Originally Posted by Paul Verizzo
Take some of the same film that you are using. What you want is a sample of exposed leader. Of course, being C-41, it should be any color neg, but the universe is perverse.
Plop it in a bit of the fixer in question, and time the, um, time until clear.
So I tried your suggestion with a bit of colour neg. When you say "until clear" do you mean until all the emulsion has stripped off or until it becomes opaque?