Please see part one and part three as well

Opal rough is sold in parcels, the Australian term for any amount of opal being offered. A parcel may range from a single stone to a batch of hundreds of stones. Quality may range from "rabbit rocks", potch or matrix (or both) which is useful only for slingshots and target practice, to brilliant crystal fiery sparklers which will knock your eyes out.

Usually there is a range of quality or grades of opal in a particular parcel, although some dealers grade parcels pretty strictly, based on what they can see of the color and yield.

Total production from a mine is known as mine-run. Often offered, but seldom true. Almost all opal parcels are the result of grading and sorting the material from a mine. The top 10 percent or so of mine production is seldom seen except by purchasers of large quantities of opal rough, by buyers who deal directly with miners or miners' agents. This top quality material is usually purchased by European and Japanese buyers, who pay much more than the market will bear in the USA.

A piece of precious opal rough is valued by the percentage of precious opal present in the stone. If the stone is almost completely precious opal, it is known as skin-to-skin, referring to the outer layer of the stone, which is usually a thin layer of potch, with the precious opal hiding below. Often a miner will pinch or nip off a bit of the skin in a few places to see the color.

A piece of opal may also contain bars or bands or layers or sections of precious opal surrounded by potch. This is often referred to as P & C or potch and color. The size of the precious part relative to the potch or the matrix present is the important thing here. Banded or layered sections of precious opal may be thick or paper-thin. You may be able to cut a stone which is solid precious opal if the sections or bands are thick enough, and if the color band is relatively flat or straight. Sometimes a band of color will wander through the stone, curving or bending, and the band may thin or play out within the stone. Thinner bands may be cut with only the precious color showing on top, while the bulk of the stone may be potch.

The relative value of a piece or parcel lies in the percentage of weight of finished stone it will produce. This is known as yield or return. Most opal rough will return a relatively small percentage of the original stone. Most of the stone will be ground away in the shaping, or pre-forming process. The amount depends on the original shape of the stone as well.

Some people prefer to cut calibrated stones, which are a standard size, shape ond thickness, and will fit into pre-made ring and pendant findings, so the jewelry mount does not have to be made specifically for the stone. More opal, including precious play of color, will have to be ground away. This returns a smaller yield than if the stone is a freeform shape.

Freeform means that the stone has been cut, shaped and contoured to the boundaries of the precious opal section rather than a specific size and shape. This will naturally return a larger stone which will not be perfectly round, oval or any other regular geometric shape.

Yield may be as small as 10 percent or rarely, may be 50 to 70 percent. Higher yields may be obtained by carving the stone, but seldom over 70%. A bottom line average is about 20 to 30% although many dealers will claim higher percentages of return for a particular parcel. Keep grains of salt handy.

So a parcel of P & C should sell for less than a parcel of skin-to-skin opal of the same size and color quality, since the yield will be less. Of course, often it is difficult to determine from pictures, or even by personal inspection, just what the stone will return, since only Superman can see into the stone to determine what happens to the color.

Various opal dealers have claimed to have "X-ray" eyes and suggest that you trust them. This is not recommended, even if the dealer offers a return guarantee. All that guarantee buys you is a chance to see the stones in hand rather than just a picture.

Always decide if you want to keep the parcel before cutting or nipping or processing the stones in any way. No dealer will accept returned parcels if they have been altered in any way, such as nipping or grinding to expose the color. If you cut it, it's yours.

Often opal is nipped by the miner or dealer to show the color inside and sometimes rough will be faced or edged. This means that a section of the skin has been ground away to expose the fire below, either ground across a large section of a flat surface, or the edges may be ground away to show the number and thickness of the color bars or bands. This is called facing the opal.

If a face is ground to expose a broad section of color, the stone is referred to as a rub. Usually most of the matrix has been ground away as well. This is a good way to be more certain about what you are getting and is often recommended for beginners. Actually it is a more useful strategy for experienced cutters, as a rub may have a very thin layer of color on its face and a less experienced cutter may grind through it in the sanding and polishing stages.

Rubs will generally be more expensive than a parcel of unrubbed opal, as there are fewer surprises. This is good and bad, as part of the joy of cutting for some people is the mystery of what's inside. Others are not so adventurous.

Another way that rough opal is offered is as pre-forms. This means that the individual stone has been ground into a close approximation of its final shape and size, exposing the fire and removing most of the matrix and potch. All the cutter has to do is to finish the final shaping and surface smoothing and then polish the stone. Naturally this returns the highest yield for weight purchased and is priced accordingly higher.

Preforms are a good way for a novice cutter with a light touch to produce a good looking finished stone, but a heavy hand will leave a beginner with an expensive pile of dust and a much smaller stone than the preform was expected to produce.

Other factors in valuing a parcel include size of the individual stones, number and brightness of colors, stone shapes, the patterns the colors form and the body color of the stone.

These will be addressed in Part three ---

Thanks,

Mike Kelley

arthursonn on eBay