SECTION IV.
Of the compounding and preparing the fluxes for enamel painting.
IN order to the underftandlng, and confe-quentlv managing more advantageoufly, the feveral compositions for fluxes, it will not be improper to inquire a little more particular-ly into the nature of the ingredients, and their operation on each other; as well as the pro- portion of power each has in producing its proper effedt: flnce by this means, the feveral mixtures may be better adapted to the pur- pofe, on each occafion, when their nature and degree of efficacy is well underftood, than they poffibly can by any particular recipes; though in order to give fuch an initiative knowledge of each particular, as may lead to proper experiments, I fhall fubjoin a complete fet, as well for the preparation of thefe, as the colours.
There are two kinds of fubftances infer the compofition of enamel fluxes. The one indued with a great propenfity to run into the vitreous fufion, or be converted into glafs : which is not meerly a paflive capacity of foon becoming glafs itfelf; but when become fo, of changing and affimilating other bodies commixt with it to its own vitreous nature. This kind confifts of falts, lead, and arfenic: but as falts, when vitrified alone, or with a fmali 2 proportion of other bodies, are (till liable to be diflolved by aqueous moifture, and as glafe under the fame circumftances, is extremely apt to fuller a corrofion by the air, and turn black and dull on its furfece,' it is necefiary to combine fome other bodies with them; which may counteract thefe bad tendencies; and render the compofition durable under all circumftances. Thefe corrective bodies of the proper matter of the flux, which therefore make the other kind of fubftapces enamel fluxes are compofed of, are calcined flints, fend, or fuch calcarious matter: which being perfectly white and refilling, in a vitreous ftate, the corroding or diflblving aCtion of all men* ftrua, give body and firmnefs to the fluxing composition without difcolouring, or any other way changing the proper fluxing ingredients ; except by weakning, in a certain degree, their vitrefaCtive power; and confequently rendering them fbmewhat weaker as fluxes, than they would be alone.
The moil aCtive flux amongfl- felts is borax: which, indeed, pofiefles this power in the greatefl degree hitherto known of any fimple whatever. The next is lead 4 which vitrifies with a very moderate degree of heat; and aflimilates to glais with itfelf, not only many kinds of earths, but all metals and femi- metals, except gold and filver in their intire ftate. Arfenic is the next powerful flux, or perhaps the moil; only it requires to be fixed by conjoining it with fome otner body already vitrified, otherwife it fublimes and flies away before it arrives at the vitrefadtive heat. The feveral kinds of other falts have the next degree of fluxing power j and among them fea fait pof- fefles the greateft: but they are not fufficiently ftrong themfelves to form an enamel flux fort enough to be ufed in painting: though as they are colourlefs, which is not the cafe of vitrified lead, they are very neceflary to be compounded with lead; or ufed in its place, aflifteef by borax, where abfence of every degree of colour is neceflary in the flux.
Of ihe general method of preparing faxes*
The method of preparing the feveral fluxes below given is the fame. The ingredients are to be well levigated with each other, on a porphyry ftone, with a muller of the fame matter, or of flint; or in a mortar of agate, of flint with an agate peftle : though where great quantities are to be prepared, a mortar and peftle of the common green glafs may be'pre- vioufly ufed.
Being levigated, the matter fhould be put into pots of a proper fize, made of the fub- ftances, and in the manner, directed p. 240 ; and placed in a furnace where the heat is nearly that of a ftrong culinary fire: for though a greater heat accelerates the vitrification, yet it renders the compofition harder, that is, weakens its fluxing power. When the vitrification is perfedt, which muft be known by the matter’s becoming tranfparent, and fre6 from air bubbles, it muft be taken from the fire ; and poured out on an iron plate clear of any ruft : and then, being powdered when cold, if the operation appear to have fucceeded, ic mufl be kept for ufe ; but, if any turbidnefs or foul- nefs appear in particular parts, fuch parts Ihould be picked out; or, if the whole be depraved with fpecks or cloudy, it fliould be again powdered and fufed j and then treated in the fame manner as at firfi:.
- Of glafs of lead.
Simple glafs of lead, though a-foft flux, is not proper to be ufed alone: for the air, as was before mentioned, corroding it, a cloudinefs or fkim is apt to come on the furface; which gives a dulnefs and unpleafing appearance to the enamel; and fometimes fouls the brighter colours. As it forms, however, in a more compound ftate, one of the beft fluxes, the preparation of it Ample is neceflary to be known: for though the ingredients which compofe it might be fluxed together with the other ingredients of the fluxes and colours j yet it is better to vitrify it feparately firfi:, and confequently purify it from thofe feculenciesanddrofs, whicn are apt to be formed in the firfi: fufion. The manner of preparing, glafs of lead, fuch as is to be underflood to be meant in the fucceeding recipes, is as follows.
“'Take of red lead two pounds, of flints rt calcined and levigated as above directed ** p. 247, or, in default of flints, of white “ land ground to fine powder, one pound: “ vitrify and prepare them according to the “ general directions before given."
Compojition of a flux, for common , moderately foft.
N° 1.
<x Take of the glafs of lead one pound, of ** pearl alhes fix ounces, of fea fait two ounces. ** Treat them according to the general direc- “ tions for fluxes.”
This is a very cheap flux; and will ferve extremely well for all purpofes where a tinge of yellow will not be injurious; or where tne flux is not required to be extremely foft.
Compoftion of a foftflux for common purpofes.
N° 2.
** Take of the glafs of lead one pound, of ,c pearl alhes fix ounces, of borax four ounces, ** of arfenic one ounce. Proceed according to f( the general directions.”
This is a very foft flux; and will vitrify a very large proportion of zaffer, or the precipitated powders, or calxes of metals. It is, therefore, very proper for forming ftrong glazing ; T 2 colours,where harder fluxes are ufed with the reft: or for all purpofes, where there is any neceflity for, or convenience in, burning the enamel with a {lighter heat.
Compojition of a tranjparenfflux, perfe&ly white, and moderately foft.
' N° 3.
tc Take of common flint glafs powdered “ one pound, of pearl alhes fix ounces, of fea “ fait two ounces, of borax one ounce. Pro-“ ceed as with the others.”
This is proper for purples, crimfons, and fuch colours as are injured by any tinge of yel-low; as alfo for white, where purity is re-quired. It is rather harder than N° 1 above
given ; but that may be corrected where ne-ceflary by any intermediate proportion of bo-rax, betwixt that given here and in the next.
of a tranfparent flux perfectly white, and very foft.
N° 4.
“ Take of common flint glals powdered “ one pound, of pearl afties and borax each “ four ounces of common {alt and arfenic each “ two ounces. Mix, and flux them according“ to die general directions: but they muft re-“ main in fufion longer, if any doud&nefo ap-pear in confequence of the arfèflifc; which ** though indued with a flrong fluxing poWfcr, ** when in a vitreous hate, does Hot neverthe- ** lefs vitrify, when the proportion is large “ with refpedt to the other ingredients, fo “ quickly as they do; but gives a milky tur- <( bidnefs to the glafs, till its own vitrification 4‘ be perfect.”
This is a very foft dux; and prefer in all cafes, where fuch is necefiary, and the yellow tinge of the common foft flux above given would be detrimental. But the proportion of borax or arfenic may be varied as is above intimated, either in this, or any of the other compofitions; or the arfenic, and fea fait, omitted according to the occafion: but thé proportions of the other ingredients fhould be adhered to j becaufe they are fuch as are moll advantageous with refpedt to the relations thé qualities of each have to the others, and to thé general intention. -
Of the white Venetian , as a flux.
The principles on which fluxes are formed, and the nature of the fubftances proper to form diem, having been very little underftood, of indeed known, and the compofitions of the fluxes ufed having been kept fecret at Venice, and Drefden, or by the few elfewhere who have learnt them,, it has been almoft univer- fally pradtifed to ufe the white Venetian glafs as a flux: butit has not, that 1 know of, been lately imported into this country, or any where regularly fold for this purpofe j but obtained, by thofe who ufe it, by feeking out drinking glafles, fmail vafes, or other fuch wrought pieces: and indeed I am in fome doubt, whether the fame glafs be now made at Venice, or any where : but that what is found is the remains of a kind formerly made, and difperfed all over Europe, while the Venetians had the the monopoly of fuch fort of manufactures wholly in their hands. This glafs is of a moderate foftnefs; and agrees very well with the colours in general: but having a milky turbidnefs mult certainly be lefs advantageous to the tranfparent or glazing colours than a flux perfectly pellucid. The compofition . of this glafs is not known atprefent to any here} for all the kinds defcribed by Neri feem much harder than this j though, as he gave all the compofitions then in ufe in Italy, and particularly underftood the Venetian manufacture, one might have expeCted he would have taken it in, as it mull have been made in very large quantities from the copious remains of it we find in every part of Europe. This glafs may be known, from any common kind,..by its having a milky turbidnefs; by which it may be diftinguifhed from all tranlparent forts ; and by its yet coming much nearer to tran- fparency, than any of the white opake- kinds made at prefent.