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 Post subject: chelsea filter reaction
PostPosted: Thu Dec 11, 2014 1:32 pm 
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Hi, my name is Phil I’m a gem-a passed foundation member, I do not work in the trade but am a keen collector of gemstones/rough as my budget allows, I have recently joined gemologyonline.com. after looking through some of your previous subjects I came across the postings about the Chelsea colour filter, amazed to learn that using it on Prasiolite Quartz if it stays green its natural and if its pinky its heat treated. I checked mine out with three different torches and it stayed green(great result), then I used my zelco flexi long reach torch with high intensity xenon lamp and stone were light pinkish(now I’m confused). I wonder if you could help me out? The site is a great find keep up the good work. kind regards Phil.


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 Post subject: Re: chelsea filter reaction
PostPosted: Thu Dec 11, 2014 6:22 pm 
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Hi
I moved this thread to a more appropriate area. :D


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 Post subject: Re: chelsea filter reaction
PostPosted: Thu Dec 11, 2014 7:22 pm 
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Hi Philip and welcome,
Since you are new Barbra , who is our hostess , did not bark at you with words to the effect that
Chelsea filters are useless.
Filters are one of those things that people wish could help out with gemology but I don't know whether they are very useful. For reasons like your question above.

There ARE some very highly respected gemologists that do use the Chelsea filter.
But lets just look at YOUR experiment. You used two different light sources and got two different contrary results. This means that at least for green quartz the use of the chelsea filter is very sensitive to the source of light. But no one has ever specified the exact light source that should be used. When it was originated in the UK in the twenties or thirties quartz halogen lighting had not even been invented. So the original Chelsea filter was expecting a 2700 to 2900 degrees Kelvin light source.

Your xenon flashlight bubb although battery powered has been engineered to run hot , have a high color temp and burn out quickly like in ten or twenty hours. Therefore you could infer (in the absence of a spectrophotometric measurement ) a color temp of as high as 3400 degrees K.

Since all you changed was the light source this has to be the cause. Which set up do you believe?
I don't know the answer to that. Even when you settle on one light source to use, does that mean you have to take a measurement of your torches battery voltage before each use??

A very very long time ago a geologist in Vienna Professor Dr. Michel patented the Detectoscope which was a filter outfit that involved colored lights and filters in front of the eye that was supposed help with determinative gemology but it did not catch on.

http://www.hakes.com/item.asp?Auction=192&ItemNo=58005

Dr. Hannemann has more recently designed a sets of filters for gemology. I don't know how widely used they are.


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 Post subject: Re: chelsea filter reaction
PostPosted: Thu Dec 11, 2014 9:58 pm 
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Hi Phillip.
Just as a refresher
The Spring 2013 issue of The Journal of Gemmology had an excellent article by Ulrich Henn and Rainer Schultz-Güttler called ‘Review of some current coloured quartz varieties’. For those who don’t have access to this journal, published by the Gemmological Association of Great Britain, this is a short summary to help you distinguish the different varieties:
The Colours of Quartz
Quote:
Image
Uncut amethyst crystal, prasiolite (11,5 ct), rock crystal (20,5 ct), amethyst (2,5 ct), citrine (natural?) (8 ct), citrine and rose quartz rough

In Antoinette Matlins book: Chelsea and Synthetic Emerald Filters Made Easy: The "RIGHT-WAY" Guide to Using Gem Identification Tools
She describes proper usage of the Chelsea as simply viewing a stone with a bright light while looking through the Chelsea Filter.

I've used a MagLite in the past, on those occasions when I've had a Lucille Ball moment and thought it might be a good idea to look at something through a filter. :wink:


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 Post subject: Re: chelsea filter reaction
PostPosted: Thu Dec 11, 2014 11:39 pm 
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G4Lab wrote:
I don't know whether they are very useful. For reasons like your question above.

There seem to be a few usecases for which they are excellent (quick separation of blue topaz and aqua, chrome tourmaline from common green dravite).

G4Lab wrote:
Dr. Hannemann has more recently designed a sets of filters for gemology. I don't know how widely used they are.

I've seen a number of people using them 'in the wild.' They're definitely out there.

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 Post subject: Re: chelsea filter reaction
PostPosted: Thu Dec 11, 2014 11:55 pm 
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Agreed scarodactyl, it we know a parcel of unknowns is either A or B, a filter can be useful.
If we have no idea what the unknowns could be, a filter is useless.
That's why with prasiolite (once it has been positively identified), we know it is A (heated) or B (the result of gamma irradiation), therefore: Filter: Useful. :D


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 Post subject: Re: chelsea filter reaction
PostPosted: Fri Dec 12, 2014 9:21 am 
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thank you for your replies, the flexi light was supplied with my Gem-A course work so I presume its adaquate for tests, when using this and the CCF the green quarts(parsiolite) shows pinky pointing to irradiated quartz, I also except the CCF is very limited, regards Phil


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 Post subject: Re: chelsea filter reaction
PostPosted: Sat Dec 13, 2014 1:01 pm 
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It is doubtful that the fact that the Gem-A supplying the light , constitutes a formal endorsement for using it with the CCF. Although I can see how one might arrive at that conclusion. It probably is as good as anything else.

But the consistency of any battery powered light source whether a FlexiLite or a Mag Lite
or other filament lamp is always going to be a problem. Actually that is an area where LEDs are superior. They vary in brightness but the color temp does not drift much on the fluorescent types (it is likely to on RGB types).


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 Post subject: Re: chelsea filter reaction
PostPosted: Sat Dec 13, 2014 1:15 pm 
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Gene, you may be over thinking this. :wink:


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 Post subject: Re: chelsea filter reaction
PostPosted: Sat Dec 13, 2014 6:19 pm 
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Probably :lol: :lol:
But take a look at a graph showing the spectral curves of tungsten lights at different color temperatures from say 2500 to 3400 degrees K and the light going INTO the stone is so different that it can effect the results.

I will see if I can find the graph I have in mind online. The one I am thinking of appeared in the "Light Sources" chapter of the Handbook of the Optical Society of America.


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 Post subject: Re: chelsea filter reaction
PostPosted: Sun Dec 14, 2014 9:30 am 
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hi, phil again, I agree with G4lab, I try to look into the reasons for the difference of what I though would be a simple and quick test green quartz heated or irradiated, the CCF is meant to be illuminate with strong tungsten light source which will fall into the degree k G4lab reported, the other torches I used fall outside of this which is why I observed the green colour and no change,??. Barbra thanks, I think my CCF will only be used for when its separating the blue stones or chrome tourmaline. thanks to everyone for your help from this amateur.


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 Post subject: Re: chelsea filter reaction
PostPosted: Sun Dec 14, 2014 2:43 pm 
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Just as a sidebar. Not all Cr tourmaline is valuable.
Sophisticated gem buyers buy beauty, not chemistry. 8)


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 Post subject: Re: chelsea filter reaction
PostPosted: Sun Dec 14, 2014 9:52 pm 
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Barbra Voltaire wrote:
Sophisticated gem buyers buy beauty, not chemistry. 8)

(Chemistry matters too, though! It depends on what kind of a customer or collector they are.)

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 Post subject: Re: chelsea filter reaction
PostPosted: Sun Dec 14, 2014 10:21 pm 
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Perhaps :| ......but I can frankly say in my decades of selling fine jewelry, no one has ever requested a LIBS report with an item.
But scarodactyl, you are right, there are collectors who are specifically looking for Type IIa Diamonds, enamored with the Golcanda Mystique, or Type IIB because of rarity. I've never seen an ugly Type II Diamond, personally.

And there are so many others who simply fall victim of the descriptive misuse of terms like Paraiba, Chrome Bearing, Kashmir, Copper Bearing and Burma used as quality reinforcement for pedestrian gemstones. A sophisticated buyer relies less on the terms and more on the quality.

My 2¢


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 Post subject: Re: chelsea filter reaction
PostPosted: Tue Dec 16, 2014 12:38 am 
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Barbra Voltaire wrote:
decades of selling fine jewelry

There's the thing. Collectors of odd chemistry for odd chemistry's sake usually aren't looking for it in fine jewelry. But they're certainly a much, much smaller (and odder) group than customers of fine jewelry.

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