Quote Originally Posted by Doremus Scudder View Post
I would love a quick, easy and accurate test to determine the dissolved silver content of my second fix. I don't think one exists that is practical, so ST-1 it is!
Hi, my best answer to this is with the silver estimating papers. If someone has a copy of the old Kodak procedure, the method is well described. And ideally, you have a color reflection densitometer. The downside is that you need to pay a testing lab the fee to run silver analysis on a half-dozen samples, or so, so I'd guess a charge of a $100 or $150 (this is a wild guess). In the old days, these would have been run on an AA unit, but in more recent times, one of the chemists here (Kirk) says more likely on an ICP machine.

Basically, you assemble a set of your own fixer samples, covering a range from, say, 1/4 gram per liter up to 2 or 3 grams per liter. Pick a certain size sample container - we used those little disposable Solo cups (maybe 3 oz?). Suspend the test paper, motionless, for 30 seconds. Remove and quickly rinse with fresh water, then dry under warm air. Read the density (I think a blue-filter reading was recommended, but visual would probably work.) At the same time, a duplicate set of samples goes off to the analytical lab. (Make sure they know what they're reading, and give them a general idea of the range.)

As I recall, plotting the density vs silver content has a gentle curve, slumping off near the top; I don't remember exactly. It's probably accurate within about 10%, in the general range of 0.3 up to about 1.5 g/l, as I recall (fuzzy memory). To check unknown sample, do the dip test, dry it, read the density, then look it up on the graph. We used this method in a large photo lab for quite a few years, until we eventually got an AA unit in our chem lab.