Gemstone cut - experts please correct any errors.

[strmrdr]

I should have really called this gemstone color and cut but the I wasnt planning on writing a book.

Before you can get into cut on gemstones there are a few things that need to be explained first.
Some gemstones are just cut to get some shape to the rough so they can be sold with not much attention paid too much else except retaining weight.

The next thing is that gemstones are all about color.
The closer the color is to what is considered the ideal the more expensive the gem.
If that is achieved without any enhancement then the value goes up even more.

There are 2 important parts when it comes to gemstone color.
The strength of the primary color and its relation to the secondary colors is the first.
Examples of primary colors would be red in rubies and blue in sapphires.
A sapphire that has a strong primary red color and weak or no other colors would be a top class ruby color wise.
A sapphire with strong red primary and strong green secondary would be a yellow sapphire.
Remember making custom colors with crayons or paint in art class the same principle applies. When you mix the colors a new color is created the more of one color you used the closer it would be to that color. Add more of the second color and the color changes more.

The second part is saturation or how much color is in the gem.
A gem could be top color but weakly saturated and the color would appear washed out and nasty.
Think of it this way low saturation would be watered down watercolor paint on a piece of paper.
While high saturation would be full strength oil paint on the same paper.

A sapphire that has a strong primary red color and weak secondary colors and is highly saturated would make for a very expensive ruby.

Now your asking what does that long-winded mind numbing stuff have to do with cut.

A good cut gemstone is cut in a way that enhances the color and or saturation present.
For example:
A light colored sapphire with med saturation might be cut deep to increase the appearance of the color in the finished gem,
Remember that gems show color by returning the color of light that the gem is to your eyes and blocking or filtering out the other colors.
A deeper gem uses the longer path to filter the light more returning better colored light at the expense of some brightness,.

On the other hand a darker than optimal sapphire with med saturation might be cut shallow too keep the light return up and appear lighter in color.



It is the same for saturation:
Decent color low saturation = cut deep to color the light more
Decent color and high saturation = cut shallower to keep the light return up.
The ideal gemstone would have high primary color, low secondary colors, high saturation and be cut somewhat shallow and cost a ton of money :}


In some gemstones inclusions can have a large effect on how the light is returned also so we can really modify the last one to read:
The ideal gemstone would have high primary color, low secondary colors, high saturation and be cut somewhat shallow, and not have a lot of inclusions and cost several tons of money :}

There are some other issues with color and cut that are more than I want to get into right now such as zoneing, windows and enhancements.

 

[strmrdr]

Windows:
Windows are when you can see thru a gemstone instead of it returning light to you.
Some gemstones are more prone to this than others.
Low saturation tends to increase the odds of this happening.
Good cutting can eliminate it for the most part but there might be some angles that a window is aparent in even the best cut stones.

 

[Michael_E]

strmrdr,
Windowing is related to two things only and color saturation is not one of them. They are:
1. The angles that both the crown and pavilion are cut at. These angles are pretty much the same for diamond as they are for colored stones. The crown angles have more leeway and can be cut down to very shallow angles for dark materials. I've even seen dished crowns that didn't look too bad.

2. The amount that a stone is tilted when viewing it. The higher the refractive index of the material, the farther that it can be tilted before it windows significantly for any given facet design. Any stone will show a window when viewed at an angle. Some designs like barions are tremendous when viewed face up, but the side angles can be so steep that they show a window out the side with very little tilt.

strmrdr, you're really getting into this. You need to get a faceting machine and start cutting stones. You'd probably like it a lot!

 

[strmrdr]

Thank you for the correction.
Just goes to prove that I have a lot to learn yet.
Your explaination is great :}

Unfortunately I am better with my mind than I am with my hands.
While earning my EET degree I had a ton of problems with surface mount soldering and the precision needed for gem cutting has to be much greater.
I would love to try it but know my limitations.

Im an information hound and when something strikes my fancy I try to learn as much as possible as quickly as possible about it from as many angles as possible.

I have been studying the cutting diagrams here:
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To get an idea of what is involved.
There are a ton of them I would love to see the finished gem for.

For example this one here would look awesome in a bright red material or even bright orange.
click

this one also:
click