I started out using Kodak's published 1:200 recommendation, but constantly had problems with spots on the film. I use tap water (probably average hardness?).
After reading somewhere on APUG that Photo Flo sometimes works better at half the concentration, I switched to 1:400. It's worked great ever since then. No spots on the film at all anymore.
I add about 20 drops to 1.25 liters of distilled water, and use this for many rolls, until I notice a hint of a problem. Then I add about 10 more drops. At this point, weeks have passed and I mix up a new batch.
I don't like to use much Photo-Flo, as this way I find it easier to rinse from my equipment The tank I use for soaking in this solution is dedicated to the task, and rinsed after use. I started this after I noticed some build-up in one of my developing tanks.
I use a small drop dispenser, that gives little drops.
Some time ago I counted out how many drops there were in 10 ml of photo-flo concentrate (120). For 1:200, that would be enough to make 2 litres of working solution. I then divided that number by 10, to get the number of drops for 200 ml of working solution (12).
I mix up a batch of photo-flo working solution (usually 300 - 500 ml) and then use that same batch with every roll I develop that day. At the end of the day, I discard it.
I use tap water, and generally have no problems.
“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
I've been using Photo-Flo 200 at about half strength or a little less with great success for years now.
That said, I also use some other products successfully. I have European Kodak Photo-Flo (not 200) that is principally ethylene glycol that works well (a different ingredient than Photo-Flo 200). I've also used the Zone VI product (not sure of the ingredients, but I've still got half a liter sitting around somewhere in the States) with success. Both of these I use at half-strength or less as well.
However, I always use distilled water for the final rinse after washing.
Theoretically, if the emulsion is well-saturated with distilled water, and drops are removed from the film surface, a wetting agent shouldn't be needed at all, since there are no minerals, etc. in the water to leave deposits; and the distilled water should all evaporate away leaving nothing behind.
The danger when there is nothing to deposit on the film seems to be marks left when the emulsion dries at different rates, with lines at the interfaces around drops, etc. The wetting agent serves to prevent drops remaining on the surface of the film so it dries evenly. Therefore, it would seem to make sense that, when one is using distilled water as a final rinse and there is little or nothing in the water to cause marks by deposit, the minimum amount of wetting agent necessary to prevent drops forming would do the job just fine.
I'm not sure how the wetting agent prevents mineral deposits from forming when hard water is used for the final rinse. Perhaps it simply distributes it evenly over the film surface. With harder or more mineral-laden water, more wetting agent may be required to prevent visible deposits... It is likely that Kodak's recommendations are for a worst-case scenario, and that one can use significantly less when one uses distilled or demineralized water.
The fact that greasy anti-foaming agents, etc. are often a part of wetting agents would prompt me to use the minimum possible. Perhaps some tests are in order to see just how little will do the job now...
At any rate, it might be interesting to expand your informal poll to include water quality. How much Photo-Flo does it take to do the job with fairly hard water as opposed to demin or distilled? There is likely a significant difference.
I used to use 1/2 capful of photo-flo per liter of distilled water. Then the packaging changed, and the caps became enormous. I now use a few drops per liter of distilled water, just enough to make the rinse flow without foaming.
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You are right when you say that a wetting agent helps water to sheet off the film when it is hung up. Other than that it cannot directly help with hard water as these solutions do not contain any sequesting agents.
Originally Posted by Doremus Scudder
You can buy a liter of Triton X-100 from www.thechemistrystore.com for a few dollars. This is more than a lifetime supply for most photographers. Adding 75 ml of the X-100 to a liter of isopropyl rubbing alcohol will make a very useful wetting agent. The X-110 must be diluted as it dissolves only with difficulty in water.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.
~Antoine de Saint-Exupery
We use Photoflo 2100 -- that's one part to 2100 parts water. The gallon we have is lasting a long time!
I actually make a stock solution, adding 7 or so oz (don't have the number in front of me) of the 2100 concentrate to make one gallon of stock solution. One oz of the stock solution is used to make a gallon of working solution. And I advise our lab assistants to be generous with the water -- that making it even at half-strength it will still work...but by all means never make it any stronger.
At least with LF landscape, a bad day of photography can still be a good day of exercise.
Originally Posted by Gerald C Koch
You are right, one uses propylene glycol and the other is using ethylene glycol as it's main ingredient. Edwal LFN is using ethoxylated alcohols. This is getting confusing.
Originally Posted by Doremus Scudder
Glycol is just the solvent for the actual wetting agent (Triton X-100 in this case?). It probably doesn't make any significant difference whether it's propylene or ethylene glycol. It's just "stored" in glycol.