Goldstone might not be a real stone, but it’s rich in character and history. It was once commonly called aventurine glass because it imitates that of aventurine feldspar, known as sunstone. This material dates back as far as the early 1700s, when it was first made by glassmakers in Venice, Italy.
How Blue Goldstone & Other Colors Are Made
The process of making goldstone is quite different from the process of making most types of decorative glass. First, the clear glass is heated. When it is molten, copper granules are added and allowed to melt. Once the cooling process starts, the copper forms crystals, which provide the glittery effect you see in the finished glass. The color comes from the added copper. Goldstone is primarily known for its orangish-brown color, but there are a couple of other variations. It can also be found in blue/purple and green. These different colors are obtained by adding different minerals to the molten glass – cobalt provides a blue color, and chromium provides a green color.
How to Purchase Goldstone
Finding goldstone is still rather easy; most online sales venues and shows usually have some available. Picking out the material is just as easy. It comes in chunks of broken slag glass ranging in size from one pound to approximately 10 pounds. What you see is what you will get by looking at the outside of each rough chunk. The great thing about working with material like this is that there is little to no waste. The color and pattern go through and through.
Best Techniques for Slabbing Sparkly Glass
When starting to slab this material, I would highly suggest not using an aggressive agate blade. Most lapidaries won’t have a glass blade handy, but using the thinnest continuous rim blade works best. Be cautious if you hand cut on a small trim saw, this material loves to chip small chards off the entire time. You don’t want to push your hands down the deck of the saw through broken glass particles.
You might also examine the rough chunk first. Even though there’s no right or wrong direction to cut, in my experience, the glittery effect seems to be greater on a certain plane. I believe that’s caused because of how the glass melted – the crystals most likely settled horizontally, giving that direction a far greater glittery look.
The gold-colored stone always seems to have continuous color, but I have noticed dark swirling bands in the blue and green variations. The dark bands aren’t really a structural issue; it’s just something you will have to work around when inking out your preforms on the slabs before trimming out your cabochon designs.
Cabbing Goldstone for a Mirror-Like Finish
Cabbing goldstone is rather simple. You can start on an 80-grit steel wheel, or even a 220-grit steel wheel, to shape and dome your cab. At this point, it will be quite hazy and riddled with scratches. This is to be expected with any glass or obsidian, including Mexican peanut obsidian.
At this point, move on to either a 140-grit soft resin wheel or a 280-grit wheel. This is where you want to smooth it all out and get all the major scratches out before moving to the next step. It’s important to thoroughly dry the cab off occasionally to check for scratches. They will stand out prominently as white lines. Once they are all gone, move on to the 600-grit soft wheel and start to polish the cab. Do not go any further if scratches appear.
Most glass and obsidian will still show micro swirls in the finish, which is okay; the polishing wheels will take care of those. Continue your way to the 1200-grit, and up to the 14k-grit wheel. This should yield a beautifully polished cab.
If at this point, you still have some dull spots in your finish, you can put on a final polish by using either cerium oxide on a leather buff or Zam polishing compound on a felt tip with a Dremel tool. Be sure not to overheat the stone too much, to avoid it fracturing. The result will leave you with a beautiful mirrored finish cabochon with tons of bling.
This What to Cut column about goldstone previously appeared in Rock & Gem magazine. Click here to subscribe. Story and pictures by Russ Kaniuth.
