Photographer's Formulary Hydroquinone is generally a clean-working and nonstaining developer. It oxidizes easily both in solution and as crystals.
At temperatures bellow 50°F/10°C hydroquinone developers are inactive. It is extremely susceptible to the action of bromide.
When compounded with alkali carbonates it gives a slow-working but contrasty developer.
With caustic soda (e.g., sodium hydroxide) its action is very rapid, with the highest possible contrast. For this reason, it is the most widely used developer for technical applications, especially in process work where the highest attainable contrast is essential.
In the presence of caustic alkali (i.e. high pH) it is not temperature-sensitive and can be used for low temperature developing.
Hydroquinone developers keep well and are slowly exhausted.
Hydroquinone alone is not largely used but in combination with metol (MQ) or Phenidone (PQ), it is among the most popular developers.
By varying the relative quantities of metol and hydroquinone and adjusting the quantities of sulfite and carbonate, almost any desired contrast or rate of development can be obtained.
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