Regarding your comments on black lacquer fluorescing, you might be interested in the article
“A Summary of Ultra-Violet Fluorescent Materials Relevant to Conservation” at
https://aiccm.org.au/national-news/summary-ultra-violet-fluorescent-materials-relevant-conservation.
There it is!
I noted his query myself and did a short search but didn't find anything as definitive as that.
For GAD's "scientific" explanation let's start by defining fluorescence, from the
usual source :
"Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence."
So it's an accepted "given" that NCL lacquer is stimulated to emit a greenish light when stimulated by UV radiation, but
why?
I wondered if it was the cellulose or the solvents, or both.
Saw a comment in one blog that
cotton t-shirts fluoresce and thought "
There's an indicator!", but one commentor mentioned the use of optical brighteners in laundry detergent being the cause.
I wasn't satisfied that was completely correct but dropped it at that point.
Now your source indicates cellulose itself, the primary constituent of cotton fiber and indeed a primary source of NC itself, going all he way back to "gun
cotton"
does fluoresce.
Bingo.
Followed immediately by 2 more derivatives of cellulose (cellulose acetate and the primary form in question here, cellulose
nitrate) which fluouresce at a different wavelength (color) than "plain" cellulose.
GAD also mentioned seeing this as confirmation that these late Westerly Starfires were NCL finished which kind of suprised me because I never had any question about it, but going back and reading the '96 catalog and
Guild Gallery #1, I can only find specific confirmation that
all the
gloss finished
acoustic guitars were indeed NCL.
I do know that Hans has said in past that they did "experiment" with poly in Westerly but only recall ever seeing one specific model ID'd (not a Starfire).
So GAD's uncertainty about the true nature of the finish is understandable.
I didn't think they used poly on hollow/semi-hollow electrics until Corona (X-150's, IIRC), but am now no longer as sure as I was 10 years ago.
Have even seen some compelling evidence to suggest that at least some late (post '94)
satin finishes on
acoustics are in fact poly, but still only demonstrative evidence and owner claim, not yet corroborated by somebody like Hans or Jay Pilzer, that I know of.
After all that, what still "gets" me, is if NCL generically fluouresces, why is a blacklight test supposed to detect repairs?
Possibly the difference in age of the finishes, ie, the fluorescence increases with age?
Something to do with the yellowing of the lacquer, perhaps?
Or maybe because the NC content itself is increasing since NCL continuously outgasses its solvents as it ages, and becomes increasingly crystalline in structure?