212 Miscellaneous. [Aprit, 
all the moisture out of the ware; it is then exposed for twenty-four hours more to 
a heat as high as it can bear without fusion, which has the effect of baking the 
clay, of driving off the sulphur from the lead-ore, and of causing the oxide of lead 
to form a frit or imperfect glass with the clay, the other ingredient of the glaze. 
The fire is now fed with bavin-wood instead of coal, by which the heat is increased, 
the furnace is filled with flame, and the frit being converted into a perfect glass, 
flows uniformly over the surface of the ware. The fire is then allowed to go out, 
and when the furnace has become cool, the contents are removed. If the air has 
been still during the burning, and due care has been observed, the articles in every 
part of the kiln will be properly baked; but a high wind always renders the heat 
very unequal, so that the ware in the windward part of the kiln will not be baked 
enough, while that in the leeward part will be over-burnt and run to a slag. 
“ All articles of earthen-ware which after being baked are opaque, are more or less 
porous ; and if a heat somewhat approaching to their point of fusion, so as to ren- 
der them slightly translucent, cannot safely be applied, it is evident that such ware 
is not very proper for vessels employed in cookery, and for several other purposes, 
from the difficulty of keeping them clean, and from their liability to crack when set 
on the fire in a dampstate. In England, we endeavour to obviate this imperfection 
by means of a thick vitreous glaze; but as the ware itself is very fusible, the glaze 
must be still more so; and as oxide of lead forms the cheapest and most fusible 
glaze, this accordingly is the material universally employed by us. But there is a 
very serious objection to the use of this glaze, namely, that it is soluble in vinegar, 
in the juice of most fruits, especially when hot, and also in boiling fat; the conse- 
quence of which is, that the food of the lower classes, by whom alone cooking 
vessels of glazed red-ware are employed, is often contaminated with lead, so as seri- 
ously to impair their health by occasioning colics, and the other usual effects of lead 
poison. Possibly borax, which is now a cheap article and is very fusible, might be 
made to supersede the use of lead ; if not, the only way of avoiding this very seri- 
ous hazard to health, will be the use of more refractory clay, which, consequently, 
would allow the employment of a less fusible glaze free from lead. This has been 
done by Mr. Meigh, a potter in Staffordshire, to whom the Society awarded a me- 
dal for his invention ; the ware produced by him is far superior to that in common 
use, and well deserves the encouragement of the public. A species of ware, some- 
what superior to our common red-ware, is made at Lambeth, of Maidstone clay, 
being of a paler colour and a more compact texture than the latter, but does not 
take a uniform covering by the common glaze for red-ware ; it is therefore chiefly 
used for purposes which admit its employment in an unglazed state, or in situations 
where the imperfection of the glaze is not perceived, as in ornamented chimney-pots, 
gas-consumers, &c. 
‘* A more perfect, and indeed very excellent species of earthen-ware, is that called 
stone-ware, originally introduced from Holland, and now made in several parts of 
the kingdom, and especially at Lambeth. To one of the principal manufacturers of 
this ware, Mr. Wisker, I am indebted for the following particulars : 
‘‘ The materials are, pipe-clay from Dorsetshire and Devonshire, calcined and 
ground flint from Staffordshire, and sand from Woolwich and Charlton. 
** The clay is pulverized and sifted dry, andis either used alone, when an article of 
great compactness is required, as soda-water bottles, or is mixed with sand to 
diminish its contraction in the fire. For retorts and other large vessels, instead of 
sand, the refuse stone- ware, ground to a fine powder, is used. For the finer arti- 
