Photo Flo

The light sensitive goodies that comprise film are held in place using gelatin as the binder (glue). Gelatin is chosen because it is transparent, flexible, and permeable (fluids can enter and exit effortlessly). When film enters the developer, which is mainly water, the now wet gelatin swells. This this promotes the permeability. After all the steps of the process are complete, the film is air dried.

During the drying stage there are perils. Residue in the form of particulate matter can remain and will blemish the film. Since the gelatin is glue-like, these particles can become imbedded.

As the film dries, the gelatin shrinks back to nearly its original thickness. Now water has a surface tension that promotes beading. We are talking about water droplets that are scattered on the film’s surface. These droplets retard drying in the area beneath them. Thus the film’s shrinking rate becomes uneven. After drying is complete, the thickness of the film will be uneven if these beads were present. Worst, the area under the beads show, we call this a drying mark. These can permanently blemish the film.

An ounce of prevention is worth a pound of cure. PhotoFlow is a surfactant that breaks the surface tension. A trace amount of this surfactant in the final rinse will cause residual water to sheet up and thus not bead up. This simple remedy promotes uniform film drying.

It's very very cheap and very effective. Well worth the extra step.

Thank you!

The light sensitive goodies that comprise film are held in place using gelatin as the binder (glue). Gelatin is chosen because it is transparent, flexible, and permeable (fluids can enter and exit effortlessly). When film enters the developer, which is mainly water, the now wet gelatin swells. This this promotes the permeability. After all the steps of the process are complete, the film is air dried.

Thank you so much for all of that information! It really helped!

 

During the drying stage there are perils. Residue in the form of particulate matter can remain and will blemish the film. Since the gelatin is glue-like, these particles can become imbedded.

 

 

As the film dries, the gelatin shrinks back to nearly its original thickness. Now water has a surface tension that promotes beading. We are talking about water droplets that are scattered on the film’s surface. These droplets retard drying in the area beneath them. Thus the film’s shrinking rate becomes uneven. After drying is complete, the thickness of the film will be uneven if these beads were present. Worst, the area under the beads show, we call this a drying mark. These can permanently blemish the film.

 

An ounce of prevention is worth a pound of cure. PhotoFlow is a surfactant that breaks the surface tension. A trace amount of this surfactant in the final rinse will cause residual water to sheet up and thus not bead up. This simple remedy promotes uniform film drying.

Reduces spotting on negatives - reduces surface tension of water so drops "flow" off negatives more readily. Cheap, easy, good idea.

Thank you!

Thank you!

You're certainly welcome, but Alan is the Man! More detail than I ever knew.

T

(snip)

As the film dries, the gelatin shrinks back to nearly its original thickness.

(snip)

I suppose the gelatin does go back to the original thickness, but the whole emulsion shrinks.

White light holograms use a thick emulsion, such that the interference pattern is within the thickness, and silver is deposited in appropriate layers.

But since the emulsion shrinks, the result is that the interference is with green light, instead of the original HeNe red light.

@alan_marcuse

Dear Alan, thank you so much for all these information. I appreciate it! It was very informative.

"What is photo flo?"

- It's washing-up liquid without the scent or colourant added. That's all.

If you use liquid detergent for your dishes then you can use that in place of photo flo.

"I believe a water spot will actually change the grain distribution a bit at the edge of the drop....."

- Where did that piece of misinformation come from?

'Grains' are not mobile within the gelatine matrix. To move them about you'd have to melt the gelatine, and a cold water droplet won't do that.

Photo-flo MSDS here- https://intranet.ssp.ulaval.ca/cgpc/fsss/fichiers/Photo-Flo.pdf

It's mostly water, propylene glycol and a wetting agent. Though the wetting agent is similar or the same as used in various detergents, and people have used such in a pinch, it's not really recommended because the constituents of detergents vary all over the place and you can't be sure of what you're bathing your film in.

As for the grain pattern, look at a dried water spot under a microscope and reach your own conclusion. Maybe it's an optical illusion, but still darn hard to fix by rewashing.

If you use liquid detergent for your dishes then you can use that in place of photo flo.

Really not a good idea.

The disadvantage to using soaps is that they contain dyes and fragrances which can color or leave oily droplets on film and paper. They can also increase tackiness. Then your film or paper can stick together in humid weather.

One bottle of Photo-Flo can last a lifetime.

"As for the grain pattern, look at a dried water spot under a microscope and reach your own conclusion. Maybe it's an optical illusion, but still darn hard to fix by rewashing."

- I suspect what you're seeing is a hard water deposit (limescale) and not 'grain'. Limescale will not redissolve in water alone, but a citric acid solution should dissolve it with no detriment to the gelatine or image. It would be no worse than an acid stop bath after all.

Those lucky enough to live in a soft water area, or having a softened and filtered water supply, won't suffer from visible dried water spots.

"The disadvantage to using soaps is that they contain dyes and fragrances which can color or leave oily droplets on film and paper."

- You'd have to use a ridiculous amount of dishwashing liquid for that to happen.

Compared with the additives and contaminants in many domestic water supplies - lime, phosphates, chlorination and fluorination for example - the non-detergent ingredients in dishwashing liquid are insignificant at the few parts per million caused by adding one or two drops to a gallon of water.

Time was when almost any photographic shop (find one of those these days!) stocked photo flo or some brand of wetting agent. Those days are gone. So if you don't want to buy online, you're left with little choice but to use an easily obtainable and harmless substitute.