Dissolve platina as for silver lustre. Let the solution fall into a large vessel of water at the temperature of blood-heat; the sal ammoniac must then be added, and the precipitate will immediately descend to the bottom of the vessel in an orange-colour powder; decant off the water, and repeatedly apply to the precipitate boiling water until the water becomes quite insipid; after being gradually dried it is then used for the purpose of producing a silver lustre in the following manner: - First, procure brown earthenware of a full soft glaze, and with a broad camel-hair pencil lay on all over the piece of ware the platina in solution, and fire it at a strong enamelling heat, by which it will acquire a shining steel-colour lustre; then take the platina oxide mixed up with water to a thickish consistence, and lay it on the steel lustre, and fire it again in a kiln or muffle, but not to exceed a blood-red heat; it is then called silver lustre, being less resplendent, having more solidity and whiteness, and a very similar appearance to silver.
On all white earthenware the platina in solution is perfectly sufficient to produce a silver lustre.
4 parts gold in solution, 1 tin in solution. Procure a vessel to contain 50 parts of water about the temperature of blood-heat, to be well mixed with the solution of gold, and then add the solution of tin by dropping it into the menstruum, at the same time constantly stirring it with a strong feather, which will produce a fine purple-colour liquor; but it will be necessary to add a few drops of the solution of silver, which will much assist to raise the colour and beauty of the purple; to help the precipitation of the gold from its solvent (provided the precipitation does not immediately take place) add a large proportion of boiling water or a small quantity of sal ammoniac, and a precipitate will instantly be procured; the clear liquor must then be decanted off, and the boiling water repeated until it is completely insipid. The residue consists of the oxides of gold, tin, and silver in combination, and is the only substance which has the property of communicating the purple colour to enamel glass; after the precipitate is prepared, the flux must be added; the proper quantity will solely depend on the fusibility or softness of the flux, and as the operation in a great measure depends on observation, a few experiments by the operator will be found useful.
To the purple precipitate may be added 30-45 enamel flux (c), according to the strength of colour intended to be made.
2 parts enamel purple, 3 manganese oxide, 12 enamel flux (c).
1 part green cop. peras calcined, 3 enamel flux (c). The greatest difficulty in preparing red is the calcination of the copperas; calcine the copperas in a vessel exposed to the heat of an open fire, by which means it will dissipate all its volatile contents, and leave a residue of iron oxide in powder; when it attains an orange or light red, the calcination is sufficiently accomplished; the residue is then washed repeatedly with boiling water, until the water becomes insipid and free from sulphuric acid.
1 part iron chromate, 3 1/2 enamel flux (d). This fine colour is produced from iron chromate, which has a greater affinity for lead than an alkali, consequently the flux prescribed is the only one which is susceptible of yielding its proper colour, as those fluxes which contain a large proportion of borax are very prejudicial, destroying the colour, and with the greatest difficulty forming any affinity at all, therefore should be avoided. The flux used should be highly calcined until it assumes a dark orange-coloured glass. Mix up with spirits of turpentine when dry.
3 dwt. gold in solution, 60 leaves book silver, 2 1/2 lb. enamel flux (a). Procure a vessel to contain 10 parts the quantity of hot water, then mix the water and gold together while the water is at the temperature of 190° F.; add pulverised sal ammoniac rather copiously, at the same time briskly stirring the mixture with a strong feather, until the appearance of a decomposition takes place, which will soon be observable by the gold being precipitated from the menstruum in the form of a tine yellow powder; when that is accomplished, let the vessel stand undisturbed a short time to allow the precipitate to subside, then decant the liquor off, and still add boiling water repeatedly to the precipitate until the water is perfectly insipid; in the next place put it on a plaster bat to dry, after which it must be mixed up with book silver and flux, according to the proportions given above, and well triturated in a mortar; then send it to the mill to be ground, when it will be in a proper state for use.
This colour is supposed to be best when of a purple tinge, which may be produced by merely calcining the preparation to the heat of ignition previous to being ground; if the colour be too dark, the mixture does not possess a sufficient quantity of silver; if it is too light, the silver must have been very plentifully added, therefore the operator must add or diminish accordingly. Great caution must be observed with this receipt, as the gold precipitated by the sal ammoniac will unite with it, and then has the property of fulminating; and when gently heated or smartly struck with any hard instrument will immediately detonate; this can only be obviated by a plentiful use of boiling water; a caution which ought to be strictly attended to, as it removes the dangerous quality by depriving the gold of its salt.
This is prepared by taking platina and dissolving it in aqua regia composed of equal parts of spirits of nitre and muriatic acid. The solution must be placed in a sand bath at a moderate temperature; then take 3 parts of the spirits of tar, and 1 part of the solution of platina, mixing the solution with the tar very gradually, for as soon as the combination takes place, an effervescence will arise, the nitrous acid will evaporate and leave the platina in combination with the tar. After the above process has been performed, should the menstruum be found too thin and incapable of using, set it on a sand bath as before for a few hours; the spirit of the tar will evaporate, and by that means a proper consistence will be obtained. It must be used with spirits of tar.
1 part nitric acid, and 3 of boiling water; add one-third of its weight of silver, dilute with five times its quantity of water, then add a portion of common salt, stirring it all the time; immediately a white precipitate will fall to the bottom of the vessel; the liquor must then be decanted off and boiling water repeatedlv added, until the water is quite insipid. This precipitate is the pure oxide of silver, and is the same as that used in the preparation of burnished gold.
2 parts nitrous acid, and 1 part muriatic acid, with an equal part of water; add granulated tin by small pieces at a time, so that one piece be dissolved before the next is added. This aqua regia will dissolve half its weight of tin; the solution when properly obtained is of a reddish brown or amber colour, but when gelatinous the solution is defective.
Take any given quantity of grain tin, and melt in an iron ladle; when in fusion, pour it into a vessel full of cold water, by which means the tin will be reduced into small grains or particles adhering to each other; then take a biscuit dish previously lined with flint, spread it slightly over with pounded nitre, take the granulated tin, and lay it on the dish 2 in. thick, adding a little more nitre on the top; 1 lb. nitre will be sufficient to oxidise 5 lb. granulated tin; the dish containing the tin and nitre is to be calcined in a reverberatory furnace or glazing oven; particular attention is required in seating it, so that plenty of room remains to admit a free access of air to pass over the metal, otherwise it is impossible to obtain the whole of it in an oxidised state.
These require the materials to be made very fine and calcined in air furnace, the heat at first to be generated very gradually; and when the whole mass is in a state of fusion increase the fire quickly, and there will soon be produced a fine white enamel; in the time of fusion it will be requisite to keep stirring the whole together with an iron spatula or rod.
3 1/2 parts flint, 3 calcined borax, 1 Cornish stone, 1/2 tin oxide.
8 parts flint glass, 2 red-lead, 1/2 nitre, 1/2 arsenic.
1 part Naples yellow, 2 enamel flux (a), 1 enamel flux (c).