Series editors' preface - Wood Tools

(a)
(b)
(c)
Figure 13.6 The use of grain filler. (a) Scanning
electron microscopy (SEM) photomicrographs of unfilled
and uncoated mahogany (Swietenia macrophylla): rough
areas are a result of poor preparation. (b) SEM
photomicrographs of unfilled and uncoated mahogany
(Swietenia macrophylla): this well-prepared surface will
take stain and varnish more evenly than that illustrated
in (a). (c) SEM photomicrograph of grain-filled
mahogany. The filler is a proprietary linseed oil-based
material
Conserving transparent coatings on wood 621
nineteenth and early twentieth century mahogany
furniture.
The method of application varies with the
filling material chosen. Paste fillers, proprietary
or home made, are applied using a coarse
cloth and working the filler first along the
grain, then across the grain. When the grain
has been filled, the bulk of the excess is
removed across the grain, because working
along the grain will simply dislodge the filler
from the wood pores. The filler should be left
until almost dry and then the surface wiped
along the grain with a lint-free rag, barely
moistened with solvent if necessary, to remove
the excess. Grain filler left on the surface will
obscure the figure of the wood. When the
filler is completely dry, the surface can be
lightly denibbed with 240 or 320 grit paper
and the surface is then ready for the next
finishing process.
Proprietary oil-based fillers offer as much as
30 minutes’ working time and may take one
or two days to fully set. They tend to saturate
the substrate but may be slow to cure and may
darken over time. Water-based fillers tend to
dry much more quickly and this can offer an
advantage for the integration of small repairs.
While acrylic fillers are likely to be more stable
and set quickly, their saturating properties may
be a little less satisfactory. Either type can be
effective and manufacturer’s instructions
should be followed. Proprietary fillers may be
purchased pre-coloured but may also be toned
with pigments. As with other colour matching
processes, it is helpful to use a test piece to
decide whether they are appropriate for colour
matching a given repair.
Dilute glue size has been used as a grain
filler in preparation for a varnish, and could
be pigmented to adjust the tone of the wood.
In some cases a small amount of a drying oil
was added to the size. Parchment size or
isinglass were recommended for the purpose.
Fiedler and Walch (1997) have observed different
fluorescence of such layers in comparison
to the hide/animal glue used as a wood glue.
When dry, the surface was worked with a
cabinetscraper or abrasive paper. The surface
could be treated this way two or three times.
When the grain had been filled and excess
removed, the surface was varnished.
Traditional oil-based recipes for grain fillers
include a mixture of linseed oil and dry