![](https://df2sm3urulav.cloudfront.net/builds/24.36.6/assets/images/anonymous.png)
Published at 23rd May 2018
Modified at 4th Jan 2023
How To Cut A Slab Opal
Every now and then an opal miner will find such a massive
Opal that it takes some care and experience to cut it. This Opal weighs 200
carats (40 grams) and as you can see it is full of sand holes. There are also sections
of this Opal that need to be rubbed down to expose more Opal color.
First Step – Study The Opal
It takes years of practice and experience to be able to identify where the opal bars are going inside the stone. The first step is to always study the opal. Try and figure out where the opal colour bar is running and make an estimate of how far below the surface the colour is. This slab opal had no hidden bars and on the side it displayed black potch reaching the surface. It was decided the opal was best to cut with a saw first.
Second Step – Mark It Up
Once you have an idea on how you are going to cut the opal it is best to mark it out with a marker. This is going to make it easier when sawing the opal. This is especially true when talking about seam opal. Seam opal is opal formed in a long slab formation. An experienced cutter will check for colour bars that hidden or are undulating. The black lines are drawn on the surface showing the possibility for 6 clean Opals.
Third Step – Slab it Up
This is the fun part. Jump on the saw and slab it up. Follow your markings and you will instantly start to see what shape your opal is going to take.
When sawing always cut out the smaller opals first and then check that there is not an underlying bar of colour. Cut one stone at time and always double check . Do not cut out the largest opal first just in case the color bar dips.
Fourth Step – Rub it Down
This step is usually called ‘Rubbing Down’ or ‘Pre forming’. It is the rough stage of getting the Opal shape and is usually down just with the Opal in hand. Once you have rubbed a piece of rough opal it is termed as ‘a Rub’.
The opal we are looking at is a 200 carats rub from Lightning Ridge. The Opal Miner just slightly polished the top to show the potential colors in this rub. The specimen weighed 200 carats and was a big sizer (65 x 40 x 9 mm)
Fifth Step – Final Shape and Polish
The final step is to cut the opal on different grit wheel to get a nice polish on the surface. This is the stage where the opal is put onto a dop stick which helps with accuracy. The opal is shaped and polished to reveal the final opal.
The Finished Product
The large triangular opal cut is 23.25 carats and has two different patterns. It could have been cut into two opals but it is good to see a large black free form shape instead. This one opal would have paid for a parcel and the other 5 opals would be profit for the cutter. This opal is a text book example of a good return on buying a clean rub.
Interestingly that this opal rub was on Opal Auctions for years with over 3,000 views. No one was prepared to gamble on this piece. When cut the 6 opals weighed just under 40 carats so the cost per carat was only $56 per carat for finished polished Black Opals.
Buy Your Own opal Rough
Search the Opal Encyclopedia
Related Auctions
Related Articles
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 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
Latest Articles
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
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 (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
All there is to know about Opals including Black Opals, Ethiopian Opals & Boulder Opal
15 Articles
Check out our fascinating information and articles on all things amazing in the Opal world
43 Articles
Opal Auctions sellers who are approved as opal Verified Sellers
4 Articles