THE PREMIER MARKETPLACE FOR REAL OPALS

Published at 5th Feb 2019

Modified at 4th Jan 2023

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.


21 people found this article helpful

Was this article helpful?

Share this article:

Search the Opal Encyclopedia

Related Articles

Australian Black Opal Information

Australian Black Opal is one of the rarest gemstones on earth. It has every color of the rainbow on a black ground which makes the colors dance.

8th May 2018

Boulder Opal Information

Boulder Opal is one of the most undervalue opals valuable on the market. Learn more about this unique opal and browse the beautifully stones we have for sale.

29th May 2019

Opals Make for colourful Business

With a passion for opals, Wayne and Estella Sedawie established Opal Plus more that 14 years ago and have found the internet to be a valuable tool. It’s where most of the company’s international transactions take place.

17th Oct 2018

Latest Articles

Opal Value: How Opals are Graded & Prices of Each Type

An opal’s price comes down to a variety of factors, all of which we’ve broken down in this guide to opal grading and prices. Learn all about opal grading and the prices of each type of opal!

19th Jul 2023

The Healing Power of Opal

Come on a journey and learn about the healing power of opals from our guest writer Vivien Schapera from Crystal Healing Techniques!

20th May 2023

The Flame Queen Opal: World's Most Expensive Opal

The Flame (or Fire) Queen opal is the world’s most expensive opal, sold for the modern equivalent of $3 million dollars. Learn all about its history and qualities!

18th Feb 2023

Article Categories

Opal Information

Information about Opal and its colorful history

103 Articles

Testimonials

Feedback from our VIP customers

5 Articles

News

What's trending in the Opal Industry

41 Articles

Technical Opal Information

All there is to know about Opals including Black Opals, Ethiopian Opals & Boulder Opal

15 Articles

Did you know?

Check out our fascinating information and articles on all things amazing in the Opal world

43 Articles

Opal Stories

Feel like reading a yarn or two?

6 Articles

How To's

All of your favourite Opal How To's

20 Articles

A-Z Of Opals

A complete list of your favourite Opal from all over the world

31 Articles

Opal Auctions Verified Sellers

Opal Auctions sellers who are approved as opal Verified Sellers

4 Articles