My favorite stones to work with

Precious Opal
Unlike other gemstones opal does not have a crystal structure, and the texture consists of amorphous silicon dioxide having submicroscopic silica spheres. Depending on the size and how these silica spheres are arranged together determines how they diffract light. These silica spheres have diameters that range from 0.15 to 0.30 microns (one thousandth of a millimeter ) which is a little smaller than the wavelength of visible light which ranges from 0.4 to 0.7 microns in diameter. In order for opal to be considered precious opal the silica spheres must be uniform in diameter and arranged in neat rows. A precious opal that has flashes of red will also contain all the other colors of the spectrum as the opal is seen by all other angles. It is interesting to know that this structural color of opal is produced by light, conveyed by the eye and is then understood by our minds.
To this day I am fascinated on how challenging Natural Opal is to cut and polish. Since I know that Opal with flashes of red and yellow are highly prized I do my best on keeping as much of these colors as I possibly can into an opal cabochon or incorporating it into my inlay designs. Generally, if I am inlaying natural opal I will design the jewelry around the stone so there is minimal cutting of the opal. I never know what the stone will look like until it is finished. As I get more experience grading opal, all other types of stones that I work with become naturally easier to work with. I have realized that all types of natural opal are magnificent gemstones and display unique characteristics. But out of all the natural opal in the world there is only a couple types of opal that I am comfortable in using.
The most prized natural opals that I use for my jewelry inlay is natural Opal from Australia and Brazil. Like Australian Opal, Brazilian Opal has a very good reputation for producing some of the most stable and precious natural opals in the world. Both types of Opal are similar in both their colors and intensity of the play of color. All natural opal has a Mohs hardness that ranges from 5.0 to 6.5 which are considered to be softer stones. Suprisingly, Brazilian Opal is hard to distinguish between opal from Andamooka, South Australia. They both have a similar hardness and contain the same play of color with a light background.

Brazilian Opal mainly comes from the Boi Morto mine. Boi Morto means “ox dead” in Portugese. This name came from an ox that fell off a cliff and died at the base of the opal occurrence during early opal prospecting of the area in the late 1900’s. This Boi Morto Mine is around the area of Pedro Segundo (Pedro II), which is a small town in the state of Piaui’, in Northeastern Brazil.

The Australian opal, mostly known as Black precious opal, comes from Lightning Ridge in New South Wales, Australia. This type of natural opal has a very distinguishable look compared to other types of opals. This stone was given the name Black Opal due to the stones dark background color. It is like a colorful rainbow flashing light in front of a black night sky. Black Opal from Lightning Ridge is considered the rarest and most prized opal in the world. After working with this magnificent gem, I found that it is more stable than most types of natural opal.

I purchase these types of natural opals in small parcels of opal rough. Each opal nugget has clay coatings and potch (common opal) around the lines of fire. This needs to be either ground or cut to expose what is inside each piece of rough. Once the lines of fire are partially visible they can be graded and classified into certain categories such as cabochons or inlay pieces.

When finishing opal I notice that any type of contamination or minute mistakes will show up on the finished surface. I make sure that before I set an opal that the surface has a fine polish and that the back of the stone needs to be ground to the desired depth. It is common for other jewelers to mix dark dye with the epoxy to give the opal a better brilliance of color. I will use the same method but it depends entirely on the stone that I am setting. When I set a rare Black Opal into a deep channel there is no point in enhancing the color with dye. If you are interested in Natural Opal, then why not be interested in the finest opal in the world?








Lapis Lazuli
Lapis Lazuli is one of my favorite stones to work with because it has very nice color and is also challenging to work with. What I have found with this stone is that more Pyrite that the Lapis contains, the more vulnerable it is to fractures. I generally cut a lapis stone into small slabs about 3mm and let the slabs sit in paraffin wax under a heat lamp with moderate heat. I use the a 220 grit soft back diamond wheel to shape this stone since this wheel has cushion, and if I want to inlay into a straight sided channel, I will lightly hit the side of the stone on the 220 steel back wheel which will always give the stone a perfect straight edge. The advantage of a straight edge on any given stone is that it looks more professional especially when inlaying multiple stones next to each other. The channels that I inlay are a little over 2mm in depth which me plenty of room to work with. The glue that I use is industrial strength epoxy gel type glue where the consistency is thick enough to remove easier with an exacto blade and lightly sprayed with a glue accelerator. Once the stone is inlayed and the glue is cured, the grinding begins. I will grind away the stone starting with an aggressive will such as a 220 and step down to 600 grit, then I start the polishing with the 1200 grit up to the 3000 grit wheel and then firmly hit the stone on a sapphire powder lap. After each step of grinding and polishing I always check for fissures or cracks. If any exist, you'll need to remove the stone and start the process from the beginning. I hope this can be of some help for you novice inlayers.