Quote Originally Posted by Photo Engineer View Post
You see why this method is not just for anyone? Also, there are standards, as I have stated before, for retained HQ and Metol, but there is no good test for them either.
I used to perform the Methylene Blue test for residual thiosulfate in microfilm (the microfilms were of records from a nuclear power plant).

I remember the test being harder to set up than it was to actually perform it.

The NND reagent is a bit hard to make - you have to get the oxalate salt of the NND and then it's dissolved into concentrated sulfuric acid and it takes a bit of time to get the NND into solution.

The borohydride solution is pretty hazardous, and it doesn't last long in solution.

I've got the bottle of sodium borohydride in my basement as the lab I worked at tossed a bunch of old reagents, and I saved the borohydride from the waste stream. I'm sure I rescued the NND reagent, but I have no idea where I put it... :^(

Other than needing to have a spectrophotometer, it's really not a difficult test to do. It would take a few hours for one strip of film from start to finish.