PMK Pyro working solution color change

[Mei Leng]

Have used PMK pyro for several years. When A & B is mixed together the solution changes color from gray green to pale amber. No problem even with solution stored for 3-4 years. Made up 2 liters of solution A March 2012 and divided it into 4 brown glass bottles. Used up first bottle with no problem with color change when mixing solution A & B. Just started using second bottle of solution A. There is color change from gray green to place amber but the color change is much weaker, gray green much lighter. Mixed up fresh solution B, color change still the same, much lighter. Not much staining with HP5 plus and FP4. I only use distilled water. Any reason why color change is weaker?

 

[Doremus Scudder]

PMK stock solution A should be a light yellow/straw color, not "grey green." When the working solution is mixed, it turns amber. I have had different batches of PMK turn a lighter or darker "amber" and still work well. When solution A goes bad, it turns a very dark brown from oxidation. If your stock solution is still light colored, this is likely not the problem. What you seem to be describing points to a weak solution A, i.e., a too-high dilution, not enough chemical (pyro) in solution, or contamination. Since you mixed this all at one time and divided it into bottles, try some solution A from one or both of the other bottles. If they work better, you can assume that bottle 2 was somehow contaminated. If they are all the same, and deliver poor results, maybe all of them are suspect. This you could only verify by mixing up a fresh batch.

Hope this helps,

Doremus


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