In many books of the 13th-17th century wood is used to create a strong, solid cover. Mostly covered with leather these boards are often severely damaged. The main cause are insects...... Like in the example above, worms have eaten their way through (and through.....) the wood.
The result is a perforated board which has lost all of it's initial strength and purpose. Sometimes the loss of weight runs up to 60%. In these cases we usually replace the board. We use steamed beech-wood instead of the (mostly) originally used oak-wood. In (seeming) contrast to our restoration ethics we thus use another material then the original. The reason for this is that oak-wood emanates acids that affect the end-leaves as well as the cover-material.
When the board is though weakened by insects but not that severe we impregnate the boards with thinned animal-glue; in most cases this reinforces the wood sufficiently.
Cracks in the boards are (when possible) glued together with bone- or hide-glue. Missing corners and edges are mostly filled up with little pieces of contemporary wood, sometimes wooden or brass pins are added for extra strength.