What type of opal cutting machines can I use?
There are many cutting machines and ways to cut and polish opal. Finding the opal-cutting machine to suit you is the question that most people have on their mind when starting.
When choosing an opal-cutting machine, you have to take into account whether you are going to use diamond grits to cut and polish your opal or sandpaper, pumice powder, and cerium oxide.
If you decide to go all out using diamond grits to cut and polish your opal, you will only need three opal cutting machines.
Firstly you will need an opal cutting machine like a Pixie, or here in Australia, we have a machine called Gemmasta. These machines are wet and will hold all of the diamond wheels you will need to rough shape and polish your opal.
The most commonly used diamond grit wheels, in my opinion, are as follows.
Wheel1: 240 grit hard diamond wheel for roughing out your opal to the approximate size and shape of you want.
Wheel 2: 600 grit hard diamond wheel for the finer shaping on the dop stick to get the shape and dome you want the opal to have.
There are costly diamond wheels on the market called sintered wheels which have diamond impregnated 3 to 4mm into the opal cutting wheel. I use these wheels, and they have lasted my whole cutting career, so they are so worth the expense.
Wheel 3: A 1000 grit soft nova wheel for smoothening the opal and giving the opal it’s round smoother edges and dome.
Wheel 4: A soft 10,000 or 15,000 grit Nova wheel to give you a final polish,
The thing about diamond wheels is that you will probably have trouble getting an excellent polish. They have not perfected the polishing stages yet in a diamond.
My advice is to purchase flat lap felt wheel and use cerium oxide with water to brush the cerium oxide using a clean paintbrush to apply it onto the felt wheel, that way you will get the best polish possible. (Always re-applying to keep it wet)
The way I cut and polish opal is using hard diamond grits to start with, but then once I have finely cut the opal to the approximate size and shape, I change to a flat lap 1000 grit wet and dry sandpaper with cushioning as backing. (You must wear the sandpaper down with potch to get the right smoothness) This technique is an old fashion way, but still, I think the best and cheapest way to go.
Always using this part of the process dry. (A dust mask is handy to use)
Once I have sanded the stone, I use a felt wheel with pumice powder and water to get the pre-polish, final shaping and adjusting done.
Make sure you wash the opal and your hands well so you don’t get impurities in the final polish otherwise you will get scratches in your opal.
And then I polish with cerium oxide to finish the opal.
The back of the stone is smoothened out by re-gluing the opal upside down on the dop stick and smoothing the back to as fine a polish as you would like, sometimes giving you a double-sided polished opal.
Lastly, to become an excellent opal cutter, I think it is essential to own a slicer, to slab or split and take excess opal that is not needed away from the nobby.
A slicer also helps when the rough opal piece would be better cut into two stones.
Or there is more than one color bar in the piece.
Tip Number 1
I hope this has been useful to you.
If you have a piece of rough opal and you can’t see into it to see if the color-bar is clean.
An excellent tool for evaluating opal is to use a laser pointer. A laser pointer can assist you in peering into the depths of a rough opal piece. The beam when pointed into the color-bar will stop on any impurity, potch or opal that has no color. All you have to do is go into a dark room or shade (not sunlight) to see into the stone. This does not always work because some potch can be too black, but it does work most of the time. Once you have estimated where the impurities are in the opal, you can then start to figure out where the opal solid is to be cut out. With careful rubbing on a cutting wheel, you should have the first stage of the rubbing process done.
If you don’t have a laser pointer, you can use a bright light, but the light disperses a lot more, so it is harder to see into one particular area of the opal at a time. I have used a laser pointer for many years and has saved me thousands of dollars by showing up the inclusions that I would never have seen before with the naked eye. You can buy a laser pointer from any stationary shop or novelty shop.
Grey opal can turn black inside!
Often when I’m looking at rough opal, I can tell whether it will turn black inside. The telltale signs are in the natural breaks in the opal.
When you have a parcel of opal from the same area or patch, you can usually find small fragments (broken pieces) in it that will show you what body-tone it has inside the opal. Very often, rough opal can have a grey outer skin that makes the opal look lighter than it is. Inside the piece could be a different story. The potch can turn black and make the color-bar go dark as well; producing the opal black opal.
The benefit of doing this little test can be the difference between hundreds of dollars to thousands of dollars. Black opal is much more valuable than lighter opal and can reach prices of up to $15,000 per carat.