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Rough Sapphire evaluation

What percentage of rough sapphire is good enough to cut into good to excellent quality gems.something that is saleable.
I am trying to evaluate how much I should pay for it.

Well that is a pretty broad question, firstly you may know that when a gemstone is cut from rough you normally would lose 2/3rds of the stone. unless it is in a perfect shape to cut to the similar shape it is already. once again depending on if the gem is heat treated or not this on todays market is another major factor with good quality untreated gemstone bringing premium price. so if you are lucky a 3 to 4 carat gem should yield at least a carat. anything under a carat is starting not to be attractive to buyers because it is less than a carat. similarly if a gemstone is of top quality and in the 3 to 5 carat range then it is very much sought after, again depending on colour clarity cut etc. if you are not experienced at looking at rough sapphire for cutting there is a lot of things that can go wrong, for instance, silk in a untreated gem which usually shows up more after cutting, in many cases cracks and flaws in a sapphire are sometimes very hard to distinguish and when cutting you think you have a nice gem and all of a sudden there is a crack just appearing that you didn’t see beforehand. Also sapphires can look great in the rough but if not cut properly depending on how dark the gem is and if it is not orientated properly you can end up with a dull boring gemstone. good luck

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I agree with everything SydP says, though I think you’re being a bit generous on the cutting loss, I tend to tell people around 80% of the stone is lost…anyway;

Buying Sapphire rough, I never buy sight unseen, if you can’t see colour without artificial light you can virtually guarantee the stone will cut dark.

Always have a quality 10X loupe and a narrow beam light to study the stone with the loupe, don’t back light, cross light as it’s more likely to show cracks and internal fissures. Online vendors know this which is why they backlight stones.

Check weights and totally disregard any little plastic cards telling you it’s this or that, they’re all a stitch up.

Price… so many variables, ‘3Cs and an S’ Colour, Clarity and Carat, finally Source.

For pricing you can also work backwards, finished weight @20% or rough weight then sale price, factor in cutting costs; native cut in the orient or precision cut in the US or Aus or where ever you wish, remember the bigger the stone the longer it takes to cut. Your margin and then what happens if the stone develops a stress fracture during cutting, could be a right-off or a couple of tiny stones as a recovery.

Recently a client brought over a jar of Sapphires, around 4-500 stones, once I’d separated the Zircons, topaz and other bits and pieces that were thought to be Sapphires, what was left produced around 10 cutters and some of those may not cut once I window the stones to check inside. It can be a gamble… good luck.

I agree and not worried about the yield.I am also certain that they are all sapphires.
I am ok with 20% yield as well.
I would like to know if i have 1000 gms of rough sapphire from sri lanka how many of those will
yield sapphires with at least average quality.
Is it possible to cut 1 gemstone from each rock or are there many rough rocks which wont yield any sapphire

Hi I cannot speak on Sri Lankan sapphire yield, but when I was hand digging sapphire in Qld Australia, we would generally work on 1 cutter or reasonable stone out of 10 sapphires found. and don’t think that every rough piece of corundum will cut a star as that is not factual either. thanks

Depends entirely on the integrity of your supplier I’m afraid.

But, as its not legal to export rough stones from Sri Lanka, if you are buying such material overseas, then that integrity must be questioned immediately.

It depends on the rough you have, It could be from Sri lanka , Australia or Montana , If you have cab grade Stones you will get pretty lousy faceted stones.

You need to show the parcel to an experienced cutter to get an evaluation , Photos are not good enough evaluate a parcel. ( My opinion )