POTTERY 623 



the mixture begins to boil; it is then cooled, by setting the vessel in cold water; 

 after which it is stirred afresh, and strained through linen. The above ingredients, 

 after being well mixed, are to be allowed to settle for a few minutes ; then the re- 

 mainder of the solution of gold is to be poured in, and the whole is to be triturated till 

 the mass has assumed such a consistence that the pestle will stand upright in it ; 

 lastly, there must be added to the mixture 30 grains of oil of turpentine, which being 

 ground in, the gold lustre is ready to be applied. If the lustre is too light or pale, 

 more gold must be added, and if it have not a sufficiently violet or purple tint, more 

 tin must be iised. 



Platina lustre. Of this there are two kinds : one similar to polished steel, another 

 lighter and of a silver-white hue. To give earthenware the steel colour with platina, 

 this metal must be dissolved in aqua regia composed of 2 parts of muriatic acid and 

 1 part of nitric. The solution being cooled, and poured into a capsule, there must 

 be added to it, drop by drop, with continual stirring with a glass rod, a spirit of tar, 

 composed of equal parts of tar and sulphur boiled in linseed oil and filtered. If the 

 platina-solution be too strong, more spirit of tar must be added to it ; but if too weak, 

 it must be concentrated by boiling. Thus being brought to the proper pitch, the 

 mixture may be spread over the piece, which being put into the muffle, will take tho 

 aspect of steel. 



The preparation of platinum, by means of which the silver lustre is given to earthen- 

 ware, is prepared as follows: After having dissolved to saturation the metal in aqua 

 regia, composed of equal parts of nitric and muriatic acid, the solution is to be poured 

 into a quantity of boiling water. At the same time, a capsule, containing solution of 

 sal-ammoniac, is placed upon a sand-bath, and the platinum-solution being poured into 

 it, the metal will fall down in the form of a yellow precipitate, which is to be 

 washed with cold water till it is perfectly edulcorated, then dried, and put up for use. 



This metallic lustre is applied very smoothly by means of a flat camel's-hair brush. 

 It is then to be passed tkrongh the muffle-kiln ; but it requires a second application 

 of the platinum to have a sufficient body of lustre. The articles sometimes come 

 black out of the kiln, but they get their lustre by being rubbed with cotton. 



Dead silver on porcelain is much more easily affected by fuliginous vapours than 

 burnished. It may, however, by the following process, be completely protected. 

 The silver must be dissolved in very dilute acid, and slowly precipitated ; and the 

 metallic precipitate well washed. The silver is then laid (in wavy lines?) upon the 

 porcelain before being coloured (or if coloured, the colour must not be any prepara- 

 tion of gold) in a pasty state and left for 24 hours, at the expiration of which time the 

 gold is to bo laid on and the article placed in a moderate heat. The layer of gold 

 must be very thin, .and laid on with a brush over the silver before firing it; when, by 

 the aid of a flux and a cherry-red heat, the two metals are fixed on the porcelain. 



An iron lustre is obtained by dissolving a bit of steel or iron in muriatic acid, mix- 

 ing the solution with the spirit of tar, and applying it to the surface of the ware. 



Aventurine glaze. Mix a certain quantity of silver-leaf with the above-described 

 soft glaze, and grind the mixture along with some honey and boiling water, till tho 

 metal assume the appearance of fine particles of sand. The glaze being naturally of a 

 yellowish hue, gives a golden tint to the small fragments of silver disseminated 

 through it. Molybdena may also be applied to produce the aventurine aspect. 



The granite-like gold lustre is produced by throwing lightly with a brush a few 

 drops of oil of turpentine upon the goods already covered with the preparation for 

 gold lustre. These cause it to separate and appear in particles resembling the surface 

 of granite. When marbling is to be given to earthenware, the lustres of gold, platinum, 

 and iron are used at once, which, blending in the fusion, form veins like those of marble. 



Of late years a beautiful lustre has been given to porcelain by a process patented 

 in 1857 by Messrs. Gillet and Brianchon, of Paris, and largely used at the works of 

 Worcester and Belleek. The effect is obtained by using nitrate of bismuth as a flux 

 to the metallic oxides which give colour, and by employing oil of lavender as a 

 vehicle. (Spec. Patent, No. 1896, July 8, 1857.) 



Pottery and ware of the Wedgwood type. This is a kind of semi-vitrified ware, 

 called dry bodies, which is not susceptible of receiving a superficial glaze. This 

 pottery is composed in two ways : the first is with barytic earths, which act as fluxes 

 tipon the clays, and form enamels : thus the Wedgwood jasper-ware is made. 



The white vitrifying pastes, fit for receiving all sorts of metallic colours, are com- 

 posed of 47 parts of sulphate of baryta, 15 of felspar, 26 of Devonshire clay, 6 of 

 sulphate of lime, 15 of flints, and 10 of sulphate of strontia. This composition is 

 capable of receiving the tints of the metallic oxides and of the ochreous metallic earths. 

 Manganese produces the dark purple colour ; gold, precipitated by tin, a rose colour ; 

 antimony, orange ; cobalt, different shades of blue ; copper is employed for the browns 

 and the dead-leaf greens ; nickel gives, with potash, greenish colours. 



