" We again repeat, that it is much to be desired that so curious an art should not be lost to France; and the committee of chemical arts, in order to for ward this object, have charged me to propose, that Nobili be recompensed for his interesting com munication, by inserting this report in the Bulletin of the society." The following Letter on ornamenting Steel with Gold and Platioa was addressed to the Editor of the Tech nical Repository.
Bridge Cottage, Camberwell, Jan. stir, 1826.
Siu,—In a paper inserted in your Repository for NoVember last. I suggested some inquiries respecting the various methods of gilding practised by artizans. Since that period, I have been prosecuting some ex periments with success, for ascertaining the proper mode of superficial gilding upon steel; and I trans mit the result to you, for the benefit of that class of artists. It is necessary, perhaps, to premise, that the instructions gil:en, in most elementary works upon chemistry, for gilding with the ethereal solution of gold, are either erroneous, or not sufficiently explicit; and to this cause may be traced the many failures which have occurred in practising this art.
The following is the process which I used; and which answers equally well, either for gold or platina.
Dissolve any quantity of gold or platina in nitro muriatic acid (aqua reeia), until no further efferves cence is occasioned by the application of heat. Eva porate the solution of gold or platina, thus formed, to dryness, in a gentle heat (it will then be freed from all excess of achi. which is essential); and re-dissolve the dry mass in as little water as possible: next take an instrument which is used Icy chemists for dropping liquids. known by the name of a separating-funnel, having a pear-shaped body, tapering, to a line point, and a neck capable of being stopped with the finger or a cork; which may contain a liquid ounce, or more: fill it with the liquid about one quarter part; and the other three parts must be filled with the very best sulphuric ether. If this be rightly managed, the two liquids will not mix. Then place the tube in a horizontal position, and gently turn it round with the finger and thumb. The ether will very soon be im pregnated with the platina or gold, which may be known by its change of colour. Replace it in a per
pendicular position; and let it rest for twenty-four hours; having first stopped the upper orifice with a small cork. The liquid will then be divided into two parts; the darkest coloured being underneath. To separate them, take out the cork, and let the dark liquid flow out: when it has disappeared, stop the tube immediately with the cork; and what remains in the tube is fit for use, and may be called the gilding liquid. Let it be put into a bottle, and tightly cork ed. When an article is to be gilded, a vessel of glass or unglazed ware must be provided, of just sufficient size to admit the article: it must then be filled with the gilding-liquid, nearly to the top. The steel must be very highly polished, and be entirely free from rust or grease. .1 basin, full of clean water, must be ready at hand: the article must be immersed into the gild ing-liquid, and allowed to remain as short a time as possible; then be taken out, quickly plunged into wa ter, and well rinsed: it must next be dried with blott ing-paper, and be placed in a temperature of 150° Valli.. till it be completely heated throughout; it may then be polished with rouge and a soft leather; or, which is better, be burnished.
It will be as well to observe, perhaps, that the mu riate of gold or platina, formed by digesting these metals in nitro-muriatic acid, must be entirely free from all excess of acid; because it will otherwise act too forcibly on the steel, and cause the coating of gold to peel off. Pure gold must he employed. The ether must not be shaken with the muriate of gold, as is advised in chemical publications, for it will be sure, then, to contain acid: but, if the two liquids be continually brought into contact, by the motion I have described, the affinity between ether and gold is so strong, as to overcome the obstacle of gravity, and it will hold the gold in solution. The etherial solu tion may also be concentrated by gentle evaporation. Care must be taken not to wipe the steel until the heat has been applied. This gilding is an effectual protection against rust; and is, at the same time, very ornamental.