Series editors' preface - Wood Tools

14.2.12 Yellow ochre
A coat of size pigmented with yellow ochre
was applied to a carved surface that was to
be gilded. This wash was intended to disguise
any recesses or undercutting that may be
inaccessible during gilding so that they would
not be noticeable. Traditionally, yellow ochre
mixed with size was used for this purpose but
modern gilders often omit this step and rely
on the yellow bole instead.
A stock preparation of yellow ochre may be
made by immersing some yellow ochre in
water so that, with time, the grit in the
pigment will sink to the bottom of the
container. The wet yellow ochre should be
taken from the top of this stock solution and
mixed with a pre-prepared 6–8% rabbit skin
size (15:1–12:1 v/v water:glue granules). Avoid
the sediment at the bottom because it is too
thick and may contain grit. The amount of
pigment used is not critical but should be
sufficient to colour the work in one application.
The size and yellow ochre mix should be
warmed in a double boiler and, if a large area
is to be covered, left in the double boiler to
ensure it remains hot. The yellow ochre and
size should be applied hot (around 55 °C) to
ensure that the colour reaches all the depths
of the carving and recutting. The yellow size
should flow on fluidly and easily and should
not need to be worked in with the brush. A
long-haired hog’s-hair brush large enough to
cover the work quickly should be used. Do
not expect the finished colour to be uniform;
overlaps in colour do not matter so long as
no ridges form. The colour should be more
concentrated in the depths and hollows of the
carving where it is needed most.
14.2.13 Bole
Bole is a coloured clay applied onto the gesso
before gold leaf is applied. The platelet structure
of the clay, in combination with the
cushioning effect of the underlying gesso
layers, allows the gold leaf laid over it to be
burnished to a high sheen. In addition, the
bole layer partly seals the gesso layer and
prevents free absorption of the size water into
the gesso layer below. The use and choice of
clay colour applied as a foundation for the
gold leaf has a great effect on the colour and
Introduction to traditional gilding 655
lustre of the finished work. Matching and
using the correct clay colours is of the utmost
importance, because the colour of the bole
will affect the final appearance of the gold. It
is essential that the gilder is aware of the
intended subtleties of semi-burnished, matte
and burnished areas before applying the clay.
Bole comes in many colours and is sold
either pre-mixed with water or, in a more
limited range of colours, in dry lumps or cone
form. Modern clays are manufactured from
kaolin (pipe clay) combined with a colouring
agent (usually ground earth pigments) and
water and may contain additives such as dyes,
lanolin or glycerine and preservatives (Thorn,
1987). Any grit in the bole will cause lumps
and scratch the gold leaf when it is being
burnished.
Many gilders prefer to use proprietary bole
that has been ground and pre-mixed with
water. Others prefer to start with the dry clays
or cones. A stock solution may be prepared
from dry clay or cones by grinding the clay
into very small particles using a mortar and
pestle and mixing with water to form a thick,
unctuous paste. The paste should be strained
once or twice through a fine nylon stocking
to remove grit and lumps, and placed in a
glass jar. This stock solution may then be used
in the same manner as proprietary wet clays.
Any clay has a limited shelf life once the glue
size has been added.
Colours in common use are yellow, red,
white, black and blue. Most traditional clay
colours can be achieved by blending these
basic colours and if necessary by adding a
small amount of an appropriate pigment.
Some pigments, such as terre verte, will give
a gritty finish and are therefore inappropriate.
Traditional bole varied in burnishing properties
depending on the colour. Yellow bole
burnished poorly and was used for the
background, red burnished well and was used
on highlights whilst Victorian black could be
highly burnished and was used on isolated
areas of highlighting. English clay could not
be burnished without the addition of graphite
and English burnish clay was made by mixing
equal parts of clay and mutton suet with a
small amount of graphite (Wetherall, 1992).
Bole may be prepared by warming enough
pre-prepared rabbit skin size to cover the
surface of the work three or four times. The