Cutting Tips for Oregon Copper Bearing Sunstone
Images on this page courtesy of John Bailey, gemstoneartist.com
On this page you will view and understand the orientation of Schiller and Color in Plush Oregon Sunstone a copper bearing Feldspar. Plush Sunstone from Oregon is a genuine pleasure to work with. At a hardness of 6.8 to 7.2, Plush Sunstone cuts and polishes quite nicely and each stone is unique and pleasure to ware and view when finished. Enjoy and use the following information.
CUTTING ANGLES for Oregon Sunstone
Oregon Sunstone has a critical angle of 43.5 degrees, and some references recommend culet angles of 43 and up, in our experience a ulet angle of 44 to 45 degrees gives the best performance in a round brilliant cut.
ORIENTATION OF CLEAVAGE
Cleavage seldom gives any trouble in Sunstone. Most often, it is best to orient stones according to color and Schiller effect first, then according to yield, leaving cleavage as the last concern, which only becomes a problem if you jam the stone while cutting. 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. As with all rough If you experience this, use a light touch.
ORIENTATION FOR COLOR
Color in Sunstone usually occurs in a bulls-eye pattern – a spot of color surrounded by a clear or light yellow 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:
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, 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 can mix the beautiful red and green into a brownish color tone. In our experience, the best color performance is achieved by orienting the stone so that the greatest saturation of green or red will be seen through the table:
With care the colors will remain independent, producing results like these two stones:
ORIENTATION OF SCHILLER
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:
Speckle Schiller
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 cabochon.
Well selected and oriented speckle Schiller will give a glitter-globe effect and perhaps a pinkish glow in the finished stone:
Banded or Barred Schiller (Stripes)
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 “Feather Schiller”.
Another exception is the use of feather Schiller to accent the appearance of a stone. Here, stripes of feather Schiller accent an emerald cut Sunstone:
Some times Feather Schiller is often oriented close to 45 degrees from the table of the stone to get the strongest, or lightest effect, 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 to the barred Schiller stripes are clearly visible through the side of this emerald cut Sunstone (50-X magnification):
The 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”:
Opaque AAA Schiller
Opaque Schiller is probably most often oriented nearly perpendicular to the viewing axis
of the cabochon 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.
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