Page:Paper and Its Uses.djvu/85

Rh of the sheet may overcome the difficulty, or, if the size of the machine permits it, cutting the paper in half and rearranging the forme or other printing surface and putting on an extra feeder.

Art and other coated papers which have the coating fixed to the paper with glue in addition to the liability to wavy edges, may be troublesome by reason of the surface lifting or picking. The latter fault is caused by the coating being insecurely fastened to the body paper, the trouble being temporary or permanent. Storing the paper in a damp place will weaken the adhesive properties of the glue, and the coating will not stand the pull exerted by the printing surface, but will come away in places. The paper may be improved by suspending it to dry off the excess of moisture, but if heated air is used, the temperature should not exceed 90° Fahr. Newly coated papers may cause trouble, owing to the adhesive not being quite hard, and keeping in stock for a fair length of time, a month or two, may result in an entirely satisfactory issue. But if the papers must be used, maturing as already described, with a careful use of heat, will usually remove the trouble altogether. Slight modification of the ink may be necessary, and should be tried before condemning the paper altogether.

It will be found occasionally that the coating is not properly fixed to the paper, owing to insufficient glue, or a soft-sized body paper being used. Damp the thumb and press on the coated paper, lifting it a few seconds after. If a large part or the whole of the coating comes away the coating is at fault. Crumple a piece of the paper, treating it rather severely, and note the amount of coating which has left the paper when flattened out again. A large amount of dust indicates bad coating. Comparative tests should be