the really interesting thing I learn jim...
when I would tone one 7x17 with the 10 drops for 20mins. Then Id put another 7x17 VDB in toner bath. even after 20 mins. there seemed to be no discernable difference. SO I deduced, in my finite empirical science mind, that the pt had been completely replaced in the VDB. so it seemed a good economical and effective way to use just enough metal solution without wasting. hope that made sense.