From Rough Opal Stone to Polished Opal Gem
This page features 5 videos that take you through the process of turning a rough opal stone into four high quality opal gemstones. The five videos cover cutting the rough opal stone, dopping the opal (the sensible and easy way), shaping the opal and the polishing of the finished opal gemstones.
1. Sawing The Rough Opal Stone
Before deciding how to cut your rough opal stone, first take the skin off the so you can get an idea of the location and quality of the colour bars. Once you have removed the skin, and inspect the opal, you will have a better idea on how many and what size the pieces of opal will be. You may even want to go as far as sketching some pencil lines on the rough opal stone to help guide you before making the final decision on how to cut the stone. In the video below, based on over 50 years experience, Peter quickly decides that to get the best value from this stone, he will cut it into four pieces.
When looking at the opal, hold it up to the light and inspect for cracks and imperfections such as sand as you will ideally want to remove these during the cutting stage. You obviously do not want a crack or a grain of sand spoiling and devaluing the finished opal gemstone.
The first rough opal stone in the video is a relatively thin stone, and this also influences Peter in his decision to cut multiple smaller gemstones. If you are cutting rough opal stones for commercial purposes, you also want to get as much yield as possible.
You will notice that Peter checks the opal stone under the light between each cut. This helps confirm or modify his initial thoughts on how and where to cut to get the best finished opal gemstones.
The second stone is thicker but only has a thin colour bar, so at first glance he feels that it would be most suitable for two stones that would form a matching pair rather than leaving it as one large stone. However before deciding on how to cut the stone, he first gives it a rough sand to remove the rubbish and get a better look at the colour bars.
The third stone contains low grade opal that will not produce gemstone quality opals but will cut into 10-15 smaller commercially saleable stones.
Once the saw has been used to cut the rough opal stone to the desired number of pieces, the cut stones are then roughly shaped on the course grinding wheel, then moving to the fine grinding wheel to get it close to the finished shape before dopping the opal for the final sanding.
During this process a decision is made which will be the top and the bottom of the finished gemstone, based on where the best colour bars are.
2. Dopping The Opal Ready For Shaping
Dopping the opal is a process of attaching the rough opal stone to a dopping stick using dopping wax. For this purpose Peter prefers to use three inch (75 mm) bullet headed nails of varying gauges. Although some use small wooden stocks, Peter prefers the nails as they are thin and always even allowing the greatest control of movement and spinning of the opal while sanding and polishing.
It is important to warm both the opals and the nails to maximum safe touch temperature. The wax should be melted but not liquid. A sticky paste consistency is best.
Place all your opal stones on the hotplate base up. Dip the tip of the nail into the hot dopping wax and then push it gently onto the back of the upturned opal stone. Check that the opal stone is firmly affixed and sitting perfectly square on the dopping stick. It is a good idea to wet your fingers before doing this as the wax will be at a temperature high enough to “hurt like hell” as Peter knows from experience.
On a cold day, you may find that the opal falls off the dopping stick occasionally as the adhesive properties of the wax is reduced. The day we filmed this, snow had settled on Peter’s car parked outside his garage. We also had the door open to get enough light to film the dopping process. During the filming of the sanding and polishing, the opals actually came off the sticks several times, but those sections were edited out.
3. Sanding and Shaping The Opal Stones
Once you have the opal stones firmly attached to the dopping sticks, you are now ready for the sanding and shaping of the opal. This is the most time consuming part and needs to be done using a gentle hand. Too much pressure and you could ruin a good opal gemstone. This is especially true if it is a high quality, valuable opal gemstone as you want to keep every carat possible.
The first stage is to remove the bumps and refine the basic shape of the opal. This is done on the fine grinding wheel. You will notice that Peter stops often to check the opal under the light.
Once Peter is happy with the shape, he moves on to the course sander. This process is a final shaping and removal of the grinding marks. It is vital that you keep the stone spinning and moving at all times so you don’t end up with flat spots that will ruin the opal and require you to go back to the grinder. Gentle gentle touch is the important word here.
Then on to the medium sander to remove the sanding marks left by the course sander. At this point you should not be needing to change the shape at all. The last chance you had to get it right was on the course sander. Here the words light and gentle are emphasised once more as it the constant movement.
Next is the fine sander. This is normally the most time consuming part and you need to get rid of all the fine sanding marks left by the medium sander. The more care you take with this final sand, the better the polish will be and the more beautiful the final opal gemstone will appear. You can push harder at this stage because on the find sander you are not going to grind the stone. However it is still important to keep moving.
Stop often and dry the stone before looking under the light. With a dry stone you should be getting a good reflection under the light while you are looking for any remaining scratches.
4. Polishing The Opal Gemstone
Polishing is done on a rotating disk, using a high quality leather pad on a rubber backing pad.
The polishing compound Peter uses is a Tin Oxide, mixed to a slurry with about 70% water and 30% methylated spirits.
There is no skill in this process. You can’t over polish the opal gemstone at this stage. No harm can be done unless you let the polishing compound dry out. You MUST keep it wet. Keep a spray bottle beside you at all times and constantly spray the polishing wheel to keep the compound and pad wet.
Once the polishing process is complete, you need to remove the polished opal gemstone from the dopping stick. A little tip Peter has for this is to put them in the freezer for a few minutes which hardens the wax and the polished opals can then more easily be removed.
5. Sanding The Back Of The Opal Ready For Setting
This is a relatively simple and short process but still an important part. You need to flatten the back of the finished opal gemstone and a small bezel ready for the goldsmith or silversmith to set into a ring or pendant. Due to the high quality of the four finished opal gemstones produced during the filming of this video, they will be set in gold and offered for sale as a matching set. Once the goldsmith has set them, I will add some photos of the finished opal gemstone jewellery.