. I am still using my old grumbachers. 00000 or 5/0. I am careful with them so that must be why they are still in pretty good shape. But. I have been thinking of buying some backup brushes soon.
I originally was using plastic cheap disposable brushes but have moved over to the ZircoZhan natural brushes made for this purpose.
Something I originally did not know:
What ever brush you use, make sure it does not have a metal Ferrell holding the bristles as it reacts with the acid based stains and will effect consistency of your colors.