Agriculture Reference
In-Depth Information
'Whitening' or 'whiting' is simply finely crushed chalk. The need for a shellac-
based medium, such as 'patent knotting', is emphasised by Richards (1901,
86-7) with regard to carved gauged work:
Gauged brickwork is a most admirable material for carving, the soft effect pro-
duced being quite equal to that of modelling.
The bricks, having been perfectly squared and the projection arranged, are set
in a mixture of dried or baked white lead and liquid shellac; being at the same
time rubbed together to form a tight joint. Carved brickwork may in this manner
be made to stand out in relief as much as 18"; but when this is the case the work
should be arranged from a model, the different projections being taken from this
and the work set accordingly…
White lead or whiting give body and pigment to the finished joint and appear
similar to one of lime putty and silver sand. Shellac sets hard, imparting
the desired strength to such a mix, being defined by Jennings and Rothery
(1936, 35):
Lac is a natural resin which exudes from a number of trees…. Stick lac is crude
resin. Seed lac is the first result of refining the crude resin. Shellac is the usual
commercial form; it is received in thin sheets…
Information provided by Hillary Miller, laboratory technician at Liberon
Waxes, indicates that commercially produced shellac really began in the
Victorian period as 'the industrial revolution of the early nineteenth century
ensured an increasing need for gum lac as a colouring dye and an adhesive'.
Bricklayers of this period were quick to realise the potential of shellac to
firmly unite their rubbing bricks. The occasional need to glue bricks together
led to the craft term of bricks being 'shellaced'. Where the glue joint between
bricks was not going to be seen, then just pure liquid shellac was used, in this
instance the method then was:
To shellac rubber bricks together, the liquid shellac is poured into water and
gently stirred about to remove the greater portion of the spirit [methylated]; the
shellac, very like curds in appearance, is then smeared upon the dusted surfaces
of two bricks, the latter rubbed together to make a tight joint, and left to set.
(Richards, 1901, 85)
For an ornamental 'blocked' keystone - of three or five voussoirs joined together -
the rubbers would be dusted, dampened, and then set with white lead or whit-
ing and shellac. These would be laid individually to the designed bond on
the bedding, or 'surfacing', slate and quickly tied-off with wire or string; with
appropriately placed thin timber 'packings' either side to protect the vulnera-
ble arrises. Once fully set and dry, the 'block', or 'lump' would be placed in the
