Opal Cutting, Polishing, Buying, Appraising
Appraising Opal what to look at
When valuing an opal, there is many things to take into account. Type of Opal, Base colour, Location its from, Colourplay, Brightness, Clarity and more.
Other things to look at
As well as Type and Location, there are many other things needed to be taken into account. Play of Colour, Transparency, Clarity, Cut, Brightness, Weight, How much of a dome there is, Base Colour and others. These are the most important, and all will need to be used to give a clear overall appraisal of a stone. There are many other ways to llok at Opals, but they go into Gemmology/Crystallography and even Geology related to the stones being appraised.
Base Tone, Brightness,Hardness, Pattern
Above are some charts and information that will help evaluate an Opal. If its a Light Base tone, less value, if its a Dark/Black Base Tone, High Value. If there is a Rarer pattern added to the Dark base tone, more. The Hardness chart shows where Opal fits into the larger picture. The Brighness of an Opal is measured by holding the Opal up with a Natural Light source behind you, and seeing on a scale of 1-5 where the stone sits. If the Colour is popping in a darker room, or at a long distance from the viewer, it is often going to be a 5, where as Milky/Dull colours will be down at 0-1. The Pattern chartshows many, many different patterns, some rarer than others. There can be multiple patterns in one stone too depending on Base colour, and thickness of the colour bars exposed. One stone can shift from a pattern at one end, to a different pattern at the other. Generally a stone like that is worth less, than one with just a single Good pattern across the face. All these must be taken into account when apprasing an Opal.
Koroit/Matrix Opals
These are Cut and Polished Matrix/Koroit/Boulder (ironstone base) Opals. These are Small, have some pattern and veins, and slight Blue/Purple Fires. These are at the lower end of the value scale.
Koroit Opal Slab
As contrast, this Koroit Opal Slab, Polished Freeform, has Lots of Gem Veins/Patterns, many Nuts/Sections, Parts to it. Also has Thick Green/Blue and Purple Veins/Fires. As it is, a superb Museum type specimen, but if cut up and sliced/polished, would produce many cabs/Gems and be worth a lot of money. every stone is different, and requires its own seperate appraisal.
Cutting
This is a nice example of a Cutting machine. 6 wheels and a flat lap/polish pad on the end. An example of what these could be, 120-240-400 LHS Then 600-1200-10000 RHS and Final polish. All cutters have their own ways/stages and favourites. Getting this setup so it works is all part of the fun.
Dop Sticks
An important part of the cutting process is using dopsicks, certainly very important when the Opals being cut are Small. They are Sticks (clearly) which give you the ability to hold/move the opal much better than with just your hands. A wax/adhesive is used to stick the Shaped Opal to the stick, let the wax set, and then your away. This is usually done on the 600 Grit-polish section of the cut.
The Dremmel
The Dremmel is a hand held Tool like a drill that you can add a plethora of different attachments to, like grinding tools, polishing pads, and diamond saws. This is often used for Opals that have Curved bars, stange shapes to the Pattern/Fires or where the stone requires carving. There are many reasons for doing this, mostly to save precious Opal, where on the wheels it would be lost, and to make unique carvings that follow the Opal wherever it goes. Again that is saving Opal colour. The value of Freeforms/Dremmel cut stones varies widely, depending on all the other factors mentioned in the previous sections.
Buying Opal
When Buying Opal, the best way is in a Physical Shop, so you see what you are getting and hold the Stones in your hand. Talking to the shop owner is also a great way to find out information about the Opal. The example here is a Superb Underground Shop at Coober Pedy. Being in an undergound ex Mine will keep the temperature steady and is a prefct locality for a shop, and in Coober Pedy famously, houses and even a Church.
Opal Festivals and Gem Shows
Another great source of Opal, that has all the benefits of a Shop, are the Opal Festivals and Gem Shows. Above is a picture of the 2023 Coober Pedy Opal Festival. with all the vendors and a cafe. Great place to go meet the miners/cutters and see what is available. The Map shows the Australian festivals and locations. Each of these will have their own Unique sellers and Opal, along with the sellers that travel around to showcase the Opal they mined from all over Australia. Gem Shows are very different. They are usually large corporate events where sellers hire booths/stalls and go to showcase the Opal/Gems they have. The most famous show is in Tuscon Arizona, and also in Hong Kong (shown Below) but there are hundreds of Gem shows all over the world.
Online/Websites :)
Another way to buy Opal is from Trusted, Interesting and well stocked websites. Like the One shown here. The owner of such sites should be responsive to emails/Messages, have a good stock of Material with Pictures and honest descriptions, also Good/Fair prices to match. If you are not happy with the product you buy, there should be a no quibble/return and refund policy. Hopefully this information was useful and helps you on your Opal Journey...