CHAPTER IX
COATED PAPERS AND BOARDS
Coated papers comprise those to which, after manufacture as paper, a mineral coating, white or coloured, is applied, in order to produce a smooth unbroken surface for the reception of fine printed work. Art, chromo, enamel, and surface-coloured papers are all coated after the body paper is made.
Art papers may be made of rag, esparto, chemical wood, or chemical and mechanical wood, or a mixture of any of the fibres. The body paper is carefully made, its ultimate state being kept in mind, and it is fairly well sized, but without a high glaze. The surface is kept so that the coating will cover properly and the adhesive be fully effective in holding the mineral. The operations comprise coating, drying, and finishing. The coating is carried out on a compact machine. A mixture of china clay, glue, and water is supplied at a constant level to the feed trough of the machine, from which it is transferred to paper by means of a roller and felt; oscillating and stationary brushes rub the coating into the paper, filling up all inequalities and leaving a smooth film on the surface. The purpose of the coating is to give a perfectly smooth surface, obliterating entirely the marks of the machine wire and felts, and to do this effectively the consistency of the mixture is regulated so that it may enter the minute depressions and deposit sufficient matter to take
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