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rag content - 1. Paper that is made chiefly from linen or cotton fibers rather than from wood pulp, which is highly acidic. High rag content usually indicates a neutral pH. 2. A term that indicates the presence of cotton fibers in a sheet of paper. The content can vary from 25% to 100%.

rag paper - Cotton fiber paper. It is made from cotton cuttings and linters.

ragboard - Another name for museum board.

RC paper - Initials standing for resin coated. These papers are less expensive and easier to process and wash than paper gelatin silver bromide/chloride emulsions. Contemporary photographic color prints are made of resin coated paper.

ream - A standard parcel of paper, formerly twenty quires, or 480 sheets, now usually 500 sheets.

reducible sulfur - Naturally occurring element in paper and board stocks. Archival paper and board is process to minimize sulfur content.

relative humidity - The ration of the quantity of water vapor present in the air to the quantity which would saturate that air at any given temperature. The figure is arrived at by relating the amount of water vapor a special volume of cold air could support without reaching dew point at the given temperature to the amount it currently has. It is expressed: RH X/XXX x 100 = X%.

release paper - Usually silicon-treated sheet that repels adhesive. Used in dry mounting process. Release papers are characterized by smooth waxy surface, used also in bookbinding and other applications where adhesives are used.

restoration - The procedures that improve the condition of a damaged object and attempt to return it as closely as possible to its original condition.

reversibility - Ability to undo a process or treatment with no change to the object. Reversibility is an important goal of conservation treatment.

rice paper - A misnomer for paper made from the pith of a small tree found in the Far East. It is often, erroneously, called India Paper.

rice starch - Traditional starch used for mounting paste.

rosin - Solution obtained by cooking rosin with caustic soda ash. It is an additive which is used as an internal sizing for paper. Rosin sized paper is acidic and therefore undesirable for archival applications.

rubber cement - Adhesive consisting typically of a dispersion of vulcanized rubber in an organic solvent. Non-archival.