What is Arizona Black Jade?
This black jade is from a fairly recent find in Arizona, USA, which isn’t a traditional producer of jade. While this material is called black jade, it’s very slightly different than traditional jade. Technically, this material has two copper molecules that normal jade doesn’t have.
For all practical purposes, this material is black jade and works like any jade I’ve ever cut, except this material is easier to work and polish than a lot of the jade I’ve used. Its hardness is basically the same as jade and it really does work well and polishes easily and nicely. (If you’ve cut jade, you know this isn’t always the case).
Is Arizona Black Jade Really Jade?
Editor’s note: Black jade does occur in both nephrite and (more rarely) jadeite varieties. However, consumers should be aware that material sold as “Arizona black jade” is likely neither jadeite nor nephrite. Some of this material has proven to be iron-rich hornblende, despite specific gravity and refractive index values that match those of jadeite. Although hornblende, like nephrite, belongs to the amphibole mineral supergroup, it’s not nephrite.
You might encounter prospectors and vendors online who make guarded claims of hidden sources of nephrite in Arizona. Buyer beware. Nevertheless, a poster on the Rock Tumbling Hobby Forum found an article from the June 1983 issue of Rock & Gem that reports on an unusual nephrite discovery in the Mogollon Rim area of Arizona around 1970. Of 14 suspected samples sent to the Smithsonian Institution for identification, one reportedly proved to be nephrite. Some other samples were described as “nephritic.” Geologist Lee Hammons estimated the Arizona nephrite find at 1,000 tons, though it would be very difficult to reach.
The nephrite apparently formed in a non-typical manner: as a thin layer between diabase and clay. The material in contact with the clay became nephrite. The upper layers became “nephritic diabase,” not true nephrite. Both materials can be carved, but the article extols the lapidary properties of the “nephritic” material, above and beyond those of the actual nephrite.
Identifying black opaque gem materials can be difficult, and a consumer may find it particularly challenging to distinguish actual nephrite from “nephritic” material — or jade from jade “for all practical purposes.” Ask vendors to specify the nature of any Arizona black jade they sell. Although the jade-like material may have better carving properties, jade has the name power to encourage sales.
The Cabbing Machine
There are many types of cabbing machines on the market. The type of work that you want to do will determine what type of cutting machine you need. Here, Jason is setting up a pretty standard 6″ cabbing machine.
Although the unit Jason is using is designed mainly for cabbing, not traditional carving, this machine can do some modest carving/cabbing with a little adjusting and some expert experience.
Jason’s pendant is mostly a cab. However, he used some carving techniques to create its flowing lines, curved top, and slightly concave back.
Carving generally requires a Foredom or similar tool or a fixed arbor with a drill-type chuck to hold various types and shapes of diamond and carbide carving bits. As you’ll see later, Jason also used a Foredom to drill the pearl hole and polish the pendant
Although you can use a diamond bit, an ultrasonic drill is by far the best way to drill.
To the right, you can see Jason has 100, 600, 1,200, and 3,000 grit wheels on the machine from left to right. This machine uses 6” laps. Others use 8” laps, but you’ll find 6” laps used predominantly in cabbing because of cost.
Notice that the fine grit wheels are all different colors. The colors designate the lap’s grit. While this is a general rule of thumb, remember that grits and colors will vary from manufacturer to manufacturer.
The types of laps you would need to use depend on the type of material you’re cutting. Of course, you can easily change the wheels, assuming you have the other wheels on hand. Jason’s setup for this Arizona black jade pendant is pretty standard for most commonly cabbed/carved stones.
Shaping the Arizona Black Jade Pendant
Drilling a Hole for the Pearl Pin
There are several ways to drill a hole for the pin that will hold the pearl. Normally, you would use an ultrasonic drill, because that type of drill makes such a clean, easy hole. However, Jason didn’t have an ultrasonic drill at the demonstration. These tools are expensive and delicate, which makes them difficult to move.
So, he used the next best thing, a Foredom and diamond bit to create a hole for the metal pin that will hold the pearl.
Both the pin and the pearl are friction fit and glued on the finished pendant. However, the pendant has to be completely finished and polished before this last step.
Final Touching Up and Shaping
After drilling the hole for the pin that holds the pearl, you must do some final touching up and shaping with the fine pre-polish wheels.
Doing some final touching up before polishing is a very good idea, because it’s easy to miss something (like scratches and flat spots) before polishing.
In particular, Arizona black jade needs a final once-over, since the material’s black color can hide imperfections from casual observation. Examine any black jade very closely before moving on to the polish.
Polishing the Pendant
After finishing touching up the pendant, Jason used a Foredom with a felt buffing wheel and aluminum oxide to polish the pendant.
You can polish a pendant like this in several different ways, but you’d use a Foredom in most cases. However, if Jason were at home in his workshop, he would use a large, leather, foam-padded wheel at slow speed to polish the larger flats and domes of this pendant. (The Foredom would still be used to polish the smaller, harder-to-reach places on the pendant). It just takes longer to polish the whole pendant with a Foredom. It makes no difference to the final result.
As you can see in the photo below, you’ll use a thick slurry of aluminum oxide during polishing. The polish is 0.5 microns (very fine) and mixed like a very thick paste.
Use the Foredom wheel at a slow speed to keep the polish from splattering all over the place. If you haven’t guessed yet, carving/cabbing isn’t a really clean hobby. Expect to get dirty.
As you can see, Arizona black jade can take a very nice, high bottle-glass polish with no problems.
You can see the hole for hanging the pendant near the top. On some materials, you wouldn’t want to drill a hole that close to an edge. However, Arizona black jade is tough and will wear well, so this won’t cause any problems.