Granite

Granite paper
A paper embodying very small coloured fibres
Graphite lines ...

Granite paper -- Not made of stone, but paper with colored fibers running through it.

Granite paper: A paper with small coloured fibres added during the production of the paper.
H
Hinge: Small pieces of glassine paper which are gummed on one side used in mounting stamps.

Granite Paper - Paper containing small colored fibers that is used to deter forgery.
Grade - A judgment of a stamp's level or range of imperfections.
Gravure - See "Photogravure." ...

Granite paper is rather unique. It looks like wove paper but has blue and red silk fibers throughout.
Perlure paper is very thin, not much thicker than an onion skin. It is usually hard and brittle.

Granite Paper of Switzerland SC#65 magnified 35x
Granite paper has colored (typically red and/or blue) silk fibers added to the furnish.

Papel con filametos: (Sp.) granite paper.
Papel Delmeina: (Sp.) paper, invented by a Belgian engineer, made in Spain and used for Civil War postal tax and charity issues; ...

Granite - paper containing countless very short hairs (fibres) of colour(s) contrasting with the main mat of the paper as a security against forgery.

Hence, we have "granite" paper and "silk" paper, both of which are made from paper in which small particles of silk thread are introduced into the pulp.

Other forms of paper used in stamp production are pelure, or semi-transparent paper; silk; granite; manila; ruled paper; and paper with moire overprint.

Papers commonly used in making postage stamps are rag paper, bond paper, blueprint paper, cardboard, cartridge paper, colored paper, enameled paper, prelure (semi-transparent paper), silk paper, granite paper, manila paper, and ruled paper.

The figures represent the hundreds of thousands of Canadians from all branches of the Service who were engaged in the First World War. The granite archway is surmounted by the bronze figures of Peace and Freedom, ...

See also: Stamp, Used, Perforation, Printing, Watermark