View Full Version : Fluorescence in acid stop bath?

Doremus Scudder
3-Nov-2007, 07:14
Running some tests today with ascorbic acid added to double-strength PMK (to see if I can increase developer activity somewhat for expansions). I was using PMK 10ml A, 20ml B to 500ml water with an added 10ml of 5% ascorbic acid (2:4:100 + ascorbic acid to 0.1g/liter).

When transferring the sheets of film from the developer to the weak acid stop (half-strength or less Kodak Indicator Stop), I noticed a faint, but definite, fluorescent-type glow. the glow spread through the entire tray and illuminated the film sheets from behind. It lasted 4-5 seconds or so. The film seems unaffected.

Has anyone heard of this phenomenon? I'd love an explanation. It has never happened to me before using other developers (HC-110 and regular PMK mostly).

Thanks in advance.

Doremus Scudder

Arne Croell
4-Nov-2007, 00:31
It is probably Chemoluminescence - apparently Pyrogallol is capable of it:


Doremus Scudder
4-Nov-2007, 03:56

Thanks for the answer and the link. I suspected that I was using the wrong term, chemiluminescence it is indeed, and pyro reacting with the acid stop seems to be the cause. Fluorescence is light (visible) emitted due to absorption of energy (photons) of another, shorter wavelength (usually invisible, e.b. ultra-violet). Chemiluminescence is light emitted due to a purely chemical reaction (bioluminescence when found in living things, e.g. fireflies).

Some further research on APUG and the AZO Forum turned up a bit more about this phenomenon. It seems that users of ABC Pyro experience this "pyro glow" regularly. Other pyro formulations also luminesce when film developed in it are transferred to the stop bath, but PMK is not among them.

Any more info (just out of curiosity) about why pyro does this would be appreciated.


Doremus Scudder

James Morris
21-Aug-2011, 06:48
I noticed this tonight with wd2d+ and kodak indicator stop bath. Wow!

Does anyone know if it fogs the film?

22-Aug-2011, 10:15
I once noticed that jugs of distilled water I had placed on the floor in my darkroom were glowing faintly. I started getting quite worried since I had also used another jug as drinking water. Turned out there was a slight bit of light leakage from a crack right behind the jugs, which caused them to appear as though they were glowing in the dark.