Methylene blue
Romanowsky-type stains can be made from either a combination of pure dyes, or from methylene blue that has been subject to oxidative demethylation, which results in the breakdown of methylene blue into multiple other stains, some of which are necessary to produce the Romanowsky effect. Methylene blue that has that has undergone this oxidative process is known as "polychromed methylene blue". Polychromed methylene blue may contain up to 11 dyes, including methylene blue, azure A, azure B, azure C, thionine, methylene violet Bernthesen, methyl thionoline and thionoline. The exact composition of polychromed methylene blue depends on the method used, and even batches of the stain from the same manufacturer may vary in composition.