POTTERY 621 



causing the colour to adhere firmly to the bisque surface, by which it is partially 

 imbibed ; it is then immersed in a tub of water, and the paper washed entirely away 

 with a sponge, the colour, from its adhesion to the ware, and being mixed with oil, 

 remaining unaffected. It is now necessary, prior to 'glazing,' to get rid of this oil, 

 which is done by submitting the ware to heat in what are called 'hardening kilns,' 

 sufficient to destroy it and leave the colour pure. This is a necessary process, as the 

 glaze, being mixed with water, would be rejected by the print, while the oil remained 

 In the colour. 



The printing under the earthenware-glaze is generally performed by means of cobalt, 

 and has different shades of blue according to the quantity of colouring-matter 

 employed. After having subjected this oxide to the processes requisite for its purifi- 

 cation, it is mixed with a certain quantity of ground flints and sulphate of baryta, 

 proportioned to the dilution of the shade. These materials are fritted and ground ; 

 but before they are used, they must be mixed with a flux consisting of equal parts by 

 weight of flint-glass and ground flints, which serves to fix the colour upon the biscuit, 

 so that the immersion in the glaze-liquor may not displace the lines printed on, as 

 also to aid in fluxing the cobalt. 



The ' bat-printing ' is done upon the glaze, and the engravings are for this style 

 exceedingly fine, and no greater depth is required than for ordinary book engravings. 

 The impression is not submitted to the heat necessary for that in the bisque, and the 

 medium of conveying it to the ware is also much purer. The copper-plate is first 

 charged with linseed oil, and cleaned off by hand, so that the engraved portion only 

 retains it. A preparation of glue being run upon flat dishes about a quarter of an inch 

 thick, is cut to the size required for the subject, and then pressed upon it, and being 

 immediately removed, draws on its surface the oil with which the engraving was 

 filled. The glue is then pressed upon the ware, with the oiled part next the glaze, 

 and being again removed, the design remains; though, being in a pure oil, scarcely 

 perceptible. Colour finely-ground is then dusted upon it with cotton wool, and a 

 sufficiency adhering to the oil leaves the impression perfect, and ready to be fired in 

 the enamel-kilns. 



The following are the processes usually practised in Staffordshire for printing under 

 the glaze : 



The cobalt, or whatever colour is employed, should be ground upon a porphyry 

 slab, with a varnish prepared as follows : A pint of linseed oil is to be boiled to 

 the consistence of thick honey, along with 4 ounces of rosin, half a pound of tar, 

 and half a pint of oil of amber. This is very tenacious, and can be used only 

 when liquefied by heat; which the printer effects by spreading it upon a hot cast- 

 iron plate. 



The printing plates are made of copper, engraved with pretty deep lines in the 

 common way. The printer, with a leathern muller, spreads upon the engraved plate, 

 previously heated, his colour, mixed up with the above oil varnish, and removes what 

 is superfluous with a pallet knife ; then cleans the plate with a dossil filled with bran 

 tapping, and wiping as if he were removing dust from it. This operation being 

 finished, he takes the paper intended to receive the impression, soaks it with soap- 

 water, and lays it moist upon the copper-plate. The soap makes the paper part more 

 readily from the copper, and the thick ink part more readily from the biscuit. The 

 copper-plate is now passed through the engraver's cylinder press, the proof-leaf is 

 lilted off and handed to the women, who cut it into detached pieces, which they apply 

 to the surface of the biscuit. The paper best fitted for this purpose is made entirely of 

 linen rags ; it is very thin, of a yellow colour, and unsized, like tissue blotting-paper. 



The earthenware biscuit never receives any preparation before being imprinted, the 

 oil of the colour being of such a nature as to fix the figures firmly. The printed 

 paper is pressed and rubbed on with a roll of flannel, about an inch and a half in 

 diameter, and 12 or 15 inches long, bound round with twine, like a roll of tobacco. 

 This is used as a burnisher, one end of it being rested against the shoulder, and the 

 other end being rubbed upon the paper ; by which means it transfers all the engraved 

 traces to the biscuit. The piece of biscuit is laid aside for a little, in order that the 

 colour may take fast hold ; it is then plunged into water, and the paper is washed 

 away with a sponge. 



When the paper is detached, the piece of ware is dipped into a caustic alkaline lye 

 to saponify the oil, after which it is immersed in the glaze-liquor, with which the 

 printed figures readily adhere. This process, which is easy to execute, and very 

 economical, is much preferable to the old plan of passing the biscuit into the mufflo 

 after it had been printed, for the purpose of fixing and volatilising the oils. When 

 the paper impression is applied to pieces of porcelain, they are heated before being 

 dippea in the water, because, being already semi-vitrified, the paper sticks more 

 closely to them than to the biscuit, and can be removed only by a hard brush. 



