Open the book to the torn page. Repair small tears with archival document repair tape. Use as little as possible on the tear. Archival document repair tape usually does not adhere as well as using Japanese paper and a starch mixture.
Repair larger tears with Japanese paper and an adhesive, or methyl cellulose paste. Place wax paper between the page to be repaired and the next page. Tear a strip of Japanese paper along the grain about one-half inch thick.
Lay the Japanese strip over mylar and brush on the adhesive paste with a small brush. Lift the strip with tweezers and place it centered over the tear. Work the strip into a more centered position with a micro spatula or similar small device. Place another piece of wax paper over it.
Place a press board and weight over the mend. Keep in place and let dry for about an hour. Trim any excess Japanese paper from the page up to an eighth inch, then fold the small remaining excess under the page and paste.