Use once a day for four to seven days. If pain is gone after four days, stop gentian violet. If better, but not gone after four days, continue for seven days. Stop after 7 days no matter what, not because it's dangerous, but if the gentian violet hasn't helped in 7 days, it probably won't. If not better at all after four days of use, stop the gentian violet, continue with the ointment as above and seek good help.
Gentian violet comes as a 1% solution in water. It also usually dissolved in 10% alcohol, as gentian violet is not soluble in pure water. This amount of alcohol is negligible, as the baby will only get a drop of gentian violet at each treatment. Apparently some pharmacists will dissolve it in glycerine instead of alcohol, if you wish.
Attention US residents: 2% gentian violet, which seems to be the usual concentration found in the US, should not be used. The pharmacist should dilute it to 1% for you.
If you are not getting better and/or you have pain in the breast as well that is not responding to treatment of the nipples alone:
If Still Not Getting Better at All…