Ah, wetting agents...
A 'wetting agent' (beside being an ankle-biter in nappies) is essentially just a chemical agent that changes the surface tension of water. Some describe it as making water wetter. Normally, water has a tendency to 'bead up' on any hard surface. Tap water contains impurities, and when the droplet has evaporated, these impurities are left behind in the form of visible spots, which we obviously don't want.
We can reduce droplets by removing water, or by reducing the ability of water to form droplets (bead up). Squeegees and sponges and fingers are typically used to remove water from photographic film during the last stage of processing. These can cause streaking or even scratches, if abrasive particles are present.
We can also reduce spotting by reducing droplets. This is what the wetting agent is supposed to do. You may notice that wetting agents, when mixed with water vigorously, tends to foam up. It feels slippery, like soap, on the fingers. It washes off with more water, also like soap. In fact, soap (or detergent or washing-up powder or whatever you call it) is a wetting agent. Is Kodak Photo-Flo 2000 actually soap? Some have said so. I make no such claim, but I believe they have similarities.
We can also reduce spotting by reducing the particulate matter suspended in the water used to rinse the film. Some use distilled water for this purpose, but it should not be necessary. Filtered water has most particulate matter removed that we care about, as well as most of the chemicals that might cause problems (to us or our film), so it should be as useful as distilled water - perhaps more so - not all distilled water is filtered as well. Distilled means it has been boiled and the evaporate condensed and collected, not that it has been filtered as well.
None of these processes will remove the water that is absorbed into the emulsion of the film - that will evaporate in time, and that is why film is not 'dry' just because the shiny side seems dry (also why heated drying is a bad thing). But the spots show up on the shiny side, not the emulsion side, so in practical terms we do not need to be concerned with removing all the water from the emulsion side - time will do that for us.
Mistakes people make with wetting agents:
* Soak the film in it. This allows wetting agent to soak into the emulsion, which serves no purpose. 30 seconds is all that is required.
* Rinsing the film AGAIN with tap water after using wetting agents. This simply washes away the wetting agent - you might as well not have used it to begin with.
* Used in a very strong solution. Typically, the correct ratio is 1:200 as I recall. This is VERY LITTLE wetting agent to a great horking bunch of water. Too much makes the wetting agent itself leave visible residue behind.
For best results:
1) Correct dilution of wetting agent to water.
2) Use filtered water.
3) Short dip in diluted wetting agent, not a long soak.
4) Use some mechanical means to remove the majority of the standing water (fingers, squeegee, sponge, etc) so long as it does not leave scratches. A light touch is best.
Then hang the film in a dry and dustless environment, at room temperature, for at least two hours. One thing to remember now that the Northern Hemisphere is in winter - heat differentials can cause condensation. Film does not retain heat like say a drinking glass, but under the right conditions, it can condense water out of the air like any other object.
Last but not least - stop looking at it! Leave it be, especially if you're an obsessive-compulsive berk! Get a beer and chill or go online for a couple hours.
Best Regards,
Bill Mattocks
PS - In answer to the original question, "Can a wetting agent go bad?" Ask any parent of teenagers.
