Analog film photography and cameras

PMK is the name of the developer - it's also called PMK Pyro and it belongs to the family of pyrogallol developers. It's very toxic unfortunately. Pyrogallol developers are also known as "staining" developers and leave a deposit on the negative which tends to reduce the grain. The chemicals last for years in concentrate and you mix it up when ready to develop. After developing, stopping (must be non-acidic, eg. water) and fixing, you do an optional staining step which involves pouring the spent developer back in the tank and agitating as you would fixer. After that, there's the normal washing step. The 1:2:100 refers to the dilutions as PMK comes in two solutions which can only be mixed when ready to develop. So, 1 part solution A, 2 parts solution B and 100 parts filtered water.