244 THE ESSEX NATURALIST
If you have looked critically at bricks of a known date, handled
them, measured them and from them turned to consider dated
structures built of similar bricks, you will very soon acquire a
sense of period which has an immediacy far beyond the mere
remembrance of catalogued characteristics.
Plate 17 shows specimen bricks of almost all periods from Roman
times onwards, and all but one or two were made in Essex.
The Roman brick is large and heavy; 18in. x 12in. x 21/2in. thick
is a fair average for Roman wall bricks, although I have found
several bricks in the same Roman kiln at Colchester which varied
from 2in. to nearly 31/2in. in thickness, in the several specimens.
Any one brick was remarkably uniform throughout except per-
haps just at the margin which may be a little thicker. Holy Trinity,
Colchester, and indeed all the Colchester buildings prior to the
thirteenth century have much Roman brick incorporated. The
Roman hypercaust pillar brick was usually 9in. x 9in. and there
were several other standard sizes. Bricks made in segmental shape
were used for building pillars of circular section. These curved
forms will recur much later, in a quite different connection.
There is a great gap between the fourth century and the twelfth
century, in which we have no direct evidence of brickmaking in
Essex, or indeed elsewhere in England. I have read a reference to
Anglo-Saxon Chronicle 886, where bricks are alleged to be men-
tioned, but on reading the Parker Manuscript for that year, I find
no mention of bricks as such.
Before going on to deal with the bricks of post-Roman times, I
will take this opportunity to explain in outline how bricks are
made, because I am sure that some have only very vague and
floating ideas of what, in fact, determines the important charac-
teristics of Brick.
Firstly, the raw material is clay, natural clay, usually from
Eocene, sometimes from Jurassic deposits. Chemically the clay is
aluminium silicate, stained with some iron salts, impregnated with
sand and sometimes gravel, and with more or less organic im-
purity present. Often a clay containing, in addition, lime or chalk
is chosen for brickmaking and the colour of the finished brick will
depend upon the nature and proportion of these various admix-
tures and impurities, as well as on the firing temperature in the
kiln and the access of air during firing.
In the traditional methods of brickmaking the clay is dug and
broken up by weathering, for months at least, sometimes for years.
The weathered and puddled clay is shaped by one of several
processes which I will describe more fully later, and the now brick-
like shapes are dried slowly.
When sufficiently dry (and there is much craftsmanship in that
phrase "sufficiently dry") the bricks are stacked in a kiln and