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why does a blacklighted guitar glow?

LowE

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I know some of the answer, but not all. First you have to know that a blacklight tube is a type of flourescent lamp (FL) as opposed to the regular domestic light bulb which is incandescent light (IL). An old fashioned IL works by basic heating up of a coiled metal filament (usually tungsten) via electricity, and the metal glows hot and gives off visible light which you can see.

With a flourescent tube its not the heat, but a mercury gas inside the tube which when excited by the electricity causes ultraviolet light to be emitted (from the mercury). A FL only sheds visible light if you coat the tube with a material that glows when exposed to ultraviolet light, otherwise, if it were just plain glass you wouldn't see anything at all, there'd be plenty of UV light emitted but it'd be pitch black in your room. The material that you coat a FL with is called a phosphor, and can be any of a range of materials that emit visible light (different colors depending on the material) when you shine UV light on it. Black lights are just like regular flourescent lamps, but instead are made of a glass tube that is black instead of clear (to absorb bad UV I believe), and it is coated with a phosphor that glows faint purple when exposed to the UV light. With a blacklight, there is both visible light being emitted in the purple frequency (the lowest freq), and there is also a lot of UV light emitted you can not see.

When you shine your black light on a guitar, you are seeing two effects. One is the simple reflection of the visible purple light that is coming off the tube and lighting up the room - and the other is the reflection of the UV light off the guitar, which can ONLY be seen by your eyes if there is some phosphor on the guitar. If there's no phophor on the guitar, you'll only see it normally in the room like everything else that is reflecting the visible purple light. But if there is phosphor, which I assume is in the yellow pigment of the nitro, and possibly in some poly too if it's yellow or otherwise tinted, then you will see glowing visible light due to exposre to the UV.

What I still don't understand is what kind of phosphor is in the nitro lacquer, and how does it react to exposure to sunlight?

When you look at a typical old Fender, the decal is over the finish and somehow protects the phoshor below it. It glows bright compared to the headstock. Protects it from what? From oxidation, from sunlight, something else?
 

Rev.WillieVK

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From Wiki:

"Fluorescent black lights are typically made in the same fashion as normal fluorescent lights except that only one phosphor is used and the normally clear glass envelope of the bulb may be replaced by a deep-bluish-purple glass called Wood's glass, a nickel-oxide–doped glass, which blocks almost all visible light above 400 nanometers. In practice, partly due to cost but mainly because Wood's glass does not make a satisfactory material for lamp manufacture, the lamp will be made from normal glass and a relatively thin coating of a UV filtering material is applied to the exterior. The color of such lamps is often referred to in the trade as "blacklight blue" or "BLB." This is to distinguish these lamps from "bug zapper" blacklight ("BL") lamps that don't have the filter material

The phosphor typically used for a near 368 to 371 nanometer emission peak is either europium-doped strontium fluoroborate (SrB4O7F:Eu2+) or europium-doped strontium borate (SrB4O7:Eu2+) while the phosphor used to produce a peak around 350 to 353 nanometers is lead-doped barium silicate (BaSi2O5:pb+). "Blacklight Blue" lamps peak at 365 nm."
 

LowE

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I think the reason we see snot green under black light is that there's a mix of the yellow pigment in the nitro glowing from the UV exposure, together with the blue color of the visible light - which combines to make green. I'd really like to see a guitar in a dark room exposed to UV light only, with no visible light component. That would give a truer indication of what color the phosphors in the nitro really are.
 

Rev.WillieVK

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I once saw a '50s LP in a totally blacked out room lit only by a 4' black light setup. The greenish-yellow glow was almost blinding!

Assuming for a moment that it is the phosphorus that glows, where is the phosphorus coming from? There is no phosphorus in nitrocellulose. Nor is there any in regular nitrocellulose lacquer.

Could it be nitrates that are lighting up?
 

LiveOak

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In the early '70's, I used Murine eye drops right before a gig to get rid of my red eyes from obvious chemical exposure (self induced) and everybody started to freak out when I got up and started to play under the black lights because the murine drops that ran down my face after I applied same to my eyes glowed! Early KISS! LOL!

I think the Fender Jaguar I was using at the time glowed as well, but not sure.
 

LowE

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I once saw a '50s LP in a totally blacked out room lit only by a 4' black light setup. The greenish-yellow glow was almost blinding!

Assuming for a moment that it is the phosphorus that glows, where is the phosphorus coming from? There is no phosphorus in nitrocellulose. Nor is there any in regular nitrocellulose lacquer.

Could it be nitrates that are lighting up?

I don't think it needs to be phosphorous, but any material that glows under UV. What is it in nitrocellulose or other lacquers that makes it yellow, or makes it yellow with age? I think that's the stuff that's glowing under UV.
 

AtomEve

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Aug 5, 2002
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I've had many guitars from the 90's that glow much brighter than guitars from the 50's. it's no help in determining age, only helps to see inconsistencies in the finish.

Exactly! :salude :applaude
 

guitarvoodoo

Formerly fishnose, Les Paul Forum Member
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Hmm.... :hmm
PAF tape and PAF stickers often light up snot green too, and there sure ain't no nitro finish involved there...

/GV
 

LowE

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Hmm.... :hmm
PAF tape and PAF stickers often light up snot green too, and there sure ain't no nitro finish involved there...

/GV

Yep, so do your teeth and lots of other things that don't have nitro finish.
 

AtomEve

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Yep, so do your teeth and lots of other things that don't have nitro finish.

Like human fluids for instance.... just sayin......

Never bring a blacklight to a hotel room....... :wah
 

Litcrit

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When you blacklight an old 335 (maple body/mahogany neck) I notice a different glow from the different woods. How can you tell if there's been a partial refin in that case?
 

Tom Wittrock

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When you blacklight an old 335 (maple body/mahogany neck) I notice a different glow from the different woods. How can you tell if there's been a partial refin in that case?

Strip the finish and blacklight only the finish? :ganz





Or not. :spabout
 

alainguitars

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May 21, 2003
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When I was selling my 57 LP Custom a well known dealer blacklit the paf's in the guitar. He told me one sticker didn't glow as much as the other one. Left a bad taste in my mouth, Seemed like the predictable talk the price down bullshit. Anyone else blacklight paf stickers for authenticity?
 

Joe Desperado

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Litcrit, the 335 should basically blacklight the same all over. You may see differences in the overall color/shade or density of the yellow/creamy blacklit color, but it should be consistant. When an area has been resprayed or touched up, the newer area will be quite obvious. Usually you will see a cloudy area under the blacklight that looks much more dense or even a color change at the work area. The only times I have seen something simular to what you were stating is when I did a total neck refin. I taped off the neck right at the mahogany/maple joint. The neck was a total refin and looked consistant under the black light and body was original and looked consistant under the black light. The only part that show any signs of the change was right at the joint itself. This is where the new finish and the old finish melted together. It was about a 1/16" line that looked slightly different.

Also what I am now seeing with my own repairs is that if I spray my clear with amber dye in it, it will black light a lot more like an old guitar. So my latest trick has been to restore the guitar and then shoot a clear coat that has amber in it. I can get it to glow an awefull lot like the older finish.

In the end, there seems to always be some tell-tale sign that work was done. The better you are at repairs, the hard it is to find the signs. I am still getting there. At times I feel I nail the repair and its almost undectable, and other times, no matter what I do, I can't seem to make it disapear.
 

Joe Desperado

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Here is a 57 Gretsch with work at the heel. (I DID NOT DO THIS REPAIR). The original finish is rough and this green is hard to match. In person, it looks pretty good, but here is what it looked like under the blacklight.


0142_12.jpg


055e_12.jpg
 
L

LPDEN

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I was always amazed at how the black light reveals so much more that is not there in normal lighting.
 
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