Colored gem cuts bottom-heavy?

[raddygast]

Having looked at a number of rings in various places and online (when there are on-hand pics posted) I''ve determined that for the size of my girl''s finger anything over 1-1.25 carats is going to have a dramatic presence, and anything larger will just look off.

The only problem is, diamond cutting seems super standardized (round brilliant ideal, etc). I''ve seen a number of round cut colored gems in the 1.25 ct range and they look FAR FAR smaller, because the weight of the stone is bottom heavy. It''s sort of irritating but I understand it''s necessary to achieve various levels of brilliance and color saturation, which in diamonds is a non-issue (well the saturation is).

Anyone have any suggestions? I really wish that 1 - 1.25 cts in a round cut would actually look as substantial as a round brilliant diamond of the same weight. I''m mainly looking at sapphires and spinels. With spinels perhaps it isn''t the biggest deal (because they aren''t that expensive yet...) but maybe with the finely colored ones I will still be limited in what I can afford. Are there any cuts that seem to maximize face-up size?

 

[Mayacamas]

I am going to try to answer your question- although I am not an expert. Diamonds are catagory I gems- and so they should not be included, and there are repeatable mathmatical models of ideal cutting. Sapphires, and rubies are catagory II stones, and have some inclusions in them and so there are not really repeatable models to follow- they are cut to different proportions so as to maximize the unique characteristics of that one stone, unlike diamonds. Part of this is due to the behavior of light as it travels through a colored stone- and so there needs to be a deeper pavillion for the stone so as to "read" darker, and because light doesnt reflect back in the same manner the stone needs to be cut deeper to exhibit brilliance.




Some stones are cut , however, super deep just to increase their carat weight for purchase. If you check out sites such as Cherry Picked ( which I see you are familiar with), Pala gems, and ajsgems, you will find that the proportions are distinctly different than diamonds- which means you have to be very picky about each stone- you cant just buy a cetificate.




The ring I have pictured has an awesome sapphire in it , but notice that its pavillion is deep- part of this is to give the depth of color to the stone, and part is to increase the amount I paid per carat!




The benefit of places like Cherry Picked and Pala is that they are reputable, knowledgeable and sell what they say you are selling. You pay a lot for this knowledge, but then again, if you are buying something nice, you will probably be paying alot anyway.

I wish you the best- nothing is more satisfying than having a great colored stone- its like having rare and unique art. Diamonds, are after all, kinda common relative to colored stones.




Not that they are not pretty, too!

 

[strmrdr]

sapphire is heavier for any given volume of material than diamond.

Its specific gravity is higher.

Specific gravity is the number of times heavier a gemstone of any volume is than an equal volume of water; in other words, it is the ratio of the density of the gemstone to the density of water

What that means lets say you take a diamond ball and a sapphire ball both 1mm in diameter they would be the same size but the diamond one would be lighter.

Corundum (hardness: 9 Mohs)
Specific gravity: 3.96-4.05

Diamond (hardness: 10 Mohs)
Specific gravity: 3.51

Add that to the different cutting styles and at times it can take a sapphire over twice as heavy to face up the same size as a diamond.

 

[strmrdr]

for example:
http://www.diamondexpert.com/

The Sapphire linked above is 3.96x4.02x3.33mm and weighs .483ct
For comparison a typical .23ct diamond will be around 4mm

 

[Michael_E]

raddygast,
Most of the finest colored sapphires that you will see have been cut in Thailand and are cut to maximize the weight retained from the rough stone. if the stone is a little deep then you should be thankful as that is far better than a stone that has been cut too shallowly. I've attached a picture from an e-bay auction of a ruby that has been cut very shallowly and which, although attractive, will never show much life, face up. The reason is that the angles at the bottom of the pavilion are too shallow to reflect light and so all of the light hitting those facets goes right on through and all you've got is a pretty red window. When you are looking for a sapphire, you should be looking for a stone that is in the 2 to 2 1/2 carat range and which is cut a little deeply. If you don't like the cut you can always have it re-cut to a brighter look and you won't lose any size across the diameter. If you want a shallow stone re-cut you are forced to reduce the diameter significantly to eliminate the window and get a bright stone.

Your last question, "Are there any cuts that seem to maximize face-up size?", certainly, but it will require that you either have a stone cut from rough or have a stone that is already cut, be re-cut to your specs. IN the sizes that you are talking about, the cutting costs are not very high and you can often find some decent rough on E-bay or through some of the Internet rough vendors that will cut to your size specs, but it will not be that really fine neon blue material. If you like decent, darker royal blue material, still good blue, not inky, but darker, then this is a good route to take.

 

[bar01]

I am no expert either - but according to one of the books I read (by Renee Newman)- say something a depth the range of 65-80% depth is desirable.