Fixer bottle - silver deposit oddity

<p>I store my film processing chemicals in old 2-litre bleach bottles and have done for years. The bottles are well washed out before being used to store working solutions of the chemicals. The bottles are different colours according to the type of bleach they contained. I use that to colour-code for the chemicals. Just recently I started using the white (plain bleach) bottles to store fixer in (the plain bleach is cheaper!) and have noticed that very quickly a dense, black deposit forms on the inside of the bottle even with fixer that has only fixed , say, 12 films. It has never happened before when I used the blue, yellow or green bottles.<br>

Now, do we have any polymer chemists out there? Is there anything in white high-density polyethylene which would cause silver to settle out of the fixer? I wondered perhaps if titanium dioxide was use to colour the HDPE and this might cause the problem, but I'm just clutching at straws here.<br>

TIA.</p>

 

<p>The fixing agents in use today are sodium thiosulfate or more likely a rapid fix formula ammonium thiosulfate. Both, as they age breakdown by oxidation releasing sulfide. This process is known as sulfurization. If this process occurs in a bottled, used fixer solution, the sulfide will bond with silver dissolved in the solution. The result is a silver sulfide buildup on the bottom and walls of the vessel. This material first forms in nooks and crannies and pits naturally present. This buildup occurs regardless of the construction material of the vessel. </p>

<p>I keep my working fix in clear glass coffee jars and I get exactly the same problem.</p>

<p>I believe it is from ammonium thiosulfate fixer losing the ammonia. I never had sodium thiosulfate fixers do it.<br>

<br />I haven't tried it yet, but you should be able to add ammonia to make up for it. Best would be to measure the pH and keep it constants.<br>

Also, be sure that the bottle seals well, and is pretty full. </p>

<p>Thanks for your replies. I have checked the pH and activity of the fixer and it is fine, but I am going forthwith to put the fixer in a different coloured bottle since historically that seems to cause no problems.</p>