Let us cut tourmaline, orienting and preforming rough.

I have been writing about individual pieces and the stones that can be produced, but I hope to put down on this page a some reasonable ideas about working with different types of tourmaline rough to produce beautiful gemstones.  It will not always be the way commercial cutters would work because weight retention is not my principle objective.  Still I done’ waste material if I don’t have too.

1,  A beautiful, flawless, blocky, water worn, non dichroic pebble.

Not only is that a mouthful, but you have a great opportunity to cut the pattern of your choice from the hundreds of faceting patterns.  I like to use 41 degree mains on brilliant style cuts and 40 degrees on emerald cut style patterns, but I do not cut very complex patterns, so there are better places to go to, when the rough lets you do whatever you want to do.  This kind of rough is really not that rare and outside of wondering where the c axis is (It can cause problems in polishing for me even if it indistinguishable from the a/b xis) you should have no problems with it.

2,  A beautiful, flawless, blocky, water worn, dichroic pebble.

Unless you are dealing with a darkness problem with the rough, I do not make a great deal out of the color variations that come from the rough having two dichroic colors and or levels of tone.  Of course if the mixing of the colors really causes a muddy mess, than you work to isolate the colors by having steep ends on the pavilion facets perpendicular to the c axis, of an emerald cut.  Generally I would cut the pebble for weight retention.

3,     A beautiful water worn pebble that has  a good cross section for a round, but is too thin to utilize the complete diameter of the pebble.

I use to just put a flat on the pebble as a nascent table, which is usually on or close to the c axis since most tourmaline crystal fracture across the c axis.  And then grind down the pebbles diameter until I had enough depth to cut a standard round brilliant.  You get the most spread/shallowest stone with a standard round brilliant  (with proper angles) and I like the cut with tourmaline.  Then it dawned on my that maybe a long ratio oval (1 to 1.5 width to length) would retain the weight better.  Now,` depending on the rough, I do check both making a round out of it or an oval to pick the right one for weight retention.

4,   Freshly mined crystals.

What I have said about water worn pebbles can certainly apply to tourmaline mined from a pegmatite.  But I find much of the green rough available in fresh crystals has a long ratio and is therefor limited to some kind of emerald cut style, to cut  efficiently for the retention of  weight.  This does not apply to chrome tourmaline which does not even come from a pegmatite and tends to be pretty  blocky.  (It is metamorphic in nature)  I usually find red/pink rough to have been cobbled (broken by applying pressure to existing weaknesses.) and it is more amenable to a variety of cuts.  The rest of tourmalines many colors are probably seen more often as pebbles than freshly mined crystals.  And all colors of tourmaline water worn and fresh can be extensively ground to meet cleanliness factors by careful dealers who prepare their rough for sale.  Examine all ground surfaces on the rough carefully because many times the flaws that lead to material removal, were not ground out completely.  Breaking a crystal into sections by clipping very often causes damage and rough should be examined for this sorry condition.

5,  Rough that is well shaped to do a triangular shaped gemstone.

As long as the rough is not too dichroic, which could make one side of the three sided stone too dark, I do not worry about the orientation of shield cuts or trilliants etc. in tourmaline.  You get a lot of mixing and flash for the amount of work you have to do on a shield/trilliant cut and I use them whenever I can.  But that is not too often because many tourmaline crystals are too thin to use its cross section or has damaged corners or is just plain not symmetrical enough.

6, Long skinny crystals that have semi closed to closed ends.  I have cut these crystals with steep ends perpendicular to the c axis and with the normal angled end.  Using 70 degree angles at the girdle of the emerald cut does reduce the darkness from darker ends, but I don’t like the light movement in the gems as much as I like with the normal angles.  So I generally cut the emerald cuts with normal angles unless the tourmaline is really dense.   On top off that I don’t cut really long stones.  I either split the crystal or just grind down the ends until I get a reasonable ratio of its length to width.

7,  Short stocky crystal sections of moderately dichroic crystals.

You have a number of options with either water worn or sharp crystal sections as long as the c axis is not to dark.  It the crystal cross section is round enough you can cut a round or triangular enough you can cut a shield etc.    This way is very nice because you get a single color that is a blend of the a/b and c axis.  I can sometimes get a bit bigger gemstone by making the table at 45 degrees to both the a/b and c axis.  I find the color blending to be quite satisfactory.  Or you can cut a round with the table perpendicular to the c axis (parallel to the side of the crystal) and produce a color pie made with four slices of color.  Two of them from the c axis and two from the a/b axis.  I have also cut down the crystal so that I can make reasonably emerald cut that is oriented with either the c axis in the ends or the a/b axis in the ends, or even a square cut.  Showing both dichroic colors can make an interesting gemstone.

8,  Short stocky crystal section that have a closed c axis.

There is really very little to do with type of rough, but I have found that if the c axis is at least useful under stronger day light you can make a interesting stone.  I cut a round with its table parallel to the c axis, like the rough had a moderate c axis tone value.  Under moderate to low light conditions two sections of the cut gemstone will appear dark, but the a/b axis should appear rather like an eye (if it is light enough for this way of cutting to be useful.)  When the level of lighting increases the sides of the eye will begin to be a blend of the c axis color and the a/b color.  This can keep the milder a/b axis color from being washed out by the sun.  In essence you have a round that has color and flash in subdued lighting and still comes on strong in bright sunlight.

9,  Multi-colored rough.

Traditionally the bi/tri colors with the distribution down the crystal are cut in an emerald cut.  I like to use regular angles on the ends, but that will cause mixing of the colors and muddy colors.  You can minimize the mixing by using steeper ends.  If one if the colors is in the terminus of the crystal, try putting the color in the pavilion of a round/shield etc. cut with its table cut perpendicular to the c axis.  The color in the pavilion should fill the stone as long as it is close to face up.  If the colors are in layers that are parallel to the c axis  This is unusual, but it can make a nice gemstone with tilting the table showing the individual colors and the mixed colors face up.

10,  Big hunks of semi-facet material.

Semi-facet material should be good enough to produce small clean gemstones, but I don’t usually find that to be the case or the most useful way to handle the rough.  I go for color while minimizing  the impact of the inclusion/flaws on the finished gemstone.  I like to get bigger pieces of rough, may be 20 carats and above to give me room to saw and grind out the best sections, out of usually pretty included/broken material.  I do not buy pieces that do not show areas of good transparency.  I enjoy accepting the challenge of this kind of rough and it is certainly a gamble, but my collection would not be, what it is color wise, without taking the risk.

 

Bruce