twisting, and visible seams, and can manufacture thin pieces, as well as
pieces of large dimensions, of a purity of form that it is impossible to
obtain otherwise.

The method of moulding small objects has been described with sufficient
detail in technical works, but such is not the case with regard to large
ones, and for this reason it will be of interest to quote some practical
observations from a note that has been sent me by Mr. Constantine Renard,
who, for several years, has had the superintendence of the moulding rooms
of the Sevres works.

The process of moulding consists in pouring porcelain paste, thinned with
water, into very dry plaster moulds. This mixture gradually hardens
against the porous sides with which it is in contact, and, when the
thickness of the hardened layer is judged sufficient, the mould is emptied
by inverting it. The excess of the liquid paste is thus eliminated, while
the thicker parts remain adherent to the plaster. Shortly afterward, the
absorption of the water continuing, the paste so shrinks in drying as to
allow the object to detach itself from the mould. As may be seen, nothing
is simpler when it concerns pieces of small dimensions; but the same is
not the case when we have to mould a large one. In this case we cannot get
rid of the liquid paste by turning the mould upside down, because of the
latter's size, and, on another hand, it is necessary to take special
precautions against the subsidence of the paste. Recourse is therefore had
to another method. In the first place, an aperture is formed in the lower
part of the mould through which the liquid may flow at the desired moment.
Afterward, in order to prevent the solidified but still slightly soft
paste from settling under its own weight at this moment, it is supported
by directing a current of compressed air into the mould, or, through
atmospheric pressure, by forming a vacuum in the metallic jacket in which