Faceting Mexican Fire Opal

By Mark Oros & Jim Perkins

Remember those thin, tall water-filled jars packed with red, orange, and yellow gemstones at the Gem and Mineral Shows? Their vibrant colors and flashes of rainbows tempted you to pay your hard-earned money for the hidden treasures within them. This is how I was first introduced to Mexican Fire Opal. When I arrived home with my newly found treasure, I opened the jar and sorted out the more valuable stones of my gem show bounty. Both Jim and I have been in love with this gemstone from the first time we saw it.

Jar of Vintage Opals

What we love about this gemstone is its color. No where else can you find the intensity of reds and oranges for the price as you can find with Mexican Fire Opal. The color is outstanding, but so is the clarity and the workability of this stone.Traditionally, opaque opals where carved into cabochons, but over the years, translucent opals have been faceted have found their way into the gemstone market. Faceting opals is a passion that both Jim and I are excited to share.

Old Stock Rough Opals for Faceting

Although we have never meet in person, our passion for faceting gemstones has brought us together several times over the past years to work and play together within the lapidary world. Jim’s recent faceting book, “Faceting with Jim Perkins,” is full of wonderful faceting instruction, tips, and faceting designs and concludes with a well thought out design for an opal round brilliant. Upon seeing this design, I was immediately driven to facet it and was more than delighted with the results. A conversation then ensued between Jim and me that resulted in the idea to write an article about faceting Mexican Fire Opal along with accompanying designs.

Faceted Mexican Fire Opal

It was fortuitous given that I had a stash of beautiful Mexican Fire Opal that I facet and sell to other faceters and Jim was interested in creating more designs for this extraordinary gemstone for upcoming books. What follows are opal faceting designs by Jim and tips on faceting this colorful gem by both Jim and me.

As explained by Sharon in the “Smokin Stones” article, there are many variations of this gorgeous opal, from red, orange, yellow, white, and every color in between, along with non-flash, flash and contra luz phenomena. It is both the variety and saturation of this gemstone that makes it a favorite with the lapidarist.

Selecting the rough opal
Mexican Fire Opal has been known to craze. This is the formation of small cracks on the surface. It can also haze or get cloudy over time. This is why we recommend buying dry opal rough that has been out of the ground for at least one year. By doing this, you will significantly reduce the chance of crazing and clouding. Ask your faceting rough provider if this is the case with the opal before you purchase it. If you cannot find old stock opal rough, then hold on to your finished faceted opals for three months before you sell them. If there is going to be a problem with newly mined and cut opals, they will usually exhibit problems within three months.

Rough Transparent Opals

Orienting and dopping the opal
When orienting the opal for maximum yield, you want to be aware of the following.

Zoning - Mexican Fire Opal can have some dramatic zoning. Be sure to place the deepest color in the culet.
When the opal has flash or color play, polish several faces on the opal rough so you can orient the flash through the finished stone’s table.
Contra Luz opal is an opal that will only show color play when the light is shined from behind it. While shining a light from behind the opal, polish several faces on the opal rough so you can orient the flash through the finished stone’s table.

We prefer to use glue when dopping opal to avoid heating the gemstone and clouding it. Opals are 5% to 30% water and the heat can evaporate the water within the opal and make them cloudy and lose flash. I prefer LOCTITE 404® Instant Adhesive, but there are also less expensive instant glues that will work.

Zoned opal that needs orientation for dopping

Faceting the opal
Opal is considered to a be a relatively soft stone for faceting; it is 5.5 on the Mohs hardness scale. We find Mexican Fire Opal can vary greatly in hardness and toughness. When you first start faceting the opal, get a general idea of how hard it is and pick an appropriate grit lap to shape the opal. We usually start pre-forming the opal with 360 to 400 grit laps, although the Hyper-Edge 250 grit is a good lap to start on a large opal. Smaller, softer opals can be formed at 600 grit. Be careful, a small stone can disappear quickly. You can usually bring your meet points in with the pre-polish lap of 3,000 to 8,000. We advise leaving the girdle slightly thicker than other gemstones due to the the softness/brittleness of Mexican Fire Opal.

Opal dopped and ready to facet

Polishing the opal
Opal can be polished using several methods. Here are several ways that we have used in the past.

Mark’s favorite way to polish opal is with the Hyper-Edge 25,000 grit. He sets the lap speed to number two on his ULTRA TEC V5 and supplies plenty of water.
Jim’s favorite way to polish opal is with a Spectra Dyna-Lap.

Another fine way to polish opal is with the GEARLOOSE CREAMWAY™ lap with BATTSTIK™ Zirconia added for a little extra bite.

Polishing Opal girdle with the Hyper-Edge 25,000 grit lap

Purchasing faceted Mexican Fire Opals
When purchasing finished faceted Mexican Fire Opal for jewelry or collecting:

Be sure that the opal has been out of the ground or faceted for at least 3 to 6 months in order to avoid the small possibility of crazing and cloudiness.
When in doubt of authenticity, have your opals tested by a Certified Gemologist Appraiser. Unfortunately, I have had clients bring me pretty red and orange plastic pieces which were sold to them as Mexican Fire Opal.

Check to see if the girdle is cut too thin. Many mine-faceted opals have very thin girdles and chip easily when setting.

Various color Mexican Fire Opals on dops with crowns finished

Conclusion:
Mexican Fire Opal makes wonderful faceted gemstones. They offer rich red, orange, and yellow colors at an affordable cost. Although your jar of Mexican Fire Opals looks great, keep them in the jar and purchase properly dried and faceted gemstones from your professional lapidarist.

Jim Perkins’ Books can be found at www.northcoastlapidary.com
Mark Oros’ Mexican Fire Opal rough can be found at www.hashnustones.com

Note: You can learn about faceting Ethiopian Welo Opals in Volume 68 Number 4, “Faceting Welo Opals” of Lapidary Journal and Jewelry Artist

Array or colors of faceted Mexican Fire Opals