Bi-Color Montana Sapphire

Posted on Dec 22, 2014 in Gemcutting, Journal, Transformations

Recently I was commissioned to facet a very large and unusual sapphire from the El Dorado Bar diggings in Montana, USA. The stone came to me as a 3.17g rough. As it pretty typical for the Montana deposits, the stone was water-worn a crystal section. Unusual for the Montana deposits, the stone has a straw-yellow body color with a pink color zone nearly centered in the rough. The local miners call this a “color seed”.

MT Yellow/Pink Sapphire Rough

A 3g rough is a very large, very rare rough from the El Dorado diggings; in fact, it’s large for Montana sapphires in general. I’ve cut quite a few US sapphires, but have never had the chance to cut an 8×10 stone:

MT Yellow/Pink Sapphire Rough with template

My client wanted the stone to have a custom-cut look, but she was also very keen for me to retain as much of the stone’s weight as possible. To meet both goals, I applied a cutting technique that is more common to tourmalines than sapphires. By cutting a hard rectangular outline and utilizing a keel rather than a culet, I was able to retain as much weight as possible. But unlike tourmaline, the high refractive index of sapphire allowed me the freedom to manipulate the facet placement and angles to make this stone pop.

Happily, I was able to meet my client’s spec — the stone came out to 5.02ct., 8.48 x 10.02 x 6.00mm. That’s a 31% yield — a very respectable yield for a custom-cut US sapphire!

I was very pleased indeed to hear: “She got it today and was showing it off to everyone. Totally loves it.”

MT Yellow/Pink Sapphire in tweezers

MT Yellow/Pink Sapphire

MT Yellow/Pink Sapphire