Watch tutorial about 5 methods to determine Paper grain direction https://www.youtube.com/watch?v=cO_HAeH7pGw
The grain direction always paralleled with the book spine For tears mending use Japanese tissue.
What is Japanese tissue?
A strong thin paper made from vegetable fibers. May be made from one of three plants: Kozo plant, Mitsumata, and Gampi tree.
The ink solubility tested, and I can use water-based adhesives such as CMC. Since the tear extends over text, the decision made to use 3.5 gsm, for the text legibility DON'T apply the adhesive OVER the tissue patch This wrong repair technique may end up resulting:
1 - A big patch of visible tissue
2 - Tideline in case of intensively applying water-based adhesive.
3 - Unwanted adhesive stains.
4 - Shiny surface appearance (If silicone paper used instead of Reemay) .
Apply a thin line of adhesive over the tear then place the tissue paper over the glued area. A weight is placed on top until the repair is dry. The tissue will be glued only on the edges of the irregular tear. Remove all the unglued extra tissue fibers, DON'T USE A sharp new blade during this process. Apply the adhesive over the Tissue edges. Moreover, the Polyester sheet acts as a barrier to avoid any excess from the adhesive. The Polyester sheet placed under the unglued tissue margin. The Reemay will Absorb any excess amount of adhesive.
What is Reemay? - Reemay is a non-woven polyester fabric. - It used as a support media for documents to be repaired, interleaving, or drying material.
Mend only one side of the sheet. For thicker paper, it would be better to mend both sides