Abstract: An on demand ink mixing system for a flexographic or similar printer utilizes a chambered doctor blade with a chamber divided by a flexible bladder to form ink chamber and a pressure chamber. Ink use is coordinated with print run length, and ink mixing and the collapse of the ink chamber to essentially zero volume are coordinated to coincide with the end of the run. The flexible bladder is also utilized in the operation of the ink cleaning system to move cleaning solution through all portions of the supply system and printer contaminated by ink mixed for the run.