Using conductivity to determine emulsion wash

John Sager · Feb 23, 2015

Hello everyone,

I am looking to improve my noodle washing. I have seen reference here and elseware of using conductivity to determine when a wash is complete. PE's book discusses using a silver nitrate solution added to a sample of wash water. Other techiniques just go by a standard routine that has worked for them in the past. That is what I am doing now but it does not appeal to the German side of me. I have a conductivity meter but i am not sure what conductivity value to use as an indicator of a complete wash or if using conductivity as an indicator is even appropriate. I use chlorene free reverse osmosis filtered water for washing. I have not measured the conductivity of my prewash water yet but expect it to be in the very low 100s uS/cm.

Also I see differing views on using distilled water for washing. I thought in lue of using distilled water and adding salts (it appears people are doing this but please correct me if i am wrong) the filtered water might be a good (cheaper) option?

Any ideas are very much appreciated.

Thanks.

dwross · Feb 23, 2015

John,

Distilled water is definitely not recommended. The noodles absorb way too much water. Tap water would generally be OK (unless you have iron in your water) except that it seems municipalities everywhere recently have begun to really pour on the chlorination --> fog alert! I have access to good spring water at my grocery store. I use that for noodle washing. Nick at GEH has been experimenting with a Brita filter. That seems to be going well for him.

re conductivity testing: A simple pH meter will do. I used one when I was first getting started, but quickly decided that was OCD overkill. For many years now, my process has been to wash thoroughly and then add back in some KBr (as a 10% solution.) It takes very little trial and error to decide the best least amount necessary for any particular recipe.

my 2 cents,
d

John Sager · Feb 23, 2015

Thank you Denise,

I am actually trying to reduce the fog a bit. I started by replacing a safelight that was not ummm... safe and repairing a darkroom that was not dark. Now trying to work on my washing technique. I have a stockpile of beautifully coated plates that I am finding are probably only good for a sun shade in a greenhouse! Maybe not quite that bad. With each change my emulsions are getting a little better so maybe there is hope.

dwross · Feb 23, 2015

Hope indeed!
Silver gelatin is perhaps the ultimate dive into deep craftsmanship. That whole mindset/challenge/goal, whatever the subject, is kinda getting lost today. There are a lot of really easy ways to do most things. I totally get that. You can't do everything. I haven't canned tomatoes in a long, long time! But, I think most people need (perhaps even on a spiritual level) to master at least one deeply satisfying craft. I think it's hardwired into us.

I just got done with a marathon of new recipe development that took five tries, one after another to nail down. Three days ago, I was tearing my hair out, and this morning I'm shamelessly happy and proud. You can't beat that for squeezing all the juicy goodness out of our limited time under the sun.

Best of luck with your next plates! I hope you post pics here.
d

bernard_L · Feb 23, 2015

the German side of me

You might read these; the author, coincidentally, is also German.
http://www.suessbrich.info/foto/duka/ilfw/photogra.html
http://www.suessbrich.info/foto/duka/ilfw/ilfwash.pdf
As an aside, this article convinced me to use the "Ilford method" for washing films; I should someday check with HT-2.

Photo Engineer · Feb 23, 2015

John, I use distilled water. I overwash and then either use the emulsion right away or I add some bromide in. It would be useful to use about 0.03 g/l, which would bring the emulsion to about 100 mv. Nick and I both have had trouble with city water lately and filtration does not seem to work well.

Don't worry about the DW, but if you do worry about the swell, try using some Magnesium Sulfate or Calcium Sulfate in your DW. Just a little will reduce swelling. Nick measures the volume of his emulsion before and after wash and finds an insignificant difference between city water and DW volume after wash.

I'm expecting a call from him this PM, and if I do, I'll check up on this. It is pretty snowy here today, so this might not take place.

PE

John Sager · Feb 23, 2015

Thank you PE. I appreciate all your help.

kb3lms · Feb 23, 2015

Time for a quick work break.

John, I will vouch for the use of Magnesium Sulfate in distilled water. My method is to add 1 tsp of MgSO4 per US gallon of DW. There is very little swelling of the noodles. I haven't tried Calcium Sulfate since I don't have any but AFAIK it works just as well. My house has well water, but it is full of iron so I don't use it.

As far as measuring conductivity of the wash water is concerned, I started going down that path and then tried PE's advice of using a silver nitrate solution. OTOMH I forget the concentration. Anyway, after each wash cycle take 100ml or so of the discharge water and add 2 or 3 drops of silver nitrate. A cloud of silver halide should form. Continue washing until when adding the AgNO3 drops there is just the tiniest hint of a cloud left. For me, I find that this is usually about 8 cycles.

If you really want to try the conductivity route, a number I have seen repeated twice is 1800 x 10^-6 mho/cm. I cannot vouch for that specification, I simply have seen it repeated in two different, unrelated formulas.

-- Jason

Photo Engineer · Feb 23, 2015

If you do use conductivity, do NOT use calomel electrodes in the emulsion itself. They contain Mercury and will fog the emulsion. See: http://en.wikipedia.org/wiki/Saturated_calomel_electrode

In place of the standard electrode, you might want to use a Silver/Silver Chloride electrode.

I forgot. Nick just called. I checked. He is using plain DW with no problems. He does not use Brita filters.

PE

John Sager · Feb 23, 2015

Excellent information. Thank you. I think for my next batch I will try the silver nitrate check. Although there is no number associated with it, which pains me, it is simple enough. What concentraion should the silver nitrate test solution be?

dwross · Feb 23, 2015

Nick is such a ideal person to have shepherding silver gelatin at GEH (with a lot of help from his friends, of course!). He used a Brita successfully when he thought Rochester water might be causing problems. It wasn't, so he stopped. He's using distilled now in order to standardize everything to the greatest extent possible for his students when they go home. He says distilled is working fine. That's fascinating. Heck, silver gelatin is fascinating. The lack of problems might be related to modern gelatins (??). I have excellent luck with a local brand of spring water and it's lot cheaper than distilled. I think if you avoid chlorine and iron, it's probably all good.

Using conductivity to determine emulsion wash

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