How to Grade Rough Opal ready for processing
To grade rough opal, you might just make three piles of stones. One pile represents the stones with the greatest potential with the most obvious color and of course, this is the main reason for checking the opal because if the stones are just black or white potch or ironstone, they are of little value.
The other piles might represent ‘B’ grade and ‘C’ grade and so on. Maybe you have five or six opal rough grades. At first, it might look like there isn’t any color at all and this is where a careful inspection is necessary because the opal is often hidden inside the stones.
How to Grade Rough Opal – boulder
Let’s begin at the top of Australia with boulder opal rough, which is found mainly in the Winton, Quilpie, Yowah, Koroit regions from north-west Queensland to south-west Queensland in the eastern States. This type of opal rough can come in large boulder iron-stones, or very small ‘nuts’ of ironstone with (hopefully) kernels of opal color. Having said that, you can crack open thousands of these kernels before finding any sign of opal so it’s a big risk trying to find color at times.
Indications of opal rough color
Even though it’s hard to find, there are certain indications that you look for. In the case of large boulder opal concretions, the miner, usually on an excavator, learns how to recognize the ‘level’ that he is working on. The ironstone boulders with opal potential are not difficult to identify once you have seen a few.
But the next problem is finding the color in the large rocks. The miner will chip away, usually at the bottom of the rock to look for color and if there are any signs of opal veins in the rock, he will break it again a long way from the color and just put the piece with the opal color aside for further inspection.
Most of us don’t drive bulldozers to find opal rough
So by the time we get to inspect the opal rough, it is in much smaller pieces. The miner has broken it down to the point that it can be handled and transported, and this in itself can be a challenge.
Often large 44-gallon drums are used on the back of heavy trailers to bring the material from 1500 km away to the coast where it can be broken down more with the aid of large diamond saws. Of course, many of the miners have this equipment at the mine site too, so they can avoid a long journey, carting a lot of valueless material.
So you have the rough opal boulder in front of you
What are you looking for that gives an indication whether or not it’s worth what the miner is asking? Well, you have to look for fine lines of color.
You carefully check to see if these lines or veins continue. Sometimes they can be seen on the other side of the rock and even if there is only colorless potch on the back end of the stone, it is an indication that the opal color is travelling inside the rock and it could be that there is at least a section of this vein with precious opal in it.
So you will attempt to slice out the piece where this vein most likely travels so that you can grind away at it and expose the color. So as you inspect the rough opal chunk, you have to look for these signs, and if there are enough of them, the parcel could be worth buying.
Buying rough opal is not for novices
It’s the easiest way of losing a heap on money as most of us through painful experience have learnt. Therefore, the best advice to give to folks who are buying on the internet is to look for parcels where the color has already been exposed by the cutter in Australia.
You see, a lot of us cutters don’t want to go to the trouble of completing all the opal stones that we find. We are a lazy lot. We would prefer sometimes to make a few dollars in between the miner and the hobbyist or professional cutter
and let someone else make the rest of the profit between opal rough and finished stones and by extension, jewelry. So take a look at the parcels at opalmine that have obvious color.
These parcels are called ‘rubs’ meaning that the rubbish has been rubbed off the rough opal, exposing the color.
This way you are not at risk of losing your money and you can still have the challenge and the pleasure of seeing the opal rough transformed into an amazing gem.
Buying rough opal from Lighting Ridge
Similar advice could be offered in purchasing this opal rough except that at Lightning Ridge you don’t have the problem of having to break the stone down from such large chunks. All the opal rough found here is in small nobbies, or seam pieces so you don’t have to hit it with a sledgehammer.
You can either take a piece of the end of it with a pair of snips, or slice it on the diamond wheel to check inside. But the same advice can be offered in regard to chasing color. Rough opal from Lightning Ridge usually doesn’t come in veins that swirl and bend throughout the stone.
The whole piece can be a chunk of opal, or you can get fairly straight ‘bars’ of color which can be more easily found if you grind around the edge of the opal rough.
Buying Lightning Ridge opal rough as Rubs
The same advice in regard to this applies to Ridge opal rough as it does to boulder opal rough. Try to buy parcels that have the color exposed so that there is not so much risk.
Buying opal rough from Coober Pedy, Andamooka, White Cliffs or Mintabie
Very similar advice to the Lightning Ridge information except that opal rough from these areas is nearly always seam opal and usually comes in lumps of opal which of course can be full of color, have a little color, or have very little or no color as in the case of potch.
Coober Pedy opal rough is easier to check and grade because generally, you can see the color after it has been washed and sorted. Usually, it’s not so necessary to buy it as opal rubs, but again, if you are on the other side of the world, it still makes sense to buy it in it’s upgraded form so that you are not paying big freight charges for a lot of waste material.
For examples of different rubbed opal rough parcels for sale, or rough opal advice take a look in the opalmine shop.