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 Post subject: Ruby transparency
PostPosted: Sat Sep 22, 2018 12:07 pm 
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Hi,
My second post on rubies ..one might tell I am fascinated by this stone;)
I refer to the criteria of transparency . How objectively do we measure transparency on a ruby? Is it not that a thiner ruby would likely be more transparent than a thicker one?So a bigger ruby would , with the same local crystal clarity of a smaller one , qualify for a lower transparency grade ?
Thanks!


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 Post subject: Re: Ruby transparency
PostPosted: Sat Sep 22, 2018 1:38 pm 
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Joined: Sun Oct 16, 2005 12:22 pm
Posts: 19172
Location: San Francisco
Hi Callie and welcome.
I moved your posts to the colored stone area. More appropriate than chats.
How does one grade quality of a ruby?
Transparency is only one criteria.
If I may, I'm going to quote Richard Hughes, the world's authority on corundum, IMO.
http://www.lotusgemology.com/index.php/ ... isseurship

Image

Dick Hughes wrote:
Seeing red

What do I look for in ruby?
Bright is first and foremost. Can’t stand the dull or dark stuff. Not for me the burgundy reds typical of the Thai/Cambodian border. When I fill my tank, I want gasoline that burns.
Color

With ruby, the intensity of the red color is the primary factor in determining value. The ideal stone displays an intense, rich crimson without being too light or too dark. Stones which are too dark and garnety in appearance, or too light in color, are less highly valued. The finest rubies display a color similar to that of a red traffic light.

There is a tendency for the market to favor stones of the intense red-red color. Certainly the highest prices are paid for these. But do not overlook the slightly less intense shades. Such gems have a brightness missing in their more saturate brethren and often look better in the low lighting that one typically wears fine jewelry. Like beautiful women, rubies come in many shades, the preference for which is a matter of personal taste.

Clarity

Clarity is ruby’s Achilles heel. Red corundum is common. Ruby is incredibly scarce. The key difference is clarity.

In terms of clarity, ruby tends to be far more heavily included than sapphire. While the general rule is to look for stones that are eye-clean, i.e., with no inclusions visible to the unaided eye, extremely fine silk distributed lightly throughout the stone can actually enhance the beauty of some rubies.

For star rubies, a certain amount of silk is necessary to create the star effect, but too much desaturates the color, making it appear grayish. This is undesirable.

Cut

In the market, rubies (and sapphires) are found in a variety of shapes and cutting styles. There is a definite hierarchy. Faceted stones are more valuable than cabochons and cabs are more valuable than beads. Carvings are the least valuable. The reason has to do with clarity. The cleanest rough will be faceted, that not clean enough to facet gets cabbed, that not clean enough to cab gets made into beads and carvings.

With faceted rubies, ovals and cushions are most common, but rounds are also seen, as are other shapes, such as the heart or emerald cut. Slight premiums are paid for round stones, while slight discounts apply for pears and marquises. This is because the shape of the rough typically determines what shape will produce the biggest piece.

Stones that are overly deep or shallow should generally be avoided, as they will lack in brilliance. However one must be more generous in judging a gem as the quality of the material goes up.
Cabochon-cut rubies are common, but fine cabs are rare, indeed. This cut is used for star stones, or those not clean enough to facet. The best cabochons are reasonably transparent, with nice smooth domes and good symmetry. Avoid stones with too much excess weight below the girdle, unless they are priced accordingly.


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 Post subject: Re: Ruby transparency
PostPosted: Mon Sep 24, 2018 4:12 pm 
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Hi,
I have got a reply from ssef on this topic, so I though I would share for the benefit of us all:

the thickness of a stone is not taken into account when judging the transparency because the transparency applies to the full stone itself. Either you can see through the stone (transparent) or not (semi-transparent, translucent, sub-translucent or opaque).


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