I've been toning my Vandyke's with platinum. I mix up a litre of the toner at a time and then use it as a one shot. I've noticed a very slight tone to my highlights. It's almost barely there but it concerns me. I am trying to find the culprit and wondering if using toner which was made last summer might be at fault? I do remember reading somewhere that platinum toner does have a shelf life but what happens after that? Does is merely just loose strength or could it have a staining tendency.
The other possibility is that I'm not clearing the ferric iron completely. I am clearing from 10-12 minutes in citric acid bath ( 1 teaspoon per 2 litres), and then washing for an additional couple of minutes, before going into the toner.