Ream

480 sheets of paper made up into 20 quires of 24 sheets each. The paper may be of any dimension.

Reaumur Thermometer

(See Thermometer, Reaumur.)

Re-Crystallize

To crystallize again.

Rectification

The act of removing impurities and to raise the strength of a substance by repeated distillation.

Rectified Spirit

Alcohol which is 95% pure.

Re-Development

A process of intensifying or altering the color of a silver image. The essential points of the process are, first, thorough washing of the print; second, bleaching the print; third, redeveloping.

Red Fog

(See Fog, Dichroic.)

Red Light

(See Light, Red.)

Red Prussiate of Potash

(See Potassium Ferricyanide.)

Reducer

(a) A solution used to reduce the density or contrast of a negative or print. (b) A term applied to the developer, owing to the fact that it chemically reduces the silver salts of the latent image to metallic silver.

Farmer's Reducer

A reducing solution originated by Farmer. Composed of solutions of potassium ferricyanide and sodium hyposulphite. (Formula given in text.)

Reducing

The process of reducing the density of negatives and prints by means of a reducer.

Reducing Agent

(a) A chemical which reduces a silver salt to metallic silver.

(b) A chemical which reduces the density of a negative.

Reduction

(a) Opposite to enlarging. The process of producing transparencies, prints or negatives from negatives, positives or prints of large size. (b) The process of reducing the density of a negative or print by means of a reducing solution. (c) The process of bringing out the latent image in a negative or print development

Reflecting Camera

(See Camera, Reflex.)

Reflecting Screen

(See Screen, Reflecting.)

Reflex Camera

(See Camera, Reflex.)

Refraction

The bending or changing of the direction of rays of light. Refraction takes place when the ray of light passes from one medium to another of different density or refractive power.

Refractive Index

Index of Refraction. The ratio between the sines of the angle of incidence and refraction, or a ray of light passing from one medium (usually the air) to another. Thus, this ratio for a ray passing from air into water is about 4:3, or, more exactly, 1.336, which is, therefore, the index of refraction of water.

(Century Dictionary.)

Register

(a) A sensitive plate is in perfect register when it occupies the same position as the ground-glass, when the image was sharply focused on it. (b) In printing from negatives we speak of the perfect register of the image on the print, then the partially printed image at all times coincides with the negative image. (c) The book used in the reception-room in the studio for keeping a record of sittings, etc.