Testing, testing, 1-2, 1-2

One of the first things I’ve dug out to assess ready for sale is a batch of garnet rough from Zambia, acquired from a friend who visited the mines in Sangu in the 90’s. I didn’t know if the quality was much good, and being a relative newcomer to faceting and gemstones (I’m mostly a mineral and fossil collector), I wanted to get a feel for the material before offering it up for sale.

I took a handful of stones (132 stones, ~188g), washed and lightly oiled them to assist seeing inside the stone and visually assessed (2.5x loupe) each one into 4 piles;
AA = Zero flaws
A = Minor flaws, leaving most of the stone clear
B = flawed such that up to half the stone was unusable, and
D = stones that had cracks or internal features like inclusions, ‘fogging’ or negative crystals, extensive enough that it would be difficult to cut a good size &/or quality gem.

What surprised me is that when I photographed them, I noticed I couldn’t really tell the difference visually between the flawless stones and the unusable ones. Have a look. Can you tell? Don’t be fooled by the texture of the LED light panel either: except for large cracks, those stones all look clear, even in person. It’s only under close inspection that you can see the internal features.

This exercise was to help me price and market these gems. What I found is that it’s nearly impossible to show your stones are good quality with just images. So I’m planning on falling back on good after sales service, and a generous return policy. If I’m lucky, once word gets around, it’ll all work out OK. I’m not just in this for the money, everything goes back into high-grading my collection.

I then sorted them by weight to get a rough feel for the size distribution.

* This stone, although big, is fairly flat – it would cut several (4?) small stones, but probably not a single large stone. There is the occasional large stone in this material, though.
^ smallest stones were still larger than 0.5g.

It’s remarkably consistent. Average size is 1.4 g (7 ct) per stone. 80% of the material is between 6 and 10 carats, regardless of grade. If I discard material below 1g and flawed, 82% of the material is cuttable. Based on slicing and dicing the data, and being conservative with my estimates (1g rough = 1 ct cut) it looks like you could expect to get 40 cut stones @ 0.5 – 1 ct, 60 between 1 and 2 ct and 6 stones greater than 2 ct from 132 stones/188g. That’s about a 13% conversion rate rough -> cut, or 63% regular expectations…