by Tom Herbst

I designed O-Pace during April 2003, inspired by a piece of Contra-Luz opal and the colours of protest flags over here in "old" Europe.

Feel free to change (or omit) the frosted facets to suit your particular viewpoint - we should all leave politics at the shop door.

The design is a simple brilliant type that windows intentionally to allow a better play of colour against a dark background. I used GemCAD and BOG to try to maximize the number and effectiveness of the light rays passing through the fiery regions.

In normal lighting, there is a subtle play of colour in the gem (top image), but when things are just right, the stone lights up with fire (bottom image).

It became clear that I would need to mount O-Pace with a dark background for maximum effect. I ground a thin disk of North Carolina black tourmaline (schorl) and epoxied it to the back of a standard Tripps-type mounting containing the gem. All in all, it worked very well (see pictures below).

Several days after cutting, a couple of cloudy regions began to form in the opal. The dealer claimed that it had been dry for many months, and I waited an additional 4 months before starting on it. Six hours in water restored the original clarity, but it looks like this one will have to be stored in water.

O-Pace is a straightforward design suitable for all skill levels.Cut the frosted facets on a stationary lap, since they come in very quickly!

At right is a 13 mm 4.7 carat O-Pace cut in Mexican Contra-Luz Opal.

GemCAD and GemRay output for Green Flash appear below. The GemCAD file is available here.

Silver mounting and North Carolina schorl for the backing stone

Grinding the backing stone

Mounted opal and backing stone epoxied in place

Final necklace

Note that this design was not optimized for face-up brilliance. The rays entering the crown facets around the table are directed through the fiery regions in the opal.