DPD powder

[waterbear]

I seem to remember reading on the old forum that if the DPD powder is light grey it is still ok to use but if it has turned dark it is no good. This is because it has become completely oxidized and had turned into a dye. DPD is an aniline dye precursor. When DPD oxidizes (from oxygen in the air, usually in the presence of moisture) it will turn dark. As an analogy, think of a bottle of hair dye. It starts out as almost colorless and when it is mixed with the peroxide it turns dark, hopefully after it has penetrated the hair. (I use this analogy because DPD IS one of the dye precursors used in permenant hair dye). It is still usable as long as it is not completely oxidized. You just might need to add more to develop the pink color. In this case chlorine is the oxidizing agent that is developing the dye (Wurster's dye which has a pink color). Just like a bottle of hair dye is usable as long as it has only darkened slightly and not turned completely dark. (I have been a licensed Barber and licensed Cosmetologists for 30 years now and have taught both professions in the past so I have some knowledge of this.)