The developing room must be a perfectly dark room, save for the light from a ruby- or orange-colored window (or combination of these two colors). Have plenty of pure running water and good ventilation.
Plates should always be kept in a dry room. The dark room is seldom a safe place for storage, because it is apt to be damp.
Various developing agents give different results. Pyrogallic acid in combination with carbonate of sodium or carbonate of potassium gives strong, vigorous negatives. Eikonogen and metol yield soft, delicate negatives. Hydrochinon added to eikonogen or metol produces more contrast or greater strength.
It is essential to have a bottle of bromide of potassium solution, 10 per cent, in the dark room. (One ounce of bromide of potassium, water to 10 ounces.) Overtimed plates may be much improved by adding a few drops of bromide solution to the developer as soon as the overtimed condition is apparent (a plate is overtimed when the image appears almost immediately, and then blackens all over).
Undertimed plates should be taken out of the developer and placed in a tray of water where no light can reach them. If the detail in the shadows begins to appear after half an hour or so, the plate can be replaced in the developer and development brought to a finish.
Quick development, with strong solutions, means a lack of gradation or half-tones.
A developer too warm or containing too much alkali (carbonate of sodium or potassium) will yield flat, foggy negatives.
A developer too cold is retarded in its action, and causes thin negatives.
Uniform temperature is necessary for uniform results.
If development is continued too long, the negative will be too dense.