This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Double Mounting. In double mounting it is often best to use two or more shades of the same color, showing as rules around the print, rather than to experiment with another color. Double mounting requires a good eye for color effects, and the more line effects used the narrower they should be. It is also important that the different papers of the mount be stuck together and quite dry, before the print is added, otherwise the print will cockle. A dab of paste on the top edge of each sheet will hold them together, and a narrow strip of paste along the top edge of the print will attach it firmly to the mount.
The whole thing, print and double mount, should be left under pressure for some hours.
Pasting. To come down to the dry details of pasting the print, use fresh starch paste, or Higgins' Photo Mounter, an excellent and ever ready preparation for ordinary mounting of prints. Good mountant must stick well and promptly; should not affect the print either chemically, mechanically, or by discoloration; must be easy to prepare and easy to use without cockling the mount. The paste should be applied with a flat bristle brush, using as little as necessary but applying it rapidly and evenly. Before the print has a chance to expand lay it on the mount, cover it with blotting paper and pass the squeegee roller over it lightly at first; then gradually with more pressure, make complete and uniform contact. The print will dry nearly flat if kept between blotters and under a heavy weight for a few days.