Dust Devil Mining Company

Although sunstone has a critical angle of 41 degrees, and some references recommend culet angles of 43 and up, in our experience a culet angle of 45 degrees gives the best performance.

Cleavage seldom gives any trouble in sunstone. Most often, it is best to orient stones according to color and schilller first, then according to yield, leaving cleavage as the last concern.

In a given stone, if cleavage is to be considered, orient the cleavage plane seven to ten degrees away from the table.

Note that on occasion faces that fall close to the cleavage plane may feel softer, cutting somewhat faster than their neighbors. If you experience this, use a light touch and be prepared to consider the tips on polishing given below.

Color in sunstone usually occurs in a bulls-eye pattern - a spot of color surrounded by a clear or light straw-colored rind:

This beautiful carving by William Cox displays the natural color distribution pattern common in sunstone:

The best color performance for faceted stones is achieved by focusing the available color at the culet of the stone and placing as much color as possible in the pavilion:

Such orientation will cause light that enters the crown to reflect through the color zone before exiting the stone. This stone was cut with such orientation:

Alternately, if the size and placement of the color zone permits, orient it beneath and parallel to the table:

The bulls-eye pattern is also seen in multi-colored stones. The "watermelon" pattern shows a red core, surrounded by a green covering, followed by a clear or light straw-colored rind.

Multi-color stones require careful orientation (and some luck) if they are to produce pleasing colors. Use a polarizing filter to examine colored stones. A stone that looks only red (left photo below) may show a wonderful watermelon pattern when viewed under a carefully-aligned polarizing filter (lower photo below).

Incorrect orientation (or poor luck) can mix the beautiful red and green into a muddy brown...

In our experience, the best color performance is achieved by orienting the stone so that the greatest saturation of green will be seen through the table:

With care and some luck, the colors will remain independent, producing results like these two stones:

In evaluating rough for schiller, it must be remembered that faceted stones sparkle by transmitting light while schiller sparkles by reflecting light. Once a light ray is reflected by a plate of schiller it will no longer be available for the stone to refract and transmit. Also, lit from behind, schiller can only cast a shadow.

In this photo, streaks of schiller appear as copper-colored shadows. Because they are lit from behind, the schiller can only cast a shadow toward the viewer:

The same stone, with the schiller lit from an angle to reflect toward the camera presents a dazzling display of fireworks - even in a rough stone:

True snowflake schiller has a seemingly random distribution within the stone, and can be oriented for best flash or overall color.

However, it is important to evaluate the stone carefully to insure that the rough is not overpopulated by flakes of schiller, or you may experience a "white-out" as shown in this magnified view of an emerald cut sunstone (50-X magnification):

In the above example the schiller absorbs too much light, starving the stone's pavilion faces for light to reflect. What light is transmitted is absorbed by other schiller particles, which cast shadows toward the viewer. This stone should have been cut en cabachon.

Well selected and oriented snowflake schiller will give a glitter-globe effect and perhaps a pinkish glow in the finished stone:

Stripe schiller should NOT usually be oriented parallel to the table as this will often absorb too much light and cast shadows, darkening the finished gem:

One exception to this generalization is very light stripe schiller, seen below at both 50-times magnification and at 1-X. Easily overdone, this light, wispy schiller can lend a pink color and perhaps some interesting patterns to the stone.

A better use of this kind of schiller is to orient it perpendicular to the table of the stone, as shown in the next section on "kaleidoscope schiller".

Another exception is the use of schiller stripes to accent the appearance of a stone. Here, stripes of silver schiller accent an emerald cut sunstone:

Stripe schiller is often oriented close to 45 degrees from the table of the stone as shown in this diagram:

This orientation causes the schiller to flash as the stone axis moves away from the viewer, creating an exciting effect. If the schiller is not too dense, it will allow sufficient light to pass for the stone's pavilion to perform. This angled orientation can accent the depth of the stone, giving the appearance of an independent light source within:

In another example of 45 degree orientation the schiller stripes are clearly visible through the side of this emerald cut sunstone (50-X magnification):

he schiller stripes in the above example are reflected in the pavilion faces of the stone, creating the winged pattern which is seen below at both 50-X and 1-X magnification. This presentation could be called "kaleidoscope schiller":

This term is for schiller (usually with well-defined stripes) that is intentionally oriented to create patterns by reflecting in the pavilion faces of the stone as shown above. The most common orientation used to build this effect is parallel to the center axis of the stone (perpendicular to the table):

Lighter schiller oriented in this way can produce a very pleasing warm pink glow throughout the stone while stronger stripes can kaleidoscope.

 Because no two stones are schillered just alike, each stone is truly a one-of-a-kind work.

Varying colors, intensities, and angles of schiller offer endless opportunities. The following 50-X magnification of a simple round brilliant cut shows both silver and copper schiller chasing each other in a wild dance of colors and patterns. This is why sunstone is so exciting to work with! (50-X magnification)

Opaque schiller is probably most often oriented nearly perpendicular to the viewing axis of the cabachon or rose-cut stone (parallel to the table):

With the exception of very deep opal or opal triplets, the deep colorful reflective effects of Oregon Sunstone with opaque schiller are unrivaled.

Sunstone generally cuts easily, giving no trouble at any stage with any grit of lap. The occasional exception is the unraveling of a cleavage plane.

Reversing the travel of the lap and/or changing to a different grit lap will usually solve this rare problem.

The only other caution is that faces that fall close to a cleavage plane sometimes cut significantly faster than their neighbors, necessitating a careful touch.

After cutting with a 600 lap, sunstone typically produces a brilliant polish quickly and easily with cerium oxide paint on a dynalap or plexiglass lap. Prepolishing with a 1200 lap will allow even faster results.

Two other difficulties are scratching and unraveling of a cleavage plane.

As with any gemstone, scratching can be caused by insufficiently charged lap, inappropriate speed / pressure, etc. Addressing these common variables will usually address the scratching issue.

However, there is a unique scratching issue with sunstone. Scratches can originate where individual particles or clumps of schiller breach the surface being polished.

This can usually be remedied by reversing the travel of the lap, and perhaps varying pressure or "squiggle" technique. A finer prepolish such as a 3000 lap seems helpful as well.

Very occasionally, a face will begin to unravel. Often, simply reversing lap direction will solve the problem. But, sometimes prepolishing with a 3000 lap will be necessary in addition to the reversed lap direction upon resuming polishing.

This page was written by John Bailey at www.GemstoneArtist.com. Your questions and comments are welcome!