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SEPTEMBER 10, 1880.] THE PHOTOGRAPHIC NEWS. 437 PHOTOGRAPHY AS A DECORATIVE ART. BY J. R. SAWYER.* Porcelain. The effect of the enormous heat to which the porcelain has been subjected for so long period has been to drive off every particle of moisture contained in the forms, which, by shrinking, now present themselves as having the accus tomed sizes and shapes; the action of the intense heat has also fused the various materials composing the dough or tenacious clay, out of which the articles have been pressed or moulded, into a vitreous and transparent substance, known as biscuit porcelain. The biscuit ware of Worcester is of a most lovely purity of colour ; not a trace of the grey tone observable in the clay state remains, but a pure unsullied white characterizes the pieces. The next step is to cover the absorbent ware with a non-absorbent film or glaze. It would appear that the biscuit stage of the manufacture would be the most suitable, photographically considered, for applying the decoration, but as a matter of fact, at present, the skill of the decorator is not brought into requisition until a later period, when the ware has received its glaze. The various pieces having been carefully taken from the seggars, and the powdered flint dusted from them, are carefully looked over, and all faulty specimens are put aside to be disposed of as wasters, and it is singular for what a very slight cause a piece is rejected. In most of the towns in the neighbourhood are earthenware shops where most lovely specimens, so slightly imperfect that their faults are non-apparent to the uninitiated, may be purchased for a few pence. The perfect pieces are now taken to the dipping room. Here the visitor sees large tubs filled with a creamy- looking fluid. At these tubs stand men, who take the biscuit ware, and, holding it with a dexterity acquired by practice, dip each piece in the fluid in such a manner that the glaze shall be perfectly distributed over the surface ; this is so cleverly managed that there is no trace on the finished article of the points where the articles have been held. From the dipping room they arc next taken to the drying stone, the heat of which rapidly dries the glaze. The dipped ware now goes into th trimming room, where it is carefully examined by women, who mend up any imperfect places, and otherwise make it perfect for the next operation, which is the firing, for the purpose of melting the glaze and causing it to cover the porcelain with that delicate bright enamel surface so characteristic of the Worcester manufacture. In the photographic decoration of porcelain the glaze has to be specially con sidered, as will be manifest when the mode of doing this has to be described. The glazes are of different degrees of hardness, varying with the practice of different manu facturers, and even with the different kinds of work turned out. Glaze is composed mainly of borax, calcined flints, and red lead, which, when fused by heat upon the surface of the porcelain, form a sort of glass. There is much secrecy about the composition of glazes, but the most easily fusible are said to contain more lead, whilst the most refractory contain a larger proportion of calcined flint. It will be seen presently, that in the applica tion of photography to the decoration of porcelain, it is almost impossible to use any but the pure colour, and to depend upon the fuzing of the glaze already upon the ware for the burning in and glazing of the photograph ; con sequently a glaze that fuzes at a comparatively low tempera ture should always be sought for. As the potter and the photographer have scarcely as yet begun to work in alliance with each other, this is a matter that at present causes difficulties which, when better understood, may notarise. To return to the dipped ware ; it has been dried, examined, and the perfect pieces are now ready for what is called the “ glost oven”; this is in reality a kiln very much like * Continued from page 430. the one previously described, and in which the pieces are placed separately, and with the utmost care ; the most extreme cleanliness is here a necessity, as particles of dust, or any foreign matter in fact, would settle upon the ware and spoil the result. The pieces being all placed and the oven filled, the door way is bricked up, the furnaces lighted. The whole is rendered incandescent by intense heat, and the operation is completed in about thirty-six hours ; at the expiration of this time the oven has probably cooled sufficiently to enable the porcelain to be removed, and it comes out perfectly glazed of a beautiful white colour, and is now ready to be decorated by the painter and gilder, and is in the state in which, for the present at any rate, it is available for the purposes of the photographer. In the decoration of porcelain, two distinct kinds of colour are employed, named respectively under-glaze and over-glaze colours; the former being supposed to be the oxides of various metals without addition, or with but a small addition, of the easily fusible substance known as flux, the latter being similar oxides with a considerable addition of this material. The writer 1 of this article has no actual knowledge of this branch of the business except what he has derived from his own experiments and observa tions, for the manufacture of porcelain colours is a trade in which the secrets are guarded with the most jealous care; the various makers are perpetually striving to out-do each other, and if a colour is invented of a new shade, or of a superior brilliancy, the mode of its production is kept absolutely secret. Fortunately, the decorative photographer needs only to work in monochrome, and provided he can obtain, or prepare, black, red, and blue, and manage to make them fuze at the same temperature, he has got over an initial difficulty ; but it is a difficulty. Suppose that the red vaporizes before the black is glazed, it simply flies off and leaves a cold black, where a rich warm brown is desired ; doubtless if the demand should ever become considerable, and the porcelain colour makers find it worth their while to understand the conditions of photographic decoration as applied to porcelain, the way will be immensely smoothed, but at present it is beset with pitfalls and difficulties in this direction. Assuming that a satisfactory colour has been obtained, the next question is how to apply it to the smooth, shining, and perfect surface presented by the porcelain. One method of doing this, and which has been already practised to some extent, is by the powder process. There are three formulae given in Mr. Solomon’s little work on Vitrified Photographs on Enamel, for a sensitive hygro- set pic compound, which, when poured upon glass and ex posed to light under a positive transparency, is hardened where the light penetrates, and becomes more or less sus ceptible to moisture according to the strength of the actinic rays acting through the various degrees of density in the transparency ; one of these compounds, composed (say) of dextrine, grape sugar, and gum-arabic, sensitized by bichromate of ammonia, is poured upon a clean glass plate and allowed to dry in the dark; when perfectly dry, this is exposed under a transparent positive in a printing frame to the action of the light; when sufficiently exposed, it is taken into a room lighted by yellow light, and the oxide colour, ground to an impalpable powder, is dusted upon the plate ; as the film attracts moisture gradually from the atmosphere the colour begins to adhere to the deep shadows, and finally the picture is developed in a colour that can be burned into porcelain or earthenware. The picture, having been developed, is coated with a thick collodion, which, when dry, holds the picture thoroughly ; the bichromate is removed by immersion in weak nitric or muriatic acid, which floats off the film from the glass, and it is now ready for the delicate operation of transferring to tho piece of which it is destined to form a portion as in destructible as the porcelain itself. (To be continued.)
