56 THE ESSEX NATURALIST.
in weight when immersed in water, and it is usual to endeavour
to coat the article—before immersion—with the thinnest possible
coating of wax. Briquetage does not readily lend itself to such
treatment, and an alternative method had to be devised.
The fragment (15 to 20 grms.) is weighed dry, and then
immersed in a bath of paraffin wax, kept just above its melting
point ; it is then removed, rapidly drained, cooled and re-
weighed. It is finally suspended by a thread in water and
rapidly reweighed.
The treatment with wax, thus applied, ensures that the
large internal pores are effectively sealed. As the fragment
cools, surface wax is sucked inwards and the thinnest possible
coat remains on the surface of the sherd. The figures thus
obtained have relative value and that is regarded as sufficient
for the purpose in hand.
The following example will serve as illustration:—
Rom : Brit: Rim. (Wt. taken 40.28 grms.)
After immersion in wax .. 41.58 grms.
Weight in water .. .. 19.82
Loss of Wt. .. .. 21.76
Whence, Apparent Density = 40.28
------- =1.85
21.76
The results are arranged in graphical form. The Graphs
show the apparent density of the various sherds, the average
density for each of the groups to which they belong and the
number of pieces in each group the apparent density of which
differs from the average figure by not more than 0.1, calculated
as a percentage of the total number of pieces concerned—the
figure thus obtained is termed the "Percentage Figure," or
"% Figure," for short.
It is conjectured that all the crude red ware was made
locally from "clay" dug on the sites, and that it was fired
in the "open" or in kilns temporarily erected and demolished
after each operation. The unusual porosity of the ware is
attributed to admixture of the raw material before firing with
chaff, straw, grass or other available vegetable matter. In