Book with wooden boards

Jack C. Thompson <tcl [at] teleport__com> writes

>On one side of the boards (generally the inside) I insert two or
>three (wooden) butterfly repairs, again, with hide glue.
>
>If the book is on the large side I'll also line it around with a
>strong handmade paper, using a mixture of hide glue and cooked wheat
>starch paste. I've e-mailed some JPEGs to Robert.

Depending on the size of board and the stress it will be exposed to,
a structural reinforcement of glue joints by means of butterfly
inserts might appear desirable.  In fact this only for peace of mind
of the conservator, but doesn't add to the stability of the object.

The animal glues recommended provide sufficient strength for joints
in boards with the described thickness. When exposed to extensive
lateral pressure, joint failure usually occurs in the timber to the
sides of the glue line. The paper lining Jack C. Thompson is
suggesting will give additional strength adequate for the context.
The paper needs to be applied to both faces of the board to avoid
cupping to one lined side.

It has been observed in a variation of applications in wooden
objects that butterfly inserts and surrounding areas are distorted,
that gaps have developed around the inserts and that they have
become detached or are even missing.  Butterfly keys have to be
inserted in perpendicular direction to the grain of the board to be
repaired. Both parts can be affected by compression set shrinkage as
result of the restriction of dimensional changes. These are caused
by fluctuations in the moisture content of the timber. Compression
set shrinkage will leave the key to be too small, and continued
movement and tension will cause the glue joint to fail.

A less interventive method such as  the dowels is preferable. Their
use will provide strength, and most importantly reduce the amount of
original material lost--even if the substrate was considered to be
of secondary significance. But that would be another topic to
discuss.

Henning Schulze
Programme Coordinator
BSc. Furniture Conservation Programme
Galway Mayo Institute of Technology
Letterfrack
County Galway
Ireland
+353 91 742668
Fax: +353 95 41 112


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                  Conservation DistList Instance 23:2
                  Distributed: Thursday, May 28, 2009
                        Message Id: cdl-23-2-004
                                  ***