5. The board was then developed by immersing in a basic and an acidic solution respectively. Two acids, ferric chloride (Eisen-3-Chlorid) and Sodium Persulfate (Natriumpersulfat - Feinätzkristall), can be used at this stage (etching) .This stage took at least 20 minutes. When etching is done the board changes from opaque pink to transparent yellow