Reversed Negatives

(See Negatives, Reversed.)

Reversing Back

(See Back, Reversible.)

Revolving Back

(See Back, Revolving.)

Revolving Background

(See Background, Revolving.)

Rising and Falling Front

(See Front, Rising and Falling.)

Rives Paper

(See Paper, Rives.)

Rochelle Salts

KNaC4H4O6 + 4H2O. Potassium and Sodium Tartrate. Colorless, transparent crystals or white powder. Soluble in 1.4 parts water; less than 1 part boiling water; almost insoluble in alcohol. Used as a developer in the Kallitype process; also in the preparation of gelatino-chloride printing-out paper emulsions.


C6H7NO - II, 460; IX. Para-amidophenol. Crystalline powder. A one solution developer. Soluble in water and alcohol. Darkens on exposure to air. Use. Generally employed for developing rapid exposures. It is also an excellent developer for bromide papers; in fact, for all-around amateur use it is a very good form of developer to employ.

Roll Holder

(See Holder, Roll.)

Roller Squeegee

A wooden roller covered with rubber having a metal or wooden handle employed for mounting prints, etc. See Squeegee.)

Rontgen Rays

(See X-Ray Photography.)


(See Resin.)


An extremely fine mineral powder used for polishing metals, etc.

Rotating Stop

(See Diaphragm.)

R. R. Lens.

An abbreviation for rapid rectilinear lens.

Rubber Finger Tips

Finger stalls or caps made of rubber, to wear on the fingers when handling poisonous chemicals.

Ruby Glass

(See Glass, Ruby.)

Ruby Light

(See Light, Ruby.)

Ruby Varnish

(See Varnish, Ruby.)

Rust Spots

When iron is present in the wash water or in water used for compounding chemical solutions, rust spots will invariably occur when the iron comes in contact with the silver of the emulsion. Rust spots most generally occur on printing-out papers.

Safe Edge

A term generally used in carbon printing. A thin strip of black or non-actinic paper pasted around the edge of the negative. The safe edge may also be made of any opaquing material. The object of placing the safe edge around the negative is to keep the edges of the sensitive paper from printing. This is necessary in the carbon process, as the edges of the carbon print must be perfectly soluble; otherwise the carbon pigment would wrinkle and not adhere to the transfer support.

Sal Ammoniac

(See Ammonium Chloride.)

Salicylic Acid

(See Acid Salicylic.)

Common Salt

(See Sodium Chloride.)

Salted Paper

(See Paper, Salted.)


(See Potassium Nitrate.)


Any acid in which one or more atoms of hydrogen have been replaced with metallic atoms or basic radicals; any base in which the hydrogen atoms have been more or less replaced by non-metallic atoms or acid radicals; also, the product of the direct union of a metallic oxide and an anhydrid. The nomenclature of salts has a reference to the acids from which they are derived. Ex. Sulphates, nitrates, carbonates, etc., imply salts of sulphuric, nitric and carbonic acids. The termination -ate implies the maximum in the acids and the -ite the minimum. (Century Dictionary.)