CHAP. IX.
Of the nature, preparation, and ufe, of the feveral fubftances employed in enamel painting.
SECT. I. Of general nature of enamel painting.
ENAMEL painting differs from all o-ther kinds, in employing, as a vehicle for the colours, (to hold the parts together, and. bind them to the ground they are laid upon) glafs or fome vitreous body; which be-ing mixt with the colours, and fufed or melt-ed by means of heat, becomes fluid; and having incorporated with the colours in that
ftate, forms together with them a hard mafs •when grown cold; and anfwers, therefore, the fame end in this, as oil, gum-water, fize, or varnifh, in the other kinds of painting.
The glafs or vitreous body, applied to this purpofe of mixing with the colours, in order to bind them to the grounds, is called a flux; and makes one principal clafs of the fubftances ufed in enamel painting, When this flux is ealily fufible, that is to fay, melts with a lefs degree of heat, it is, in the ftyle of thofe who work in enamel, faid to be SOFT, and when it is reluctant to melt, and requires a greater degree of heat, it is called HARD; and thefe terms are as well applied to the matter of the enamel grounds, and all other vitreous fubftances concerned, as to the fluxes. It is, in general, a perfection of, the flux to be (oft, or run eafily into fufion : but the great point, with refpeCt to this particular, is, that when feveral mixtures of colours and fluxes are ufed at the fame time, they fhould all correfpond to each other in the degree of this quality: otherwife fome would be rendered too fluid, and perhaps run the matter of the enamel ground into fufion, and mix with it, while others remained folid and infuffici- ently fufed themfelves. It is always necefla- ry, likewife, that the enamel of the ground fhould be confiderably harder than the mixtures for the colours: for if they both melt with the fame degree of heat, they will ne- ceflarily run together.
It being requifite that the body painted in enamel fhould undergo a heat fufficient to melt foft glafs, the matter of fuch body can only be gold, filver, copper, porcelain, or China-ware, hard glafs, and earthen-ware: and where the metals are ufed, if the painting be of the nature of a picture, or demand a variety of colours, it is neceflary that a ground of white, or fome other colour, fhould be laid on the metal; the body of which ground mufl neceflarily be of the fame vitreous. nature as the flux, but harder; as nothing elfe can endure fo great a heat that is capable of incorporating with, and binding the matter of the white, or other colour, to the furface of the metal. The grounds, therefore, make another principal clafs of the fubftances ufed in enamel painting.
The third clafs is the colours, which mull likewife be bodies capable of fuffering the heat of melted glafs: and fuch as will either them- felves be converted into glafs, or kindly incorporate with it in a melted Hate. This of courfe confines the matter of lixch colours to metals, earths, or other mineral bodies; all vegetable and animal fubftances being calcined and analyzed, with a greatly lefs degree of heat than the loweft fufficient to work enamel.
The fourth kind of fubftance is what I lhall call the fecondary vehicle; which is, fbme fluid body for laying on the ground, and working, with the pencil, the flux and colours when mixt together; fince, as they form only a dry powder, they could not be ufed as paint without feme fuch medium. But as this is to ferve only for fpreading and laying on the matter of the enamel, and not, like other vehicles, to aflift in holding the colours together, and binding them to the ground (that being in this kind of painting the office of the flux) it is neceflary, that it fhould be feme fuch fubftance as will evaporate and dry away without leaving any part behind: which would other- wife be heterogeneous matter with regard to the enamel: and confequently injurious to it.
Eflentialoils have been, therefore, uled for this purpole, as they have this quality of wholly drying away on the firft approach of heat, together with a flight unCtuofity, which renders, them capable of making the matter of the enamel work properly with the pencil.
The preparation of thefe feveral fubftances, have been till of. late greatly monopolized by the Venetians, except what were prepared at Drefden fince the eftablifliment of the China manufactures j or known but to few others, who praCtifed the preparing only fome kinds: and even at prefent, there are, perhaps, none in thus. country, who prepare more than a fmall part of the variety neceflary. For tho’ many poflefs the knowledge of fome particular articles, yet they are ignorant with regard to others, which are again, perhaps, known to thofe who are ignorant of thefe; there having been hitherto no means afforded to the praCticers of it of learning the particulars of this art in a . fyftem: and a deeper knowledge of the princi- pies and practice of chemiftry is requifite to the attaining it, without being taught, than could well fall to the fhare of painters, pr other artifts. I fhall, therefore, be more minute in my inftruCtions for the making the feveral kinds of «the grounds, fluxes, and colours j in order that they who are concerned in, or may be defirous to apply themfelves to the art of painting in enamel, which is now become the bafls of a confiderable manufacture in this Q.J. country,
country, may furnilh themfeives with whatever is neceflary in its greateft perfection.
Befides the knowledge of the preparation of the above fubflances, and of that part of the art of ufing them, which belongs to painting in general, there is another requifite, which is that of the burning,as it is called, the grounds, in
order to forming them on the body to be painted or enameled j as alfo the colours with the fluxes after they are laid on the grounds. What is mearit by BURNING, is the giving fuch a heat to the matter, when laid on the body to be painted, as will fufe or melt it j and confequently give to the flux or vitreous part of the compofition the proper qualities of a vehicle for binding the colours to the ground, and holding the parts together. As this requires a particular apparatus, I fhall endeavour to fhew the method of conftrtiding it in the moll expedite and eafy manner > and to give fuch cautions for the conduCt of the operation, both for burning the grounds and painting, as may bell enable thofe, who are lels experienced in it, to attain to perfection in this art. It cannot be expeCted, neverthe- lefs, confidering the nicety of the fubjeCt, fuch directions can be given, as will infure fuccefs in the firfl trials, with regard to feveral of the procefles; or even the general operations: but whoever will make themfeives mailers of the principles on which they depend, which are all along intimated, will ealily be able to corred their own errors.
A judgment formed by fome little experience, is likewife requifite for the preparing well the colours with certainty. For as different parcels of the fame fubftance vary frequently in their qualities, with regard to the degree or proportion, it is neceflary to make allowance accordingly in the proportion of the quantities in the mixtures; which cannot be done till fome little previous trial be made; and the power of judging of them be gained by an experimental acquaintance with them. But as the materials in general are very cheap, and the experiments may be made in die fame fire where aftual bufinefs is done, whoever would excel in the art of preparing and ufing enamels, fhould take a'confiderable fcope of experimental inquiry into the effect of all die various proportions and commixtures of the fubftances ufed.