Hydroquinone is a clean-working and non-staining compound typically found in most photographic developers. It oxidizes easily both in solution and as crystals. It's most common use is, along with Metol, to change the silver halides to elemental silver.
- At temperatures bellow 50°F/10°C hydroquinone developers are inactive. It is extremely susceptible to the action of bromide
- With caustic alkalies (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. When compounded with alkali carbonates it gives a slow-working but contrasty developer
- Hydroquione developers keep well and are slowly exhausted
- Hydroquione alone is not largely used but in combination with metol (MQ) or Pheinidone (PQ), it is among the most popular developers
- By varying the relative quantities of metol and hydroquione and adjusting the quantities of sulfite and carbonate, almost any desired contrast or rate of development can be obtained