THE "RED-HILLS" OF CANVEY ISLAND. 59
The uniform character—judged by apparent density—of
the crude red ware is of interest in view of the primitive method
of manufacture employed. A similar uniformity is shown by
the stock bricks, fired in stacks, though the colour may vary
widely. Thus:—
Conditions of Firing. Colour. Apparent Density.
"Underfired" Pale brick red 1.68
" Overtired " (a) part of brick
yellow 1.61
(b) part black 1.66
Linear measurements show that the volume of the under-
fired and overtired products are practically the same, though the
underfired bricks contain undecomposed chalk, and it is usual
to retire them in a subsequent operation. It is concluded that
compensating factors are at work: expulsion of combined water
would be imperfect at lower temperatures, the honeycomb
structure of an overtired brick would tend to reduce the apparent
density and thus, in part, compensate for any increase due to
the deposition of fused matter or graphitic carbon in the pores.
The figures for Relative Volumes of Fired Products, given
in Column 3, ante, are calculated on the assumption that the
same weight of raw material, dried at 100°C, was used in all
the experiments. The volume of the corresponding fired
product was calculated from the loss of weight of the fired
product when immersed in water. Linear measurements confirm
these figures.
Dr. Lessing fired the pieces, they were prepared, and
examined after firing by myself.
KILN-FIRED POTTERY FROM THE CANVEY MOUNDS.
A great variety of Kiln-fired Romano-British pottery of the
ist and 2nd centuries A.D., was found associated with the
crude red ware in the burnt earth of the mounds. This pottery
appears to have been manufactured elsewhere and brought
on to the sites for domestic use. The apparent density was
determined for representative pieces of each class of ware.
Results are presented in graphical form, for comparison with the
corresponding figures for the cruder ware.