THE "RED-HILLS" OF CANVEY ISLAND. 55
pans of determined form. Apart from "wedges" and a few
oblong blocks, supposed to be moulding tools, the crude red ware
may be arranged in three groups :—
(a) Small pans, relatively few in number and confined
for the most part to the May Avenue site.
(b) Pots definitely possessing the "briquetage" charac-
ter.
(c) Pots allied to (b) but thinner and less porous.
It is not always easy to distinguish between pottery of types
(b) and (c), but there are specific differences: (b) pottery is
definitely of "briquetage" type in the accepted meaning of the
term—coarse, hand-made ware manufactured locally and fired
in the "open" with large admixture of vegetable matter; it
is often coated with a thin layer of green glaze on the outer
surface, a layer which renders it less porous and which has helped
to preserve it; on the other hand, (c) pottery is thinner and less
porous and friable, and has probably been made locally and fired
in the "open" with less admixture of vegetable matter.6
The rims of both types are square-edged, but rims (c) are
often burnished, and, being less friable, are better preserved.
Perhaps one may define (b) pottery as "industrial" pottery,
used for evaporation of brine, and (c) pottery as "domestic"
pottery, made for household use.
"APPARENT DENSITY "OR "VOLUME WEIGHT" OF
POTTERY.
The origin of the Crude Red Ware found in the burnt earth
of the Canvey Red-Hill mounds is a matter of conjecture.
The distinctive character of the briquetage is its greater
porosity. A measure of the porosity of pottery is afforded
by a determination of what is called its "Apparent Density" or
"Volume Weight," and a study of the Apparent Density of the
cruder pottery was undertaken in the hope that the figures
might afford an aid to classification.
The term "Apparent Density" is employed to denote the
weight of a given volume of pottery, referred to the weight of an
equal volume of water, taken as unity. Pottery rapidly gains
6 A very interesting account of "Hand-made Pottery in Jutland," peat-fired in the "open,"
is given in Antiquity, June, 1940, p. 148.