Stabilizing Ethiopian Opal
Ethiopian opal is beautiful, but it can also be troublesome to cut. Often it will fill with cracks or just crumble apart during the process, especially in the hands of those new to cutting them. Even if you’re experienced, however, you’ll find that there’s a lot of waste material that feels like it could have been saved.
Stabilization is one great route to ensure that your opals come out great, so let’s take a look into how to stabilize Ethiopian opal!
Should You Stabilize Your Ethiopian Opal?
Ethiopian opal is often hydrophane opal, which means that it has relatively large pores and “sucks in” water. While it’s a neat property, it also means that the opal is often less stable than we’d like.
Only rough material should undergo stabilization. There’s no real benefit to attempting this with a stone that’s already been cut.
This same open lattice will also allow for impregnation with other chemicals. In this case, it’s our epoxy and acetone mixture. Adding it to the stone will fill in these pores and keep water from getting in.
This material is known to be very touchy. I’ve had pieces of it that were nearly done crumble in my hands… when I was using diamond files and not power tools. The first few seconds on any belt or wheel are always kind of dicey when working with hydrophane opal.
This isn’t a normalized practice and should be disclosed. While some stones are stabilized as a matter of course (ie: turquoise, chrysocolla) it’s not done commonly with Ethiopian opal. A large part of that is simply that the material isn’t overly expensive at this point in time and there’s quite a bit of it on the market, it’s not uncommon for hobbyist cutters to cut stones over an inch in length… something which would stretch into a 5-to-6 figure stone when done with Australian opal.
My best advice would be to consider individual stones carefully by testing them for hydrophane properties. A stone being hydrophane isn’t a single level of porosity, it exists on a spectrum. You can check for the hydrophane properties easily enough: place your opal on a flat surface with a few drops of water and place the opal on it then observe the results.
The more hydrophane opal is the more water it will soak up. It’s easiest to observe this with a microscope if you have one since you need to be able to quickly distinguish between evaporation and the stone absorbing water.
Stones that are heavily hydrophane are the best candidates for this process. They’ll absorb the mixture more readily and they’re more prone to breaking in hand. In any case, make sure you disclose the material has been stabilized when it comes time to sell it.
How to Stabilize Ethiopian Opal
What You Need
You’ll only need a few things and about an hour in order to set up the stabilization process. Most important is our PPE:
- Safety Goggles- You’ll be using chemicals in a liquid form, so splashing is always a possibility. Wear safety goggles, or at least glasses to protect the front of your eye.
- Nitrile Gloves- We’re not just working with toxic chemicals, we’re working with sticky chemicals. Nitrile or latex gloves should be worn unless you feel like chipping off bits of epoxy from your fingers later that day.
- Respirator- You’ll need to either work outdoors or use a respirator. The fumes from acetone and epoxy are toxic.
For the actual process you just need the following:
- Acetone- At least 500mL should be used, but you can go down to 250mL if you don’t have a lot of material to deal with.
- 330 Epoxy- The usual fare works well here, but you can also try using other “ultra-clear” variations of epoxy. They’re quite similar overall. Standard epoxy syringes can treat about 1L of acetone.
- A Large Mason Jar- To hold our mixture.
- Stirring Stick- A wooden stirring stick is the best way to do this. Metal may be reactive and plastic has a tendency to dissolve in acetone. I use craft dowels I buy in big packages at Walmart for general workshop use.
- Big Mason Jar- For storing the solution during the process.
- Pyrex Dish or Baking Pan- Preferably one you don’t need anymore. Thrift stores are a good place to pick up either for a couple of dollars. You’ll be able to reuse it for this kind of thing but it won’t be suitable for cooking afterward.
- Diamond Files- For cleaning the matrix off material before stabilization.
That’s all you’ll need to get started, you can pick up everything at a hardware store in a single trip.
1. Clean and Prepare Your Opal
Now the “fun” begins. Cleaning Ethiopian opal is a bit more involved than just taking soap and water to it. In fact, we’re going to have to be careful about how we use either in order to preserve the material as much as possible.
Begin by grinding or filing off the matrix with as little water as possible. While it goes against my normal “wet work only” policy, I find the best way to do this is to put on a mask, go outdoors, and get to work. Flat files tend to work best, something in the 220 grit range is ideal if you have a choice.
You can also dip the file into a cup of water and use the file wet to keep down the dust. We don’t want to dip the opal in water if we can avoid it. Most Ethiopian opal has been dried for some time before it makes its way to you, usually a few months, and soaking it in water means you’ll have to let it dry out again.
A tiny bit of water won’t affect the process quite as much.
Afterward, you’ll need to remove the dust from the surface of the stones to make sure it’s as open as possible. I prefer to use a microfiber cloth like those used for cleaning glasses, they work very well for lifting fine dust from the surface of stones.
If you used water during this step make sure your stones didn’t change clarity during the process. If they did, you’ll need to allow them to dry. The best way to do this is to use some desiccant packets in an enclosed container, where it should only take a few days before you’re able to move on.
2. Prepare the Stabilizing Mixture
The stabilizing mixture is pretty simple in theory: you’ve got epoxy which hardens when the two compounds are mixed. Both are soluble in acetone, which will also move into the pores of the opals you’re looking to improve.
The stabilizing mixture is pretty easy to make and you don’t have to be overly precise while mixing it.
There are a few things to remember.
The first is to use your respirator if you’re making the mixture indoors. Both of these chemicals contain some nasty volatile compounds that are known carcinogens. Acute exposure to either will have minor effects, but prolonged exposure is a terrible risk.
The second is to make sure that you’ve got your glasses or goggles on. Splashes happen and you don’t want any of this in your eye.
In general, you’ll want to use roughly one standard syringe of two-part 330 epoxies for each liter of acetone that you’ve got in front of you. Most people use around 500mL, I’ve used even less when doing just a few small stones. So you’ll probably use about half of your epoxy tube.
Pour the acetone into your jar or bottle, then start putting in the epoxy. Do it slowly while stirring with a wooden stick. Make sure not to use metal or plastic for this, metals are reactive and plastic may melt in the acetone. Wood won’t react and you can dispose of it afterward.
Try not to get any of the mixtures on anything important when you’re done stirring, it will form into a hard epoxy in just a few moments as the acetone evaporates.
Now all you need to do is drop your opals in the mixture and close the jar. Failure to do so will result in a disaster as the acetone evaporates and leaves behind a hard resin that traps your opal.
3. Soak the Opal
The opal will need to remain in the jar for some time.
That I’m not sure of. My preferred method of timing stone stabilization is suddenly remembering I mixed a batch months ago at 2 AM and taking care of it in the morning.
As a general rule, you’ll want to go a bit longer than turquoise which is usually left in the solution for a month. You may want to allow for six to eight weeks in this case, especially if the hydrophilic properties of the opal were on the weaker side of things.
The extended period of soaking is to allow the epoxy to work deep into the opal, allowing you to cut it without fear of grinding out all of the epoxy immediately. The acetone/epoxy mixture will replace any water left in the stone over time, except for that at the molecular level, and create a consistent hardness through the stone when it dries.
So, at least a month and up to a year. 6-8 weeks should be good for the majority of Welo opal.
4. Allow It to Dry
Take your Pyrex or baking pan and set it out somewhere dry, then bring your jar over. You can use long tweezers or a gloved hand to pull the stones from the mixture.
Spread them out so they have a bit of room. There’s no point in laying down anything like newspaper or aluminum foil, these thin materials will just intermix and get attached to the stone when you pull them off.
Since your opals are uncut dust is less of a concern, but some will settle on the exposed surfaces of the opal. These will grind out easily, and even a quick hand polish will remove the worst of them once the stones are dry.
Allow the stones to dry over the course of about a week. If you remember, try to turn them once a day or so, which will keep the amount of epoxy between the dish and the stone smaller. In some cases, the stones may be stuck to the surface. Especially if you used a metallic baking pan.
In those cases, take a razor blade or very thin knife, dip it in acetone, and work it underneath. You want to “cut” through the epoxy instead of prying. Even with stabilization Ethiopian opal can break easily and prying the stone away from hardened epoxy is a great way to do it.
Using a razor blade also lowers your chance of accidentally flinging one of the opals into the back reaches of the workshop.
After a week the stones should be stabilized and ready to cut. Take the normal precautions when cutting them, opals are silica which is nastier than the hardened epoxy for your lungs. They may smell a bit differently.
If you hit a “wet” spot during cutting then you should let it dry out before continuing, but this is rarely a concern.
You can either keep your mixture or dispose of it. Unless something discolored my mixture, I generally keep it since you can use it on many different types of stone.
5. Disposing of Your Mixture
Disposing of this mixture can be a bit of a pain. If you pour it down the drain you’ll need to call a plumber, it’s toxic to plant and animal life, and you can’t just dump it on the driveway and let it evaporate since there’s epoxy in it.
Instead, contact your local landfill and ask them about the nearest HAZMAT disposal if you don’t have a place in mind already.
If you must dispose of the mixture at home then you should place it outside on a sunny day to allow the acetone to evaporate. The epoxy mixture will harden into a non-reactive resin at the bottom and this can be disposed of as soon as it’s dry and no longer smells of solvents.