A room from which all actinic light has been excluded and in which the sensitive plates and papers are handled during the process of changing, developing and printing. For ordinary plates and papers the ruby light is sufficient, but for color sensitive materials, almost total darkness is required. A green light, however, is employed for plates which are sensitive to red, etc.

Dark Slide

An English term for the plate-holder


The separation of a clear liquid from a precipitate deposit. Accomplished by gently inclining the graduate or allowing the liquid to run out without disturbing the precipitate at the bottom; also effected by means of a siphon.

Decilitre or Deciliter

A Metric measure of volume.

Decimetre or Decimeter

A Metric measure of length.

Decomposition of Light

(See Light, Decomposition of.)


An optical term meaning the defining power of a lens clearness and sharpness of image produced.


Rapid combustion.


An optical term meaning the bending of a ray of light toward the surface of an opaque body.


A Metric measure of weight.


A solid is said to deliquesce when it possesses the property of becoming soft or liquid by absorbing moisture from the air. Ex. Calcium Chloride.


Printing opacity of a negative.

Depth of Focus

(See Focus, Depth of.)

Depth of Printing

(See Printing, Depth of.)


A chemical term meaning that the substance is free from water, dry

Destructive Distillation

(See Distillation, Destructive.)


Sharply, clearly denned reproduction of an object. The use of small stops gives more detail to the image necessitates increased exposure.


A solution used to bring out and render visible the latent image in sensitive plates or papers.


The process of rendering an invisible latent image visible. Applied to any process and renders visible a photographic image.

Over Developing

1; II.

The carrying of development beyond the normal stage, producing too dense an image or silver deposit. An over-developed negative should be reduced. (See Reducer.)


An optical term denoting the change of the course of a ray of light when it is reflected or refracted from its direct course.


Whitish powder or transparent yellowish lumps. Soluble in water. Used as a substitute for gum arabic, also for making mountants.


A line drawn through the center of a circle terminating each way at the circumference. If the circumference of a circle is given and it is desired to find the diameter of it, divide the former by 3.1416, or multiply by .31831.