Photographic Lab Handbook

Apr 6 00:57 UTC 1995

This subject is to offer data from "the photographic Lab Handbook"[D[D[D 
by John S. Carroll.  If anyone is a B&W home processor and wants film data
or chemistry, let me know & I will try to look it up for you.
This is good for times/temperatures for various developers on B&W films.
My handbook copy is old, so I do not think it covers T-max.

response 2 of 9:

Jul 29 21:22 UTC 1996

re#1:  how much do you need?  i might be able to give you some out of my
        x-ray darkroom.

response 4 of 9:

Jul 30 16:07 UTC 1996

Well, I use it at about a gallon at a time...and I usually try to squeeze out
as much use of the fixer as I can.  Sometimes, I go through 3 changes of
developer for one change of fixer.  I can hold you a quart, or gallon, next
time it's changed if you have a bottle for me to put it in.  I'll have to
check with my office manager to see when it is due for changing.

response 6 of 9:

May 15 05:06 UTC 1998

Rick did provide me with spent 'hypo' (thanks!) and it did sit around for
a while, but this week I finally tried to plate silver on copper with it. 
I set up my copper disk as the cathode and used carbon rods for the anode,
and somewhat arbitrarily chose a current of 2 ma/cm^2. I added the 'hypo'
and turned on the current - and copious flakes of silver swirled off the
copper disk. I also tried it without current, and only a very loose plate,
easily rubbed or even washed off was formed. The problem is that the
thiosulfate complex of silver is not 'strong' enough to reduce the free
silver ion concentration to a point where it does not spontaneously react
with copper (copper being more electropositive than silver). 

I am now considering adding cyanide to the used hypo, to complex the
silver as the cyanide, which is what is usually used for silver plating. A
problem is to know the concentration of silver (and unused 'hypo') in the
used hypo, for estimating the amount of cyanide required (and dilutions
necessary to attain the silver cyanide complex concentration recommended
for plating).  Therefore this is the right item - what does the handbook
say in answer to: 

1. What is the usual concentration of sodium thiosulfate in 'hypo',

2. What fraction of this is likely to have been consumed in the used
   'hypo', conventionally?

3. About how much rinse is likely to have been carried over into the
   'hypo' during film processing, until the 'hypo' is exhausted?

I would be glad for information or speculation on any of these matters,
although I would only need rough estimates, as I think the silver will be
titratable with cyanide - that is, solid silver cyanide will first
precipitate as cyanide is added, and then redissolve as the complex with
further addition of cyanide. However I don't work with cyanide unless I
have planned ahead to the extent possible.

response 8 of 9:

Jun 2 19:31 UTC 1998

I intend to get a stainless plate (for the cathode) and try just plating
out the silver. (If that works OK, I may be looking for more used hypo. 
From silver I can make silver nitrate, and prepare a proper silver plating
bath from that.) 

After looking further into plating directly from hypo, it appears I would
have to complex all the silver anyway with cyanide after neturalizing the
used hypo's acidity. Another problem is that ammonium thiosulfate was used
in the hypo, so it will form free ammonia when made alkaline, and free
ammonia attacks copper. It looks like it would take a lot more
experimentation to get a coherent silver plate directly from used hypo. My
inquires on usenet if anyone had done it also met with no success.