transparency

[diamondsrock]

I was wondering why transparency is not listed as a separate factor in grading diamonds. I would assume diamonds can have varying degrees of transparency. Some seem crystal clear like water and mirrors and others seem kind of dull, even after cleaned. Of course some look dull because they''re dirty or highly included, too. Or not cut well I guess. When shopping for a diamond, this would be an important factor for me yet it''s not listed anywhere. Are the variances so small that they''re not worth noting? If you go with a high clarity stone does that guarantee the stone will be highly transparent also? Just curious. Thanks!

 

[JohnQuixote]

Hi DR.

''Transparency'' is the ability of a substance to transmit light. Diamond’s refractive index (2.42) and dispersion (0.044) are constants. The term transparency as it relates to diamond can be primarily tied into the color grade. A perfect diamond crystal has only carbon atoms. Such a diamond is colorless. The presence of nitrogen is responsible for color, and the amount of nitrogen present when the diamond was formed underground determines the degree of yellow tint it will show. A colorless diamond, like a clear window, allows more light to pass through, compared to less transparent diamonds (those with more color).

Clarity issues (clouds, etc.) and ill performance due to poor cut may influence ‘transparency’ as a viewer interprets it, but the color grade is primarily where this aspect is covered.

 

[Spear]

A diamond''s certificate usually has a grade for polish.
Polish marks, polish lines, nicks and scratches effect a stones transparency.
And transparency is a key component to brilliance.
Polish grades are as follows: poor, fair, good, very good, excellent.
Polish charateristics are essentially blemishes.

How I understand it, is that inclusions largely affect the clarity grade while blemishes largely affect the cut grade under the term polish.

I am not an expert, so please return to this thread for additional replies.

 

[denverappraiser]

Transparency can be a tricky thing to measure. Although clarity can be a problem for the light performance, it isn’t really an optics issue for grades above about SI1. Color will change the character of the light as it passes through the stone and a certain amount is absorbed in the process but this isn’t all that big an effect on the brilliance. Most of what you’re seeing that makes one stone look dead while a superficially similar stone is not, is based on the cutting (including polishing), the cleaning and the lighting environment.

Neil Beaty
GG(GIA) ISA NAJA
Independent Appraisals in Denver

 

[Spear]

As Jonh pointed out,
A coulourless diamond is like a clear window.

A coloured diamond would be like a tinted window.
Its harder to see through a tinted window then a colourless window.

A diamond with a lot of blemishes is like a dirty window.
Its harder to see through a dirty window then through a clean window.

 

[diamondsrock]

Thanks for your input. I was really surprised to learn about the color affecting transparency so much. I have an m colored vs2 stone graded by an independent appraiser (gia graduate gemologist). The stone seems to display very good transparency to me, it''s like little mirrors inside. In fact I have gotten comments on how sparkly it is. I have seen some other stones which are higher in color but don''t display the same effect. They seem almost lifeless. I may be shopping for an upgrade in the near future (thanks to hubby

and want to guarantee my next stone (which will be higher in color) will display this same transparency. Following from the color comment, does that mean that fancy yellow diamonds or blue diamonds aren''t transparent? Also, surely going to a higher color doesn''t guarantee transparency, right? I do understand how a colorless transparent stone would reflect more light than a near colorless transparent stone but I really thought cut and clarity would have a higher impact on this than color. So much to learn!!!

 

[JohnQuixote]

Hi DR

The original question was “why isn’t transparency listed as a separate factor?” I was offering input on why there is not a separate transparency grade. I did not mean to imply that diamonds of lower color don’t have transparency or that color has an effect on brilliancy. A well-cut stone of lower color can look wonderfully brilliant.

Robert Shipley used the term 'water' as a quality designation for color and transparency of diamonds, rubies and other stones. In his definition, color and transparency together equal water... Another word that has been used is diaphanity.

Whatever you term it, that quality is reflected (get it?)

in the grading of color & clarity and in cut, which includes finishing details of polish (thanks Spear).

 

[diamondsrock]

ok, I get it. Thanks for the input, John! I think it will just come down to seeing it with my eyes to judge and I won''t be able to see anything on the grading reports for this. Thanks!