Opals are known as the Queen of gems. Their sparkle, play of light, and color are mesmerizing and alluring in jewelry. Metal Clay artists were told Natural Opals cannot be fired in place in Metal Clay, and they need to be set in the traditional way with a bezel or prongs for inclusion in their Silver Metal Clay Jewelry. This was until we discovered a Cultured Opal that can fire to 1650ºF (900ºC).
Wow, the possibilities for artists working with Metal Clay and Opals have just busted wide open. Our minds went wild, and immediately we wanted our hands on them. Before we decided to offer them to the Metal Clay community, we needed to see for ourselves the heat tolerances of the stone, what you could do, and what you can't do.
We labeled this article Part I because we will be doing more testing on what other clays and kiln conditions are compatible. Meanwhile, Holly performed several intense tests to determine how the Cultured Opals work with Silver Metal Clay. You'll find the results of those tests below.
What We Found Out
This Cultured Opal material is a fascinating top quality Opal that takes 14 to 18 months to grow by experts in a lab. The colors are natural with no treatment or enhancements. Here are the properties that make this Opal so darn appealing, but do be aware, that not all Cultured Opals are alike, and not all have the same properties:
This Cultured Opal can be Fired for 30 minutes at 1650º F (900º C) in a kiln with Fine Silver. Tests were performed with an azure - a hole behind the stone.
This Cultured Opal can be Fired directly in a Torch.
Natural Opals are 5 - 6.5 on the Mohs scale. This Cultured Opal is 6- 7, making it more durable.
It has the same chemical composition as natural Opal without the water content.
Cultured Opals are sustainable in that they are NOT mined with forced labor and are renewable without being mined out of existence.
This Cultured Opal does not decompose or release substances or gases when heated to very high temperatures.
Tumbling in Steel Shot is not recommended, but some report success. We personally advise against it.
Buying Opals
Buying Opals can be confusing. What difference is there between Natural Opal, Imitation Opal, Fake Opal, Cultured Opal, Lab-Grown, and Synthetic Opal? What????
Natural Opals come from the earth. The Opal patterns are random and have not been enhanced in any way by humans other than to cut and shape them for jewelry.
Cultured Opal, Lab-Grown, and Synthetic Opal
This category of Opals and their titles are essentially interchangeable. The Gemological Institute Of America (GIA) has certified that Cultured Opal, Lab Grown, and Synthetic Opal have essentially the same chemical, physical, and optical properties, but are grown by experts in a laboratory.
Imitations and Fake Opals
These are look-like Opals, but they differ from the natural Opal's chemical makeup. Most imitation opals are made from glass, resin, or plastic.
Why Christopher Chose Cultured Opal
Christopher has chosen to work with Cultured Opals because they are sustainable having no environmental impact, and there is no forced and slave labor to obtain them. This is not to say all Opals mined are worked under these conditions, but there is an ugly underbelly in the Opal trade industry that needs intervention. Therefore, buying from a reputable dealer is encouraged.
Christopher now handles two types of GIA-certified Cultured Opal to date. His Artisan Cut Opals have a random matrix with attractive veining in many, and a variety of flash and color.
These Opals CAN NOT be fired in a torch or kiln. He also has Opal shards great for inlay projects and jewelry. Both of these are offered during his Friday Auctions on his Facebook page. He has chosen to sell them there due to the time it takes to cut them and not being able to keep them in stock on the Healing Phoenix Lapidary Website.
NOW, you will find the NEW Faceted Opals, both Round, and Rose Cut Opals, as well as Small Regular-Shaped Cabochons on his website, and these CAN be fired in place. They are a fine cut and calibrated in size. The difference in appearance is the pattern is more uniform throughout, and there is no veining pattern. Their shimmer, flash, and cut are what make them brilliant with lots of fire and appear different at various angles. Rest assured, Christopher is clearly describing them as Fire-In-Place or Non-Fireable in the descriptions, so you will know the difference.
Testing Day 1: Cultured Opal Testing the Unknown
Holly's first test was to see if the "Black Fire" Lab-Grown Opals could withstand 1650º F and be fired in place with silver. The gem below is only 4 mm because testing can get expensive fast, but man, it has a lot of fire. Do you see the red, orange, yellow and green? Holly tested other colors all week. She was excited to see if it would fire well, and she was inspired.
Testing Day 2: The Gem Survived!
Holly was trying to catch that amazing green flash of the "Black Fire" Faceted Cultured Opal. It has a deep rich red with flashes of red-orange fire and green fluorescence emerging from the highlights. The continuous play of color is mesmerizing, but hard to catch on camera. In the still photo, she was able to do it. They are tricky buggers to photograph! "Black Fire" Faceted Cultured Opal was tested first on an open kiln self at 1650 F for 2 hrs.
The second test was fired for 2 hours at 1650º F with 960 Enriched Sterling Metal Clay. This clay variety must have the entire 2 hours. The Opal gem came out with a slight haze on it, which Holly polished off with diamond paste and a mini buffing wheel with little effort.
She thinks she cleaned it well before firing, but she just "had" to go back and sand a little something again. "I couldn't leave well enough alone," Holly said. She was careful, but it did leave room for operator error by not cleaning it again. When time permits, this test will have to be rerun.
Meanwhile, Holly is going to do another test to check and see if she should shorten the time by using Fine Silver Metal Clay instead.
Testing Day 3: Firing the Synthetic Opal in Fine Silver
Holly fired the "Bermuda Ocean" Faceted Cultured Opal in Fine Silver Metal Clay at 1650º F for 30 minutes. The color is a refreshing mix of ocean tones. A soft blue and aqua green shimmering like the play of light refraction on the water's surface. Color shifts with each angle of light. She was concerned about losing the color.
Hooray! It survived! And not only that, no haze. The "Bermuda Ocean" Lab-Grown Opal color is really striking against the silver. And the color play is phenomenal. This is the moment we knew we HAD to carry these beauties.
The difference between firing the Cultured Opal at 1650ºF for 30 minutes and firing the Opal for 2 hrs is a 2% reduction of strength, so Holly, the "high fire gal," was happy with the tensile strength even still.
Plan B
If Holly can't fire the kiln for 2 hours with the 960 Sterling Metal Clay, she will need to make a base piece fired at the high temp and add the Opal with bezel in a second firing at the shorter duration. This makes this still doable, but adds an additional step.
Testing Day 4: Testing "Black Fire" Cultured Opal in a Shorter Time Span
Here is that same "Black Fire" Cultured Opal I showed earlier above, but this is a bigger 8mm faceted rose cut with the same beautiful red, orange, yellow, and green flashes. You can really see the green! It sure does catch the light at every angle. The "Black Fire" Rose Cut Cultured Opal was fired in Fine Silver at 1650° F for 30 minutes with no hazing again!!!! This means the Opal doesn't react to silver and can withstand a shorter firing time with no problems. Success!!
It was a busy day testing, and Holly also fired in place the "White Iridescence" Cultured 8mm Faceted Rose Cut Opal. This gemstone has a white translucent body ranging in a spectrum of periwinkle blue, sunny yellow, fiery orange, and red colors. It has a magnificent play of color flash consistently changing under different light and angles.
It was fired at 1650º F in Fine Silver Metal Clay. Holly enjoyed playing around with the bezel settings, first by adding tiny dots to embellish the bezel surrounding the "Black Fire" Rose Cut Cultured Opal, and then by carving into the bezel with a conical file for the "White Iridescence" Faceted Cultured Opal.
Testing Day 4: Torch Firing
Holly used Fine Silver, "White Iridescence" Faceted Cultured Opal, and a handheld butane torch. The design was made with one of her own drawings and a Photopolymer plate technique such as in her Jazzy Jewelry Class.
Torch Fired* Cultured Opals worked with no problems!!!! The Cultured Opal is as beautiful now as she put it in. She fired it for 5 minutes in Fine Silver starting the count down once the smoke was gone and the flame went out. Holly fired in a bowl of vermiculite because it was curved and didn't want it to slump, and it could have just as well been fired on a kiln brick if it were flat. There was no quenching afterward; she just let it cool on its own.
*Not all varieties of Fine Silver are torch fireable, such as PMC standard.
Tumbling Lab-Grown, Synthetic or Cultured Opals
Holly does not tumble Cultured Opals in steel shot and has discussed this with others in the know. We are aware natural opals are too soft at 5 - 6.5 on the Mohs scale, and even though this Cultured Opal is 6 -7 on the Mohs scale, it is not recommended.
We've been running on an energy high because Fire-in-Place Cultured Opals have opened the door to our imagination. Stay tuned for Part II as we will have more testing results, including other clays, such as Base Metal Clays, along with different kiln conditions and carbon firing.
You will find the New Cultured Opals on the Healing Phoenix Lapidary Website.
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