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UV MineralsIs it possible to lose fluorescence?

1st Nov 2016 20:43 UTCPavle Jovicic

Few months ago,I received a gift from a friend,one scheelite specimen and he showed me it glows under UV light.Today I bought a lamp but now it doensn't glows at all.Any ideas what is going on ?

1st Nov 2016 20:52 UTCAlfredo Petrov Manager

Probably your friend showed it to you under a shortwave UV lamp, and you bought a longwave UV lamp. Scheelite doesn't fluoresce under longwave UV light.

1st Nov 2016 21:41 UTCPavle Jovicic

Thank you alfredo,that could be it.He used an UV lamp for money,very similar to my.Is it possible to change the ,,bulb'' so i can get shortwave lamp?

2nd Nov 2016 00:40 UTCSteve Hardinger 🌟 Expert

While i have heard of specimens losing their ability to fluoresce (most notably leaving Rogerley Mine fluorite in the sun for too many days)< I've never heard of this happening with scheelite. I believe this is because in the fluorite case fluorescence is due to a changeable impurity (something other than CaF2) whereas in scheelite the fluorescence is an inherent part of CaWO4 molecular structure.

2nd Nov 2016 02:36 UTCRolf Luetcke Expert

Pavle,

There are three main wavelengths used to view fluoresents and the short wave is the one that lights up most fluorescing minerals. It is also a wavelength one can't look into because it will destroy your eyes. They use the same wavelength for disinfecting things in hospitals.

That is why it is so easy to buy long wave lights and soooooo much cheaper, they are not dangerous to look into but only light up around 10 percent of the minerlas, or maybe even fewer.

The good short wave lights are quite expensive and make a huge difference. It is important to look fpr someone who has a good UV lamp to show you the difference.

I think Alfredo was right, you saw the specimen only under long wave again.

Lots to learn but great fun.

Rolf

2nd Nov 2016 03:47 UTCMichael Sommers

Pavle,

You can possibly change the bulb to get a UVC (=shortwave) emitter depending on the type of light fixture you have, but more importantly you would also need to change the filter that blocks the visible light the bulb generates. Those are a bit harder to find and are also fairly expensive. So the effort might be not worth it considering the ease of buying a complete light.

Cheers,

Mike

2nd Nov 2016 08:46 UTCPavle Jovicic

Thank you very much,you helped me alot ! I'm gonna find some shortwave lamp on sale.

2nd Nov 2016 11:43 UTCDavid Von Bargen Manager

If you go for a used light, be aware of the problem of solarization of the filters. The amount of UV light passed through the filter will decrease with time (after 100 hours of use you get reductions of between 20 and 60 %).

For some tests run in the 1980's.

https://uvsystems.com/wp-content/uploads/SOLAR_8_31_90.pdf

2nd Nov 2016 11:58 UTCHarold Moritz 🌟 Expert

Some minerals that fluoresce due to impurities can lose fluorescence, notably chlorophane variety of fluorite, if left out in the light for extended period. But scheelite is intrinsically and forever fluorescent (under SW only), so must be a lamp issue.

There have been great advances in UV light filters over the decades and I'm not sure that anything from the 1980s is relevant. Seems to me that My Way Too Cool is performing as well as it did when I got it in the late 1990s.

2nd Nov 2016 22:22 UTCRolf Luetcke Expert

Harold,

I have two of the Way Too Cool lights and find the same thing, they don't seem to loose much over time. Have had ours for several years but I have burned out a couple of bulbs over that time.

I have one battery pack one and it is great for field work but the battery is quite heavy, sure is worth it for the better results.

I had an old UV light and it is really poor since it is so old.

So, Pavle, be careful buying a used light, a friend did and it ended up having to get the new filters for it and that boosted the price up quite a bit and it is still not a good light.

It may not be possible to use a light if you buy something used online and that would certainly be useful. If you have any major mineral shows near you at any time, that may be the best way to go. Some of the UV lamp sellers have used models they also sell.

A good like makes a huge difference.

Rolf

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