Agriculture Reference
In-Depth Information
Figure 59
Baked and over-burnt
brick fresh from out of
a clamp firing in Boom,
near Antwerp, Belgium.
have been fired in the clamp or kiln using mainly wood or coal as fuel. The
advantage of timber has been discussed earlier with a lower overall tempera-
ture than coal, averaging 850-950ºC. This temperature is significant, because
at 900ºC vitrification begins to occur, and a fireskin develops on the brick face.
This prevents the brick performing as a rubber due to the increasing hardness
and mineralogical changes within the brick.
It has been repeatedly shown through chemical analysis of traditional rub-
bers that the best of them come from a top stratum of down-wash alluvial silt
and loam-like clean material. This has a naturally high silica content, such as
indicated in Lamb and Shepherd (1996, 68-70) (Table 1).
The results of chemical analysis carried out on samples of both standard face
bricks and augured brickearth taken from within the boundary of Aspley House
in Aspley Guise (Bedfordshire) (1692) were similar to the above general analy-
sis; in particular the high silica contents in excess of 80% (Table 2).
Geological tests carried out by Ceram Research on samples collected from
Aspley House, and the results analysed by the late Professor John Prentice, indi-
cated that the bricks had been made from the on-site brickearth (Prentice, 1996,
1-6). Furthermore, a print of a painting of Aspley House clearly shows how
it was left standing high upon the original ground level due to the surround-
ing excavation for brickearth to the front and sides of the property (Fig. 60).
Today this mound and depression have been subtly landscaped (Fig. 61).
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