polish on opal

Maintaining your polishing wheel

You can make or break an opal with the polish you give it, so how to do maintain a good polish on your opals? In this video, Justin shows you how to ensure you get a good polish every time.

How to carve opal

Justin uses a piece of rough that came back with us from a gem show in Tucson to teach you how you can carve an opal!

12 tips to cut and polish a better opal

12 tips to cut and polish better opals

Now that you’ve got the basics down, time to level up! Here are 12 tips that will help you to produce an even better cut.

Want to get back to opal basics?

Did you love this comprehensive opal cutting guide? Well, you’re going to love Opal 101: Everything you need to know!

If you want to learn more (or are looking to kill a few hours down a YouTube vortex) head over to our YouTube channel where Justin cut and polish the gems we sell on our site. We’ve got a full playlist on learning to cut opalas well as learning about opal, mining for opal and more!

Sours: https://blackopaldirect.com/opal-cutting-guide/
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Opal Cutting & Polishing

How to Cut and Polish Opal

FAQ:  How is opal cutting done? How do I cut rough opal? Where can I learn about cutting opals? How is opal polishing done? How can I polish an opal?

Opal cutting and polishing is a very specialised skill. Rough opal is normally purchased from the opal miners as ‘parcels’ (Bulk quantities of opal in its rough state). Potential buyers sort through the parcels and try to predict the value of stones which can be produced from the rough material.

However there is never any guarantee, as opal cutting can produce very unpredictable outcomes. Once the opal cutter has sorted through the parcel and decided which pieces are worth cutting, a diamond saw is used to cut the rough opal into ‘ rubs’ (opal in the rough shape of a stone). During this process, any excess material, cracks and potch (colourless opal) is cut off, and the piece of opal is cut into a basic stone shape.

opal cutting

Probably the most basic concept which any opal cutter needs is to keep the stone as large as possible, i.e. minimising waste and maximising the end size of the stone.

Each moment of cutting reduces the size of the stone, so control must be exercised.  The second basic concept is that opal can be ‘burned’ or may even crack if subjected to extreme temperatures. For this reason, water must always be used when cutting opal to avoid overheating due to friction.  ‘Burning’ a stone during polishing results in small pits forming on the surface thereby ruining the smooth surface and polish.

After the stone has been cut on the saw by hand, the opal cutter will then normally place the stones on ‘dop sticks’, consisting of nails or lengths of wood dowling, using heated wax to adhere the stone to the end of the stick. This allows a greater degree of control of the stone on the cutting wheel, especially when the stone is small. The wax is softened on a burner to permit the fixing of the stone, which is first adhered with the face of the stone pointing upwards. The face of the stone is decided by the opal cutter, considering which side has the best colour, and the best shape for the stone.

The opal cutter then uses a series of diamond grinding wheels (coarse to fine) to shape and perfect the stone. Importance is placed on removing imperfections, such as sand spots, and removing saw marks and rough spots from previous stages. The face of the stone is shaped into a cabochon (dome shape) and the shape is decided depending on the stone (normally oval). Again, maximising the size of the stone is an important consideration.

The final stage for the face is polishing. Serium Oxide is used as a polishing agent on a felt wheel with water to give the stone a beautiful polish. If the cutter is happy with the shape, and the absence of scratches, grinding marks or imperfections, he removes the stone and sticks it back on the wax with the back facing up.

The back of the stone is cut on the same set of grinding wheels, this time producing a flat bottom for the stone, and an edge which tapers up to the ‘girdle’. The shaping of the girdle is an important and difficult part of cutting, and refers to the point on the side of the stone where the two top & bottom edges meet. This edge is used by jewellers to set the stone underneath the gold, to provide a secure setting.

Boulder opal can be significantly more difficult to work. The opal forms in tiny cavities in the ironstone, therefore the seams of opal that run through the boulder can be of very excellent quality but are very thin veins from .25mm to 20 mm thick. The ironstone is generally left as backing to support the stone.

Occasionally a thick vein is deposited allowing the cutter to cut the opal in cabochon, however frequently the veins are thin and wavy, so the cutter is challenged to cut and polish the piece following the deposition of the opal, resulting in an undulating or baroque surface. Stones are generally cut into freeform shapes, which is dictated by the opal deposition and flaws within the piece.

Ironstone is also significantly harder than opal, (opal is only as hard as glass) which provides another challenge for the opal cutter. Opal will grind much quicker than ironstone, so extra care must be taken when polishing a surface comprised of both materials.

So, now you know how to cut opal! Well, not exactly… this is only a very rough guide, and it takes a lot of practice to cut opal correctly. We recommend that learners get hold of some cheaper rough material to begin with, and to get a feel for the stone. Cutting and polishing opal is a great skill, and it’s also very rewarding to uncover such beautiful colour!

Sources:

Sours: https://www.opalsdownunder.com.au/learn/opal-cutting-polishing/
The rough opal that taught me a costly lesson

The art of opal cutting

Opal Cutting

The cutting and fashioning of gemstones is an art. It is often forgotten that while there is an inherent beauty in the crystal nature of transparent gemstones, this is not always present in the opaque or translucent gemstones.

Non-transparent stones – even those of great beauty or value such as opal – are often mistakenly referred to as ornamental or semiprecious gems.

Opal is such a mysterious gemstone that often its beautiful play of colour is hidden. Only an experienced opal cutter can produce an exquisite gemstone.

So the opal cutter is an artisan of great importance, who alone can reveal an opal’s hidden beauty.

So how does an opal cutter begin? An examination of the rough is key, as the origin and variety of opal will often determine what a cutter does; in this way opal is like no other gemstone.

A cutter working on a Lightning Ridge (NSW) black opal will require a different skill to a cutter who is about to produce a gem from Queensland boulder opal, who again will treat the rough material differently to the cutter of a superb South Australian Andamooka or Coober Pedy crystal opal. Each variety possesses its own unique challenge for the cutter in terms of the thickness of the opal and the material that forms the back of the gem (ironstone for boulder, black potch for black opal, and so on).

Once the opal cutter has established the thickness of their opal they can assess what shape will produce the best gem from the rough and show the best “face”.

Generally, the cutter’s biggest focus is to create a full-faced gemstone of the most vibrant colour and to polish it to a mirror finish. Every opal is unique, so a cutter’s experience and intuition are important to success.

When it comes to boulder opal, the cutter must first assess how thin the opal veneer on the ironstone might be.

There’s often not much to work with here. Often less than a millimetre in thickness, the cutter won’t want to waste any precious opal. So they will interracially expose the layer of colour and follow it or trace it in an undulating nature to expose the vibrant colours. To allow this, boulder opal gems will often have an irregular surface and be cut in a free shape or free-form with irregular outline.

The opal cutter working with Lightning Ridge black opal, however, will often have the benefit of a thicker colour bar (as compared with boulder opal), so may choose to create a cabochon; cutting a high-domed precious gem if the colour bar agrees, or a lower-domed cabochon if that’s all that is available.

It is likely he will produce an oval-cut gemstone as this is generally the most commercially viable shape. But free-form and irregular shapes are also produced for exotic designer jewellery.

Crystal opal and Light opal may be used to create both standardised sized opal cabochons for jewellery and for more individually shaped free-form and opal carving. Much of the commercial grade opal jewellery with standardised, calibrated sizes is cut from Light and Crystal opal from the South Australian fields.

That’s not to say plenty of these stones aren’t still available for more exquisite shapes and carvings.

In considering the ‘face’ of the opal the cutter also takes into consideration the possibility of finding one of many named opal patterns – including ‘butterfly wing’, ‘Chinese writing’, ‘harlequin’ (often misused), ‘rolling flash’ and ‘flagstone’ among others.

Opal folklore is as vibrant as the stone; unique to Australia and to the outback regions of Australian pioneers from the 19th century.

As world renowned Australian opal expert Len Cram says, “Opal is like gold, once the fever is in your blood you can never get it out”. Any opal cutter knows how right he is.

Sours: https://www.gem.org.au/the-art-of-opal-cutting/

Black opal cutting

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Finished gem opals from our last LIVE jam cutting session

Just a coincidence, they are running around our yard with these laser pointers. We laughed, and he said that she and another group of guys managed to come to an agreement. They are all under the impression that their authorities have been decided, and then there are these, with a pointer. So they will be spectacled now.

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