Tuesday, December 11, 2012

Developing Film And Water Spots

Following on from my blog posting titled Odds and Ends In B&W Film Development I  thought I would continue with the topic of the final rinse.

Final Rinse Update - In the past I had spots now none:

The final rinse is 3 minutes in distilled water; After the 3 minutes I  then add 1 drop of Edwards LFN wetting agent.; Shake really well for 5   seconds, wait  until any foam dies down; Then remove film from liquid. Shake off excess water and hang to dry.

Absolutely no spots!

Notes:
The distilled water adds  about $0.15 per roll but it seems to be worth it, The trick seems to be prior to adding the wetting agent leave the film in the distilled water for long enough to dilute (replace) any of the tap water in the emulsion.
Over washing and washing the film like a raccoon can do irreparable damage to the emulsion.


Obviously if you get white spots with tap water you need distilled for the final rinse if you don't get them then you don't.. And of course negatives without white spots and drying marks are better than those that have them.

I did an experiment watching under a microscope one drop of distilled water and one drop of my tap water dry on a microscope slide. Absolutely no observable difference! So why use distilled water? Distilled water removes most minerals from the film gelatin layer so it doesn't come to the surface later and cause water marks when it drys. The final rinse must be long enough for the gelatin to become in equilibrium with the rinse water. The reason I reuse the same "distilled" water from the final rinse for the photo flow or wetting agent stage is that I want the water within the gelatin to be in equilibrium with the water that has the wetting agent. This and a short cycle time with good agitation keeps the wetting agent surfactant mostly on the surface where it belongs. It's all about chemistry, surface chemistry, diffusion and equilibrium.

Why not dishwashing soap instead of a wetting agent? Because it's a false economy and they contains impurities, contaminants that could cause problems. Wetting agents designed for film do not have the extra impurities that are added to dish water soaps and are only a couple of pennies per film.

Tip: 

Sometimes I find stuff floating in my developer or fixer, to remove pore the liquid through a small fine stainless sieve used for cooking. Don't forget to rinse the sieve after using to prevent corrosion.


Drying

 I recently I brought an old Kindermann Rapid dryer. I then taped a dust and pollen filter over the fan air inlet so for a total cost of $20 I can now have dry, dust and spot free film ready to scan within 45 minutes of development.

There are many DIY dryers out there on the web including those made with garment bags. This MacGyver like method although I haven't tried it yet, it looks brilliant!


Warning

Depending on your water the use of distilled water may be dangerous overkill. A friend of mine after many years of no problem started to have problems with spots this went on with the spots getting worse over the year, Finally he gave me a spotted frame which under a microscope showed fine surface crazing all over with the spots caused by more severe surface damage rather than by left over chemical residue. With the proof he finally followed my advice and used the Ilford method of rinsing. Suddenly no problems! His problems started when in his own words "Someone told me I should rinse more so I started to rinse more and the more I rinsed the bigger the problem so I added more rinsing aid and more distilled water. Ended up rinsing  like a Raccoon." 


References

Why Is Water The Universal Solvent
Diffusion
Surfactant
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