624 POTTERY 



One per cent, of oxide of cobalt is added ; but one half, or even one quarter, of a 

 per cent, -would be sufficient to produce the fine Wedgwood blue, when the nickel 

 and manganese constitute 3 per cent., as well as the carbonate of iron. For the 

 blacks of this kind, some English manufacturers mix black oxide of manganese with 

 the black oxide of iron, or with ochre. Nickel and umber afford a fine brown. 

 Carbonate of iron, mixed with bole or terra di Sienna, gives a beautiful tint to the 

 paste ; as also manganese with cobalt, or cobalt with nickel. Antimony produces a 

 very fine colour when combined with the carbonate of iron in the proportion of 2 per 

 cent., along with the ingredients necessary to form the above-descrioed vitrifying paste. 



The following is another vitrifying paste, of a much softer nature than the preced- 

 ing : Felspar, 30 parts; sulphate of lime, 23; silex, 17; potter's clay, 15; kaolin 

 of Cornwall (china-clay), 15 ; sulphate of baryta, 10. 



These vitrifying pastes are very plastic, and may be worked with as much facility 

 as English pipe-clay. The round ware is usually turned upon the lathe. It may, 

 however, be moulded, as the oval pieces always are. The more delicate ornaments 

 are cast in hollow moulds of baked clay, by women and children, and applied with 

 remarkable dexterity upon the turned and moulded articles. The coloured pastes 

 have such an affinity for each other, that the detached ornaments may be applied not 

 only with a little gum-water upon the convex and concave forms, but they may be 

 made to adhere without experiencing the least cracking or chinks. The coloured 

 pastes receive only one fire, unless the inner surface is to be glazed ; but a gloss is 

 given to the outer surface. The enamel for the interior of the black Wedgwood 

 ware is composed of 6 parts of red lead, 1 of silex, and 2 ounces of manganese, when 

 the mixture is made in pounds' weight. 



The operation called smearing consists in giving an external lustre to the unglazed 

 semi-vitrified ware. The articles do not in this way receive any immersion, nor even 

 the aid of the brush or pencil of the artist ; but they require a second fire. The 

 saggers are coated with the salt-glaze already described. These cases, or saggers, 

 communicate by reverberation the lustre so remarkable on the surface of the English 

 stoneware, which one might suppose to be the result of the glaze-tub, or of the brush. 

 Occasionally also a very fusible composition is thrown upon the inner surface of the 

 muffle, and 5 or 6 pieces called refractories are set in the middle of it, coated with the 

 same composition. The intensity of the heat converts the flux into vapour ; a part of 

 this is condensed upon the surfaces of the contiguous articles, so as to give them the 

 desired brilliancy. 



Enamd-colaurs for painting on porcelain are metallic oxides incorporated with a 

 fusible flux. Gold, precipitated by tin, furnishes the crimson, rose, and purple ; oxides 

 of iron and chrome produce reds ; the same oxides yield black and brown, also 

 obtained from manganese and cobalt ; orange is from oxides of uranium, chromium, 

 antimony, and iron ; greens from oxides of chromium and copper ; blue from oxides of 

 cobalt and zinc. The fluxes are borax, flint, oxides of lead, &c. They are worked 

 in essential oils and turpentine, and a very great disadvantage under which the artist 

 labours, is that the tints upon the palette are in most cases different from those they 

 assume when they have undergone the necessary heat, which not only brings out the 

 true colour, but also, by partially softening the glaze and the flux, causes the colour 

 to become fixed to the ware. This disadvantage will be immediately apparent in the 

 case where a peculiar delicacy of tint is required, as in flesh-tones, for instance. But 

 the difficulty does not end here, for as a definite heat can alone give to a colour a per- 

 fect hue, and as the colour is continually varying with the different stages of graduated 

 heat, another risk is incurred ; that resulting from the liability of its receiving the 

 heat in a greater or less degree than is actually required, termed ' over-fired ' and 

 ' short-fired.' As an instance of its consequence, we cite rose-colour or crimson, 

 which when used by the painter is a dirty violet or drab ; during the process of firing 

 it gradually varies with the increase of heat from a brown to a dull reddish hue, and 

 from that progressively to its proper tint. But if by want of judgment or inattention 

 of the fireman the heat is allowed to exceed that point, the beauty and brilliancy of 

 the colour are destroyed beyond remedy, and it becomes a dull purple. On the other 

 hand, should the fire be too slack, the colour is presented in one of its intermediate 

 stages, as already described, but in this case extra heat will restore it. Nor must we 

 forget to allude to casualties of cracking and breaking in the kilns by the heat being 

 increased or withdrawn too suddenly, a risk to which the larger articles are peculiarly 

 liable. These vicissitudes render enamel-painting in its higher branches a most un- 

 satisfactory and disheartening study, and enhance the value of those productions which 

 are really successful and meritorious. 



In enamelling, ground-laying is the first process, in operating on all designs to 

 which it is applied ; it is extremely simple, requiring principally lightness and 

 delicacy of hand. A coat of boiled oil adapted to the purpose being laid upon the 



