Ideal Sapphire /Ruby Depth

[treasurehunter]

Ideal depth for a sapphire. Pavilion percentage , thanks

 

[GregS]

I may be wrong, but there is no ideal depth like you'll find in diamonds, however a depth percentage of 60% or more is usually a good idea.

 

[treasurehunter]

Right I understand that depending on the material for example if its a lighter blue it needs to be cut deeper and a darker stone shallower but if its ideal material that doesn't need to be cut shallow or deep is 60 percent the perfect size.
Also what sort of mm size in 1ct , 2 ct for dimensions

 

[minousbijoux]

I'm surprised that the cutters have not responded to you. Unfortunately, there is no one correct answer. I have seen well cut corundum ranging from probably 55% to 80% depth depending upon the shape, height of crown, etc. I find that I largely go by the look of the stone rather than its dimensions - if there is something off about the stone, like extinction in the center, then I might look to the dimensions to see if there is sufficient depth for a recut. I would tend to generally disagree with your comment about tone dictating the depth of the cut. Given good clarity and saturation, most cutters want to cut to take advantage of the stone's refractive index, which remains the same regardless of tone (lightness/darkness). So regardless of lightness or darkness, the stone should be cut in a similar manner to maximize light reflection; it would just result in a lighter stone in some cases and a darker one in others.

 

[Roger Dery]

I'm surprised that the cutters have not responded to you. Unfortunately, there is no one correct answer. I have seen well cut corundum ranging from probably 55% to 80% depth depending upon the shape, height of crown, etc. I find that I largely go by the look of the stone rather than its dimensions - if there is something off about the stone, like extinction in the center, then I might look to the dimensions to see if there is sufficient depth for a recut. I would tend to generally disagree with your comment about tone dictating the depth of the cut. Given good clarity and saturation, most cutters want to cut to take advantage of the stone's refractive index, which remains the same regardless of tone (lightness/darkness). So regardless of lightness or darkness, the stone should be cut in a similar manner to maximize light reflection; it would just result in a lighter stone in some cases and a darker one in others.

Well, see above, no response necessary! Can take a day off.....

 

[SB621]

Right I understand that depending on the material for example if its a lighter blue it needs to be cut deeper and a darker stone shallower but if its ideal material that doesn't need to be cut shallow or deep is 60 percent the perfect size.
Also what sort of mm size in 1ct , 2 ct for dimensions

Colored stones have a different weight then diamonds. So a 2ct sapphire is lighter (I believe????) then a 2ct diamond. For CS you should completely ignore the carat weight and only go off mm.

However in "diamonds" 2ct round brilliant that is not shallow or deep equals roughly 8mm.

 

[minousbijoux]

Okay, Roger, but now that we've sucked you in (bwah hah hah haaa), I see that the OP also asks about pavilion depth. Do you have rules of the road for ratios between pavilion and crown or anything along those lines? Thank you.

 

[treasurehunter]

Does the level of saturation or tone determine optimal depth ?

 

[pregcurious]

I think Sapphires are more dense; a 2 ct sapphire will be smaller than a 2 ct diamond.

 

[Roger Dery]

Ideal depth for a sapphire. Pavilion percentage , thanks

treasurehunter, there should actually be two questions here:
1- overall depth percentage
Which is what most faceters concern themselves with. In a most general way, depth ratios of over 60% and just over 70% are "normally" acceptable. But, there are several factors including refractive index, design elements and style of facet arrangement, outline, tonal range of existing material, wanting to make the finished gem darker, wanting to make the finished gem lighter, choosing to increase scintillation, choosing to increase dispersion (if it exists), rarity of gem type, rarity of color within gem type, and overall beauty of the gemstone.

2- depth of pavilion only
#1 and #2 are closely related. However, it is possible to facet a crown shallower than the acceptable height ratio, and still have a beautiful gem.

There are always compromises waiting for the experienced cutter. And, most experienced cutters do not live or die by the printed diagram. They go with what works best for any particular piece of gem rough [using their best judgement based on their experience]. Generally, but not always, this is true. Sometimes we are cutting to meet the specs of a client request. And then, again, we are judging what we have in front of us based on experience to the desires of the client.

Hope this is a little bit helpful.

 

[Roger Dery]

Right I understand that depending on the material for example if its a lighter blue it needs to be cut deeper and a darker stone shallower but if its ideal material that doesn't need to be cut shallow or deep is 60 percent the perfect size.
Also what sort of mm size in 1ct , 2 ct for dimensions

Some examples.... and this is only generally speaking:
A well-cut but native cut round Sapphire measuring 6.0 with depth of 4.0 will weigh between 1.10ct and 1.20ct.
In ovals, a 7.0 x 5.0 x 3.6mm will weigh over .90ct and under 1.10ct
In ovals, a 8.0 x 6.0 x 4.4mm will weigh over 1.40ct and under 1.65ct

Regarding the variations in wgt in ovals, sometimes the pavilion will have 3, 4 or 5 tiers of step cuts. So, there will always be a range.

 

[royalstarrynight]

I think Sapphires are more dense; a 2 ct sapphire will be smaller than a 2 ct diamond.

Yes. A carat is a measure of unit. It's like saying 1kg of water is heavier than 1kg of air.

However, higher density would make sapphires face up smaller compared to how diamonds face up. IE 6mm instead of 6.5mm for the same weight.

 

[chrono]

Does the level of saturation or tone determine optimal depth ?

Yes and no. A lapidary will always try to get the best colour and preserve the carat weight at the same time. Sometimes, due to the shape of the rough, he or she has no choice but to select a shallower or deeper design. In general, 60% to 70% is a good middle ground.

Mm size to ct weight for each shape will vary. None of the below are exact but only approximations.
Round: 1 ct = 6 mm, 2 ct = 7.5 mm
Oval: 1 ct = 7 x 5 mm, 2 ct = 9 x 7 mm
Rectangular = 1 ct = 7 x 5 mm, 2 ct = 9 x 7 mm
Pear: 1 ct = 8 x 6 mm, 2 ct = 9.5 x 6.5 mm

 

[minousbijoux]

Ideal depth for a sapphire. Pavilion percentage , thanks

treasurehunter, there should actually be two questions here:
1- overall depth percentage
Which is what most faceters concern themselves with. In a most general way, depth ratios of over 60% and just over 70% are "normally" acceptable. But, there are several factors including refractive index, design elements and style of facet arrangement, outline, tonal range of existing material, wanting to make the finished gem darker, wanting to make the finished gem lighter, choosing to increase scintillation, choosing to increase dispersion (if it exists), rarity of gem type, rarity of color within gem type, and overall beauty of the gemstone.

2- depth of pavilion only
#1 and #2 are closely related. However, it is possible to facet a crown shallower than the acceptable height ratio, and still have a beautiful gem.

There are always compromises waiting for the experienced cutter. And, most experienced cutters do not live or die by the printed diagram. They go with what works best for any particular piece of gem rough [using their best judgement based on their experience]. Generally, but not always, this is true. Sometimes we are cutting to meet the specs of a client request. And then, again, we are judging what we have in front of us based on experience to the desires of the client.

Hope this is a little bit helpful.

I'm not the OP, but as usual, your explanations are comprehensive and helpful in understanding why there is no one size fits all.

 

[treasurehunter]

should you buy a sapphire on a Spread basis and not a Carat weigh basis ? For example will a well cut shallow stone which faces up the same as a deeper stone but weigh less be worth the same or less.If a 1.8 ct faces up the same as a 2ct+ for example.

 

[chrono]

should you buy a sapphire on a Spread basis and not a Carat weigh basis ? For example will a well cut shallow stone which faces up the same as a deeper stone but weigh less be worth the same or less.If a 1.8 ct faces up the same as a 2ct+ for example.

Yes and no. I would buy based on carat weight and spread (if the colour checks out first, of course. ). Worth is a difficult thing to assign a value to because pricing is based on too many different factors:
1. How much the lapidary / vendor purchased it for
2. How quickly the vendor wants to move the stone
3. How much the vendor thinks he/she can sell he stone for

As you know, first and foremost, colour sets the price. Then treatment, carat weight, clarity, cut and whatever other Cs are left. There are price jumps at certain carat weight markers so a 2 carat stone will generally be priced more than a 1.8 carat stone, even if it faces up smaller than the 1.8 carat corundum, if all else is equal. That said, if a stone is well cut, it will not be considered shallow but cut to the right depth.

 

[tangodoc]

Hi, I have a related question. I am looking to make a low-profile ring and want a 1-2 carat oval color change sapphire. What is the least depth I can have without the stone being too windowed? I am looking for a strongly saturated blue to purple stone. Thanks!