As it turns out with my experiment to use this big jug of stock solution in post #1, I mixed up some at 1:5 last night, and used it to make some contact proofs. The working solution turned out cloudy and fairly stinky. But it DID seem to fix OK, although I have no idea if it's leaving residual silver. It would be a shame to just get rid of it, as I sure do have a lot of it.