No light is perfectly safe or non-actinic, even that coming through a combined ruby and orange window or lamp. Therefore use great care in developing.

A light may be tested this way: Place a dry plate in the plate holder in total darkness, draw the slide sufficiently to expose one-half of the plate, and allow the light from the window or lamp, 12 to 18 inches distant, to fall on this exposed half for 3 or 4 minutes. Then develop the plate the usual length of time in total darkness. If the light is safe, there will be no darkening of the exposed part. If not safe, the remedy is obvious.

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 halftones.

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.

In warm weather, the developer should be diluted; in cold weather, it should be stronger.

The negative should not be exposed to white light until fixation is complete.

The negative should be left fully 5 minutes longer in the fixing bath than is necessary to dissolve out the white bromide of silver.

In hot weather a chrome alum fixing bath should be used to prevent frilling.

Always use a fresh hypo or fixing bath. Hypo is cheap.

Plates and plate holders must be kept free from dust, or pinholes will result.

After the negative is fixed, an hour's washing is none too much.

The plate should be dried quickly in warm weather else the film will become dense and coarse-grained.

Do not expect clean, faultless negatives to come out of dirty developing and fixing solutions and trays.