Page 475 - Oriental Series Japan and China, Brinkly

MANUFACTURING PROCESSES

Sevres, for a long time back, the pegmatite of Saint
Yrieix is employed alone. If, in the factory's early
days, an artificial glaze was used, it was because the
potters were ignorant of the advantages to be derived
by employing the volcanic rocks of Haute-Vienne.

About the year 1780, the glaze was composed of a
mixture of twenty parts of sand from Fontainebleau,
twenty-four parts of porcelain stone, and six parts of
chalk. This composition, tolerably difficult to melt,
had disadvantages that led to its abandonment. At

any rate, it is with the processes now actually in use

that I compare those of China, and I believe myself

perfectly secure in the conclusions I record here. If

the addition of lime or of other matters to modify
the fusibility of the vitreous substances employed in

glazing porcelain, is exceptional in Europe, in China,
on the contrary, the use of pure petrosilex without

any admixture is confined to special cases. The

porcelains of China and Japan are generally covered
with composite glazes, obtained by mixing various
materials in proportions determined by the nature of

the ware. The substance which the Chinese add to

petrosilex to render the latter more fusible, is lime.
This is clearly shown both by the translation of Chi-
nese books, and by analyses which have been made
either of glazes taken from finished porcelains, or of
specimens sent by Pere Ly, marked ' lime ' by him,
and specified as part or the glazing material. I must

repeat that it is the lime alone which seems, in my

opinion, to play an active role in the calcined mixture
of fern-leaves and lime, having regard to the small
quantity of fern ashes that enter the mixture. For
the rest, these ashes contain only silica and insignifi-
cant quantities of phosphoric acid. I do not think

389