protargol

[Edward Saiff]

Does anyone have experience using protargol (silver protein)?  I have 
been using it for about two years with excellent results.  The question I 
have has to do with how many times you can use the solutions involved 
before they loose their effectiveness.  Is there a way to test the 
protargol solution to see if it is usable without going through the 
process of staining some slides?