This post is centered on a stone that I just finish from a piece of rough I receive a couple of months ago from Africa. The rough weighed 6.5 carats and had both inclusions and two ugly iron areas that projected into the rather flat and completely water worn pebble. The first thing I did, after looking the rough over, was to grind a nascent table. It is important that the grinding be deep enough, so that only a small amount of additional grinding will needed to be done, when the crown is cut on this piece, because the rough is quite thin. I don’t grind a preform to remove the maximum material or produce the perfect shape. I grind to facilitate centering. In this case two areas of iron stain remained after the preforming, in diagonal corners of the preform. I dopped the preform with a smaller dop stick than usual because I knew that I would be cutting the preform down to get rid of the iron. I tolerate many problems with cuprian tourmaline, but not iron stains.
I made a preliminary cut of the pavilion and found the preform was well positioned to be reduced in size with a reasonably hope of completely eliminating the iron. I put my well worn 3000 grit lap on and carefully cut the pavilion again, after I had narrowed the width enough to get a girdle cleared of the iron. I was being both delicate and careful because the stone is included and there is very little depth to spare. The polishing goes very well and I transfer the stone.
When I transfer a stone I can get some rotation depending on the dop stick. I also level my faceting jig on the table, each time I start cutting a stone and when I transfer a stone. After grinding the wax off and positioning the stone level and making some preliminary cuts to see the the preform has not rotated too much, I am ready to cut the crown. I now have a clear view of both the residual flaws in the stone and the iron areas. This is going to be a close cut. I decide on a step cut crown because the iron areas will be under facets and they will be easier to remove without lowering the crown. The darker iron area turns out to be a growth tube filled with orangish brown material. It seems reasonably stable and I cut the first step facet about half way to the girdle. I am making the first round of facets next to the girdle thirty eight degrees, which is exactly parallel to the growth tube, this is going to work! I continue around the oval cutting the facets about half way to the girdle. When I reach the other iron spot it goes thud and I have breakage. I look and I still have enough stone so I go on. After completing the rough cut, I put on my well worn 3000 grit lap and take her down. The stone is not completely oriented properly and I do make one radial adjustment, but I don’t have room for more. I will have to polish in the facets when I am done cutting. The stable growth tube disappears with little to spare and when I get to the other iron spot I get a big clunk and I figure that the stone is done. Well it appears that breakage left a trench, with a round cross section. It must have held something like a tube and it is not too deep, because it is exactly at the same angle I am cutting. So I take the first row of facets down to a thin even girdle and complete a row of thirty degree steps. They are not all parallel and again I will be polishing in the meets. The table does have to come in a bit and I remove some surface problems that I missed before. The final polish of even the table is easy until I find the c axis. This stone is not dichroic in the least and I get a little undercutting when I polish the facets perpendicular to the c axis. You will never notice it by eye.
So now it sits in a storage box. It is bright, but it is still moderately included. The best part is that I can not see any indications of iron or the breakage area next to the girdle. Also none of the inclusions are flashers or obnoxious. The stone measures 7.7mm by 5mm and weighs .70 carats. Its color is a better blue than when I started because of the removal of the yellowish iron areas.
So another adventure with cutting flawed material yields a gem that must be rated like emerald and their “garden” with only 9.5% of the original weight retained. Such is the adventure, with the cuprian rough I can still get. (2013)
Bruce
I will post a picture when Jeff makes one.
