Now, if we glance over the various materials that have entered into the composition of this very ‘artificial’ paste, we see that alumina, the substance which, together with silica, we regard as the essential element in all fictile materials, is present in very small quantities; what there is of it can only be derived from the marl and from the alum in the frit; and this inference is confirmed by an analysis made by Salvétat—he found, indeed, only 2·23 per cent. of this earth in a fragment of old Sèvres. It may safely be said that in no other fictile ware is so small a quantity of alumina present. With this poverty of alumina we may associate the want of plasticity—the extreme ‘shortness’ which distinguishes this clay, if clay it can be called. In order to throw it on the wheel it had to be worked up with a certain quantity of chimie, a mixture of black soap and fine glue; at a later time gum tragacanth was used. Most of the soft paste, indeed, was made in moulds, but even in this case the pâte chimisée had to be employed. It was not till a later time that these difficulties were in part overcome by the introduction of the English process of ‘casting.’
The kilns at this time were small, with only one hearth, in which poplar wood was burned, but the firing was sometimes continued for more than a hundred hours. Hellot tells us that after the first firing more than two-thirds of the charge had generally to be rejected. The remainder—the successful biscuitware—was now polished with grit-stone, before being dipped into the soup-like glaze slip: in the case of vessels of complicated outline, the glaze was painted on with a brush. This ‘enamel,’ as the French sometimes call it—the term must not be confused with our use of that word—was essentially a silicate of lead, soda, and potash—a flint or crystal glass, in fact, containing nearly 40 per cent. of litharge. Hellot describes its preparation as follows: the constituents of the glaze, thoroughly mingled together, were melted to a glass, which had then to be reduced to a fine powder, and mixed with water and vinegar to form the slip. The presence of vinegar hindered the deposition of the solid particles in the soup-like liquid, and at the same time promoted the adhesion of the slip to the surface of the biscuit. This biscuit, with its thick coating of glaze, was now again fired, this time at a more gentle temperature.
The plain white ware was now handed over to the painters and gilders, and it is at this stage that the advantage resulting from this thick coating of an easily fusible, lustrous glaze asserts itself. The pigments themselves, suspended in a flux of similar constitution, are at the temperature of the muffle-stove completely incorporated with the subjacent glaze, and do not, as in the case of the German and still more of the later Sèvres hard paste, lie as a dead coating on the surface.
Hellot gives in his report numerous recipes for these enamel colours—there are as many as twenty-five for the blacks alone—but from these empirical data little is to be learned. It would seem, however, that the ‘enamels of Venice,’ prepared doubtless by the Murano glassblowers, were imported for this purpose.
The muffle-firing was a long and complicated process—the preliminary heating in the case of large pieces occupied twenty-five hours. The superintendence of the firing of each batch was delegated to one of the painters—a most arduous and responsible task which often occupied as much as fifteen days, for each piece had to pass to a fresh position when a requisite degree of heat had been obtained.
The above summary will give some approximate idea of the complicated and delicate processes involved in the fabrication of the porcelaine de France at the time when the ware that is now most prized by collectors was being produced at the works. We must now give some account of the forerunners—the soft-paste porcelains made at Saint-Cloud and at Chantilly in the early part of the eighteenth century.
Saint-Cloud.—In 1695 the widow and children of Pierre Chicoineau (or Chicanaux) petitioned the king for the sole privilege of making the ‘véritable porcelaine de la même qualité, plus belle et aussi parfaite et propice aux mêmes usages que la porcelaine des Indes et de la Chine.’ In granting the petition, the rights of the Poterat family of Rouen are reserved; but it is stated that no porcelain had been made at Rouen for several years. The earliest description, curiously enough, of the manufacture of porcelain in France, is to be found in An Account of a Journey to Paris in the year 1698, by Dr. Martin Lister. In speaking of what he saw at the ‘potterie of Saint-Clou,’ Lister declares that the painting of the ware surpassed that of the Chinese, nor was the glaze inferior in whiteness and ‘smoothness of running without bubbles.... Again, the inward Substance and the Matter of the Pots was to me the very same, firm and hard as Marble, and the self-same grain, on this side vitrification. Further, the transparency of the Pots the very same.’ After more than twenty-five years of experiment it was only, says Dr. Lister, within the last three that the process had been brought to perfection. We may therefore place the beginning of the porcelain of Saint-Cloud about the year 1695.
PLATE XXXIII.
1—ROUEN, BLUE AND WHITE
2—SAINT-CLOUD, CELADON
3—SAINT-CLOUD, BLUE AND WHITE