Series editors' preface - Wood Tools

to reverse if necessary. Gelatin may not adhere
to a surface that has been treated with synthetics
in the past.
The application of wheat starch paste to
large areas is not advisable, even when a ‘dry’
solution is used. The paper lining is unlikely
to have been, and probably cannot be,
washed. As a result, moisture from the wheat
starch paste will bring some degradation
products present in the paper into solution. A
brown tide line will form as the solubilized
degradation products migrate and stain the
paper as it dries (Figure 15.2). In smaller
areas, ‘dry’ wheat starch paste can be applied
to a surface, and allowed to dry slightly before
pressure is applied. A heated spatula can be
used to speed drying. This is a very timeconsuming
process and may not be practicable
for securing large areas of a lifting paper
liner. The resultant bond between the wheat
starch paste, liner and wood substrate might
not be as strong as gelatin. The drying time
will be considerably longer than if gelatin or
Figure 15.2 An example of tide lining on a colour
lithograph entitled ‘The St Sebastian Society of Archers
at Bruges’. Water-soluble degradation products in the
paper move with water through the sheet. When the
water dries they are redeposited and form a brown tide
line. Once dry, tide lines can be permanently disfiguring
BEVA ® film had been used. Huxtable and
Webber (1986) give comprehensive directions
for preparing wheat starch paste. ‘Dry’ wheat
starch paste is prepared by placing a small
amount of paste onto blotting paper before
use to draw off excess moisture.
BEVA ® film can be used to secure a lifting
lining. The film is placed between the paper
and wood substrate and a heated spatula is
used to tack the lining into place. BEVA ® film
may not bond well or evenly to a wood
substrate because tacking takes place through
the drawer lining.
Synthetic adhesives may be appropriate if
gelatin is unsuccessful. A degree of flexibility is
necessary to accommodate the differential
expansion and contraction of the paper and
wood substrate. The adhesive chosen must be
flexible, with a glass transition temperature (Tg)
around room temperature. The flexibility of
thermoplastic polymers is affected by the
solvent in which they are dissolved (see section
12.4.3). Future removal of such adhesives may
be difficult in a small drawer interior. In
addition, solvent applied to remove the
adhesive may cause migration of the adhesive
into the paper and, by saturating the liner in
places, may cause tide lines or future oxidative
discoloration.
PVAC adhesives are not usually a good
choice for paper because their reversibility is
limited and the adhesive is stronger than the
paper. The reversibility of PVAC is limited
even in low concentrations. PVAC will swell
in polar solvents, such as acetone, but still
requires mechanical action for removal. The
paper substrate would typically fail before the
adhesive. In addition, it should be noted that
PVAC off-gasses acetic acid for up to a year
and the pH of many emulsions and dispersions
falls as they age (Down et al., 1996). As
a result many PVAC adhesives are not appropriate
for use with paper, particularly where
there is a risk that an acidic micro-climate will
form, e.g. a drawer interior.
15.3 Metals
Conserving other materials I 677
15.3.1 Introduction
The basic principles of metal conservation are to
preserve aesthetic value and historical and