The Prez Sez: Montana Sapphires

By Nancy Attaway
 
 

Montana sapphires rank as one of America's finest gemstones, highly valued in the gem market for their fine quality and great beauty. Found in glacier deposits of sand and gravel, these river-worn stones exhibit a rich diversity of color. The high concentration of iron and titanium in their chemical makeup conveys a unique range of hues that include blue, teal, red, pink, yellow, orange and lavender. Some Montana sapphires exhibit color change phenomena, and some are bicolored. The unique color banding present in the crystal structure acts as a signature of authenticity as a natural sapphire, another plus for these wonderful stones. The clarity of Montana sapphires allows for a brilliance usually associated with gems of much higher index of refraction when they are properly cut.

Sapphire mining in southwest Montana evolved from the gold rush of the 1860's. Drawn by the promise of vast riches, people traveled great distances to search for the yellow gold of Montana. Those prospectors with gold mining experience
in California constructed wooden sluice boxes to separate the gold from the river gravels. Being heavier than the gravel, colored "pebbles" sank to the bottom of the mix and collected behind "riffles " in the sluices. As experienced placer gold miners, these men noticed the unusual small differences in the heavy minerals concentrating in their sluice boxes - like the little, colored translucent pebbles seen here but not seen in California. At first, they simply discarded these "nuisance pebbles" clogging their sluice boxes. Eventually, one miner sent some of these pebbles to Tiffany and Company of New York City. where they were identified as sapphires. The rest, as they say, was history. Sapphires had been discovered in southwest Montana. However, gold continued to captivate the minds of the miners, greatly overshadowing the discovery of sapphires.

Most of Montana's sapphires originate in two main localities. One is located on a bend of the Missouri River near Helena. The other is located at Gem Mountain, just west of Philipsburg some 50 miles or so northwest of Butte. The sapphires are usually recovered from beneath 20 to 30 feet of barren overburden along river banks. They are sifted and picked from the gravel concentrate. The sapphire deposit at Eldorado Bar (along the Missouri River) come from a rich alluvial gravel deposited long ago at the foot of a retreating glacier.

In the 1890's, a group of English investors acquired 3,900 acres along the Missouri River that included the Eldorado Bar. Their intention was to placer mine for gold and sapphires. Work, however, was soon suspended for two reasons. First, the gold output was not of itself sufficient for profitability. Secondly, most of the recovered sapphires were pale blue and attracted little interest in the gem markets of the time. Marketing the new Montana sapphire hues proved difficult in an era when the classic royal blue color stood as the benchmark of comparison in all of Europe. The lack of an American cutting and marketing organization also contributed to the problem of promoting these paler colored sapphires.

As gem cutters, we know firsthand that the beauty and value of a gemstone is only realized after it is properly faceted. In the late 1800's and early 1900's, America lagged far behind Europe in the art and technology of gemcutting, though a few cutters were beginning to appear in New York City. Without a strong vertical domestic market, Montana sapphires depended on European expertise to realize their potential. Ownership of the several sapphire properties of southwestern Montana changed hands a number of times before new technology enabled these gems to become valued and appreciated.

The advent of heat-treatment in the 1970's established a vertical market for Montana sapphires. In the 1950 's and 1960's heat-treatment technology was being developed and applied by growers of synthetic materials for use in lasers. Heat-treatment improved the laser properties of lab-grown sapphire. More or less coincidentally, it also improved the color or added color where none had existed prior to treatment. The process soon became essential to the sapphire market and presented new possibilities for marketing Montana sapphires. John Emett (of Capital Research in Pleasanton, California) and his student, Brian Kvasnik (now with Gem Resources, Inc. In Minneapolis, Minnesota) are the chemists credited with finding new methods for improving and altering the color of Montana sapphires.

During heat-treatment, elements within the crystal are re-aligned, and the valence states of iron and titanium contained in the crystal are altered. Computer-controlled electric furnaces hold temperatures near the melting point of sapphire (2, 050 degrees centigrade) in a controlled gaseous atmosphere. Any rutile within the sapphire is dissolved. After a predetermined time at high temperature, the temperature is very slowly brought back to room level. At this point, the treatment is complete. If any color change can be made by heat-treatment, it has been made and will be permanent.

At the 1996 February Tucson Gem & Mineral Show, Moss Aubrey, Steve, and I split a Montana sapphire purchase of Eldorado Bar rough. The parcel had been a portion of a mine-run lot a dealer had purchased when Sam Speerstra operated that Eldorado Bar claim. The sapphire rough from our parcel took form in several different ways, as not all of the pieces had the same appearance. Some maintained their hexagonal shapes as worn six-sided cylinders. Others were flattened prisms with orange spots at the centers. Many were like stream-tumbled pebbles, shallow and chunky. The hues varied from pale blue to deep blue, pale yellow with orange centers, pale green, and lavender. A few of the flat, tabular hexagons exhibited a raised triangle atop one flat side.

To date, I have faceted seven sapphires from my share of the parcel: one square, one long thin emerald cut, four rounds, and one freeform. The pavilians of two of the rounds were cut at topaz angles: 51 degrees at the table breaks, 41 degrees for the mains at the culet, and 46 degrees for the intermediate pavilion facets. The pavilions of the other two rounds were cut at angles one degree below each of the topaz angles. All four rounds were cut to a twelve-sided design, my favorite for round gems. This design is a variation of one developed by Reg Thompson of Petaluma, California. He named it the Spectrabril. The variation I used is called the Flasher Cut. True to its name, it returns excellent brilliance from stones as small as 4 mm and as large as 16 mm. These lovely round sapphires with the Flasher Cut measure 7 mm, 6 3/4 mm, 6 mm, and 7 mm. The first three mentioned are a lovely deep denim blue. The last one mentioned is pale yellow with an orange center. I was especially curious about how the orange color would look in the center of a Flasher Cut round. I was not disappointed. The orange color flashes across the stone as it is moved and flares out from the crown facets. Nice!

My square sapphire is 7 mm on a side. The cut is the Square Barion by Long and Steele. As many of you know, the famous diamond cutter, Basil Watermeyer, invented the barion designs specially for the diamond trade. Strangely enough, his new design was not embraced by the majority of the diamond cutters. However, he certainly grabbed the attention of cutters of colored gems, particularly the amateur cutters, when the barion principle was applied to squares, rectangles, cushions, triangles, and ovals.

For my 7 mm Square Barion Montana Sapphire, I adjusted most of the angles to accommodate the rough. Sometimes the cutter must make these adjustments because the rough dimensions may limit finished stone depth. In my case, I changed the large pavilion barion facets from the customary 65 degrees to 60 degrees; the normal 44.6-degree pavilion corner facets became 43 degrees; the eight long pavilion facets normally at 44.5 degrees became 42 degrees, and the little culet facet angles dropped to 41 degrees. These adjustments changed the pavilion appearance somewhat, but the effect remains dazzling to the eye. My square is a nice shade of denim blue.

My long, narrow step cut sapphire had been a glacier- and river-tumbled cylinder that had had the hexagonal original crystal shape completely worn away. When I got it, it was shaped like a medicine capsule. After cutting to establish the girdle dimensions at 10.5 x 4 mm, I step cut the pavilion and crown facets. Actually, the pavilion facets consisted of a few just below the girdle. The bottom was essentially flat. It lacked depth for a conventional pavilion, so I flattened it so Steve could carve a series of shallow, triangular grooves into the flat. This created a series of shallow pavilions that reflect light back through the crown while adding interest to the appearance. This stone, too, is a nice denim blue color.

My freeformed sapphire started from a rough, flattened, hexagonal prism. It was pale yellow with a large, orange center area. An idea occurred to me for incorporating the existing shape of the rough, and I decided to experiment. The tabular rough exhibited six distinct sides. With the 96-index gear in place and the angle set at 90 degrees, I located the six sides of the crystal at indices 96, 81, 15, 63, 30 and 48. These were cut to form a girdle, but a gouge remained at one edge of the index 48 facet. Facets cut at 42 and 54 took care of that. Step facets were then cut at the girdle indices at angles of 48 and 43 degrees, leaving a large flat culet area. The crown was step cut at angles of 40, 30, and 20 degrees, leaving an oversize table. To my surprise, the orange center splash bounced all around the crown facets. The finished stone also revealed that the orange center actually consisted of a very deep orange centerpoint surrounded by a paler orange cloud. Steve carved a sunburst design into the flat pavilion area to finish the stone, which will become a part of pendant I am designing. I still have several of these tabular crystals of various sizes and plan to cut them into sets for matching pendants and earrings.

I now realize that in faceting Montana sapphires, the factors of limited depth and the color concentration both need to be addressed and are as important as selecting the appropriate cut design. All of these considerations must mesh well together to yield sparkle, best color, and to maintain as much carat weight as possible in the finished gems. Those are the reasons why I found it necessary to adiust the normal cutting angles listed with published designs and why inventive designing and design altering are important. The chosen faceting design must utilize the unusual shapes of the sapphire rough and compliment the sparkling beauty of these gems. A little thought will enable the serious faceter to increase the interest and the yield from a parcel of mixed rough sapphire from Montana's Eldorado Bar. It works for me.

Nancy Attaway
 

Some comments:

   I was quite impressed with your page on yogo sapphire. I did however find one common error. The myth that princess Diana's ring is yogo. This was caused by Intergem hype promoting them as royal american sapphire. Yogo is the best of the best and can stand on it's own without royalty. See http://www.3rivers.net/~dbaker/diana.htm
   If you have a source to get any rough I would be very interested. They are very hard to come by. I have been cutting them for 30 years. You may want to check out my site at http://faceter.net
 
James Rambur