Finally I got an owl from Snape telling me the formula for this
developer!!! The old git asked 4 galleons for it!!! Anyway, here it is:
(actually it's a magically modified fine-grain developer)
Metol 2gr
Hydroquinone 12 gr
Sodium carbonate 7 gr
Sodium sulfite 50 gr
Potassium bromide 1 gr
water to 1 liter plus the magical part of the developer:
boil in 300 mls of water until turns purple:
lacewing flies
aconite
bubotuber pus
research is going in the Department of Mysteries on how to magically
develop colour film