Relief

(a) The degree of atmosphere or distance expressed in a photograph. (b) The height or the projection of a figure or feature from the ground or plane on which it is formed. Ex. The metallic silver image on the negative while still wet is in slight relief; i.e., the metallic image which forms a high-light is thicker than the gelatin in the transparent shadows.

Rembrandt Portrait

A portrait in which the greater portion of the face is in shadow; usually about one-fourth of the face is in light, while three-fourths is in shadow.

Repeating Back

(See Back, Repeating.)

Residues

Substances such as gold, silver and platinum which can be recovered from photographic wastes such as old toning baths, fixing baths, scraps of sensitized paper, etc. In small photog-graphic studios it does not pay to collect residues, but in large studios the residues are valuable.

Resin

Rosin. The residue left after distilling turpentine. Transparent amber-colored, hard, brittle, pulverizable resin; impure grades are darker, even almost black. Soluble in alcohol, ether, benzene, oils and alkalies, as well as acetic acid. Used in retouching medium.

Restrainer

A chemical which will check a developer or similar agent having too strong an energetic action. In the case of over-exposed negatives a 10% solution of potassium bromide is used in the developer. Water is one of the most valuable restraining agents.

Reticulation

(a) A fine net work of small lines on a surface of gelatin film plates and papers. Caused usually by too sudden a change in temperature of baths. (b) This defect is also noticeable on collodion films when dry. In this case it is due to the solvents employed in the manufacture of the collodion not having been sufficiently anhydrous, or it may be due to impure pyroxylin (gun cotton).

Retouching

The process of removing imperfections from negatives by means of a pencil. Also the improving of any defective parts which may be in either a portrait, landscape or commercial negative.

Retouching Desk

A desk or easel having an opening through which light is admitted, and on which the photographic negative is placed for retouching. The angle of the desk portion on which the negative rests is usually from 30o to 45o from the perpendicular.

Retouching Glass

A reading glass or magnifying glass employed to better examine the photographic negative while retouching.

Retouching Medium

The varnish or preparation applied to the negative previous to retouching, in order to give a tooth to the surface of the emulsion, to make the lead adhere.

Reversal

(a) The result of extreme over-exposure, which produces, on development, a positive image instead of a negative one. (b) The addition of thiocarbamides to the developer, such as hydroquinon or eikonogen, will restrain the action of the developer and result in a positive, instead of a negative, image being formed.