Color and Light

[empress]

We’ve been talking about color and light. Color shift is mentioned here quite often. I would like to examine how the two relate. The gem does not actually shift color – it’s chemical composition doesn’t change – it’s the light that hits the gem and is returned to our eyes that changes.

Originally, one had only sunlight by which to see and judge a gem. Then sunlight and fluid or fat lamps. Then gaslight was added. Then incandescent and fluorescent. Now we have LCD, LED and new generations of light coming along.

So, if we hold by the notion that some promote that gems “should” hold their color in current lights – assuming this means incandescent and fluorescent as well as sunlight – what happens to the “value” of those stones as those sources are fazed out of use (incandescent for sure) and the colors appear different in the new lighting sources.

Does this crash the market? Do we start with new values?

Or does it really rely on the color of gems in sunlight?

 

[PrecisionGem]

Good point. These new light bulbs for the most part make everything, including people and gemstones look horrid.

Most professionals judge the color of a stone in natural sunlight, but never direct sun. Typically one will take the stone outdoors, and either in indirect sun, or with you back to the sun and your body blocking the direct sun view the stone. I've never seen a professional hold the stone directly in the bright sun. Most times a potential buyer tries to view the stone in a variety of light too.

 

[ooo~Shiney!]

Hi, I am really just a learner myself, but I have been pretty fascinated by this topic...

I will be interested to hear what others have to say

 

[deorwine]

The really crazy thing is that (at least for me) a gemstone can also look different in sunlight in different geographical areas. I have a sapphire that I love that's a bright blue color in the blazing bright sunlight in CA, and when I was on a trip to the East Coast recently (where it was much more hazy, though still sunny) I noticed the sapphire looked noticeably less saturated and even a very very slightly bit more purple...

But yeah. It weirds me out how different things look in different lights. Even a certain type, like fluorescents... my work fluorescents are very harsh, and very few gemstones look good under them (the ones that do I prize like anything!) -- but when I go shopping, the same stones that look like crap at work look quite nice under the local TJ's fluorescents.

 

[Pandora II]

http://www.jckonline.com/article/281985-The_Best_Light_for_Buying_and_Selling_Gems.php

Interesting read.

Gene - and any other cutters...

When you buy rough or cut stones for your inventory do you take into account the light at your hometown compared with that where you are buying. Or the latitude of most of your customers?

Can you think well, that looks a nice periwinkle blue here in Thailand but it's going to look steely blue when I get it to NYC, but then if I flog it to someone down in California it's going to look super-dooper again?

I wrote a whole load on this in Brightice's thread on red spinel.

 

[kenny]

Let's not forget to factor in the powerful influence of the brain, on what we think we see.
Even before electricity light varied in strength AND color.

I used to work in a lab that had to have VERY yellow lights because the chemicals used there didn't react to it.
When you first walk in you are smacked in the head with the strong yellow.
Everything lookd VERY yellow, even our white smocks.
After a while you adjust.
You could still tell colors apart but the yellowish cast to everything was no longer noticeable.
When you walked out into regular florescent light "the purple" smacked you in the head.
Suddenly our white smocks looked purple, the opposite of yellow.
Of course they weren't purple, but the brain/eye system was tuned to function in a yellow environment, and that "tuning" takes a while to wear off.
If a white smock can appear to change color perhaps a gem could too.

Daylight, sunny, shady on a cloudy day vs. shady on a sunny day, morning sun, mid day sun, evening sun, sun breaking through dark storm clouds, fluorescent and tungsten are actually all lights with very very different "color".
Our brains white balance for varying light sources without our noticing.
This marvelous ability of the brain is to blame for why white balancing a camera is so hard to comprehend for many.
People may think, "doesn't the camera just do what my eyes do?" No, because it is not part of such a sophisticated eye/brain system.

Let's take some green object (it doesn't even have to be a gem) and move it to different 3 environments, sunlight, florescent and tungsten.
I'm curious if the person would perceive that same object as a slightly different green after their brain/eyes have adjusted to the light.
I wonder whether this explains some of the change reported when gems are viewed in different light sources.

I'm not saying gems do not change color in different light.
I'm just wondering whether all or part of it is the result of the hue compensation that our brains dial in when the light source changes.

 

[Pandora II]

Nail on the head Kenny!

One of the things that they endlessly tell us on my course is that colour is subjective and everyone will see things slightly differently.

So if 6 of us are looking at a red stone, two might see it as an orange-red, another 2 as a pink-red and the others as a red-red. None of the answers are wrong as it is simply how it appears to each individual.

 

[PrecisionGem]

http://www.jckonline.com/article/281985-The_Best_Light_for_Buying_and_Selling_Gems.php

Interesting read.

Gene - and any other cutters...

When you buy rough or cut stones for your inventory do you take into account the light at your hometown compared with that where you are buying. Or the latitude of most of your customers?

Can you think well, that looks a nice periwinkle blue here in Thailand but it's going to look steely blue when I get it to NYC, but then if I flog it to someone down in California it's going to look super-dooper again?

I wrote a whole load on this in Brightice's thread on red spinel.

I think the time of day, and the amount of cloud cover have more to play with the color than the latitude and longitude. A very smoggy day in LA isn't going to be the same as a clear day in LA. When buying rough I always want to see the stone in 3 different light sources; incandescent, florescent and daylight. Sometimes this isn't always possible, but it's always desirable.

 

[kenny]

Nail on the head Kenny!

One of the things that they endlessly tell us on my course is that colour is subjective and everyone will see things slightly differently.

So if 6 of us are looking at a red stone, two might see it as an orange-red, another 2 as a pink-red and the others as a red-red. None of the answers are wrong as it is simply how it appears to each individual.

Also there is the lack of controlled consistent color training.
Being taught that this apple is red and that banana is yellow and that lime is green is not a sharp enough pencil.

We won't be there till all the young children of the world are shown calibrated chips of Pantone colors and taught their names and get tested again and again till they got perfect scores.
Of course this will never happen.

Even such training would not address people's variations in color sensitivity and the hue discrimination "holes" that are much more subtle than what we've labeled color blindness.

A couple months ago someone posted a color discrimination test, and most of us were surprised we didn't get better if not perfect scores.

 

[zeolite]

if we hold by the notion that some promote that gems “should” hold their color in current lights – assuming this means incandescent and fluorescent as well as sunlight

Gems appear different in different light sources for many reasons. The characteristic of the light source is one.

Daylight and incandescent (ordinary light bulbs) are both continuous in spectrum. If you measured daylight with a spectro-photometer, you would see continuous wavelengths of light, from red to violet, with no color (wavelengths) missing (I had the exclusive use of a $37,000 spectro-photometer for about 20 years). But the daylight would be relatively strong in blue and weaker in red. If you measured the incandescent light, it would also show continuous wavelengths, but would be stronger in red than blue.

 

[zeolite]

Fluorescent bulbs do not have a continuous spectrum. Some wavelengths are completely missing. The picture below shows the spectrum of light from a florescent lamp, that has been spread with a diffraction grating. You can see some missing wavelengths. Charts that show the fluorescent spectrum with broad color bars are misleading. Some graphs indicate strong red, which is not really true. No fluorescent bulb shows a strong red longer than about 635 nm, which is orangy-red. True intense red is 660 nm or longer. For this reason, rubies or red spinels will looks very weak and sick under any fluorescent bulb.

 

[zeolite]

The trace elements in that specific gem crystal structure, that absorb the incoming light, is another reason for not holding their color. If you look at a continuous light source with a spectrometer, you will the light spread out in a broad band from red to violet. If you place a gemstone between the light source and the spectrometer, you will see that the gem may filter out wide bands of color. A ruby for example, will block nearly all blue light.

So considering differences in light sources and differences of different gem species absorbing specific wavelengths, it is a bit unreasonable to expect them to hold the same color. Hope this isn’t too pendantic.

 

[T L]

I don't think it's realistic to expect a gem to hold it's color in any light source, although I have a pink tourmaline that really holds it in every lighting I have been in, fluorescent, incandescent, sunlight, etc. . . and I posted photos here to show it. I think the most important thing is that a gem should maintain a nice saturation of color in various light sources. I've seen so many gems that look magnificent in one light source, only to lose a great deal of saturation in their color shift to another light source. Also, I know red spinels tend to lose saturation in fluorescent light as Mr. Zeolite (long time, no hear friend!! ) stated, but some hold their saturation better than others. You definitely don't want a red spinel to go go muddy orange in fluorescent light, while be hot saturated pink or red in sunlight. That's always been my issue with color shifts, and what I commonly warn others about.

 

[PrecisionGem]

Actually, if you look at sunlight through a spectrometer, you will see a series of lines of absorption. These are called Fraunhofer lines. Sunlight as it reaches the earth is not a pure continuous spectrum. We actually use one of these lines to calibrate the hand held spectra scope.

 

[Arcadian]

most of my stones change colors, thankfully to something I really like. Some stones of course are nearly impossible photograph correctly (my newest spess is like that) I guess I really don't expect a stone to hold a color in every light, as long as the color it changes to is something I actually like. Stones that stay the same all the time, to me, thats kinda boring.


However, my tastes in gems is quite pedestrian, and I'm more forgiving of a stones natural tendencies.

-A

 

[deorwine]

I think the time of day, and the amount of cloud cover have more to play with the color than the latitude and longitude. A very smoggy day in LA isn't going to be the same as a clear day in LA.

Yeah, with my traveling experience I think it had a lot more to do with the relative moisture content of the air in MD vs. CA than with the relative lat/long. But wow, it did have a substantial effect. Even my traveling companion, who does not do gemstones at all, remarked on the difference in the quality of the sunlight, even though it was sunny both in MD and CA. And I think the moisture/haze in MD was typical, not more or less than usual. Made me happy for several reasons that I live in CA

TL, I like what you say about saturation. I need to remember that. I keep discarding gems because I don't like the way they shift in this light or that... where I really should learn to love all colors. (My baby daughter is helping with that; her favorite colors are yellow and orange, which I used to dislike, but now I have to like for her sake! Gotta source a fanta spessartite for the kid when she gets older...)

 

[mastercutgems]

I know when buying rough it is more tricky than buying a cut gem as you do not have the clear picture of what the gem will look like faceted; it is more one dimensional than 3 dimensional when you look at rough opposed to a finished faceted gem; in other words with the finished gem; it is what it is.... In a piece of rough it is what it could possibly be after you cut it .

Plus you get to look at all the other diversities such as dichroic, trichroic, etc. as that will throw a monkey wrench in on the scheme of things as it makes the mind tick as to how you are going to orient it and what color wheel will you use to figure out what combination of colors will do what and will it make a lovely blended color or a nasty muted brown thingy???

I try to go by some basic rules; the white paper test of course in subdued or shielded sunlight; depth to width ratio, and clarity. If the color is pleasing in all of those situations; and it does not have a color combination that stinks??? it still is a gamble but not as much as if it only passes 2 of the 3...

That is just some of my ways; I am sure most cutters will have their own way they like to view rough; and rules they use to weed out the less desirable ones...

Many times you will not have the option of multi-various lighting conditions; but I always fall back to the sun when i need the "best" light source.

Good information and a great topic as so many view their gems in different lights; home, work, etc... It would be nice for them to look great in every light; but most do not and the ones that do; will normally fetch a premium as they are a premium color in all or most lighting situations.

Fun topic

Most respectfully;

Dana