SECTION V.
Of the compofition, preparation of white enaihel for , and other ■ .purpofes.
Compofition of common, white enamel of moderate hardnefs.
“ f ■ ' A K E of glafs of lead one pound, “ it of pearl afhes and calx of tin- each “ half a pound.. The ingredients being tho- “ roughly mixt, by grinding them together on “ a porphyry ftone, or by pounding and rub- “ bing them well in a glafs mortar, put them ■** into a proper melting pot; and give them a mo“ derate heat, till they incorporate thoroughly : ** but the fufion fhould not be either ftrong, “ or long continued; for, if the glafs be per“ fectly liquified, the calx of tin is apt to fub- “ fide; and, confequently, to be unequally mixt “ in the mafs when cold. When the heat has “ had its due effect, take the pot out of the “ fire ; and pour the matter on a clean iron * ‘ plate; or into molds to form it into cakes, like “ the Venetian enamel, if it be fo defired.” This is fofter than the common white glafs, and about the degree of the common Venetian enamel. It is not very white, nor confequently fit for dial-plates, or other purpofes where the cleamefs of colour is required: but for paintings where it will be covered, or where pure white is not neceflary, it will extremely well anfwer all purposes.
Compojition of a veryfoft white enamel for mon purp
N° 2. ’
“ Take of glafs of lead one pound, of pearl “ alhes and calx of tin each half a pound, of “ borax and common fait each two ounces, and “ of arfenic one ounce. Treat them as the fore- 5‘ going: but be very fparing of the heat; and “ take the matter out of the fire as fopn as it “ forms one homogeneous mafs, without fuf- ** fering it to fufe till it be perfectly fluid.”
This is very foft; and will fcarcely admit, if ufed as a ground, the fluxing of colours upon it without running into fufion itfelf with the fame heat; and, confequently, mixing with, and depraving them: but where it is ufed without any view to painting over it, either in its own proper colour, or mixed with any other, particularly with black, it is preferable to hard enamel j beqaufe it can be worked with a much Jefs heat ; and confequently is both more ealy to be managed, and lefs liable to give occafion tp the warping or calcining the metal plates, or other bodies, on which it laid.
Ompofitim
28 x
Compo/ltim of enamel, of moderate bardnefs, but ■ more ferjeftbj
' N°3. ’
“ Take of flint glafs one pound, of calx of ** tin or putty of tne firft degree of whitenefs “ half a pound, of pearl afhes and common fait “ each four ounces, and of borax one ounce. “ Treat them as the foregoing: but the fire “ may be mure freely ufed than m the cafe of “ the la&”
This enapial* if the calx of tin or putty be perfe&lygood, will be very white; and is proper for dial-pjat(?s» or other fuch ufes ; where the purity of the white ground is eflential to the value of the work : and it will, alfo, bear colours very well, where ftch a ground is wanted for any painting; but if it be found too foft, in proportion to the fluxes of the colours, it may be prepared of a greater degree of hard* nefs by omitting the borax.
Cmpojition of foft enamel more perfectly white.
N 9 4.
“ Take of flint glafs one pound, of pearl (( afhes and common fait each four ounces, of “ borax two ounces, and of arfenic one ounce. “ Treat them according to the general direfti- « ons; but be fparing of the fire as with N° 2.” ^
This is too foft for a ground for colours: but is fit for any other purpofes where enamel of greater whitenefs is required; as alfo for ufing with other colours where there is occafion to paint with white.
Compofition of a very foft , of the frjl
. degree of whitenefs, proper for painting. .
' N° 5.
u Take of flint glafs one pound, of anti“ mony calcined to perfedt whitenefs accord- “ ing to the diredtions in p. 251, or of tin “ calcined with nitre according to the direc- “ tions in p. 250, half a pound, of pearl allies • “ and common lalt each three ounces, of bo- {f rax three ounces, and of arfenic one ounce. “ Proceed According to the general diredti- ** ons : but be very careful to avoid fuch a “ fufion, as will render the matter perfedtly ,c liquid.” •
This compofition produces an enamel extremely white, and very foft; and is proper to ufe, in painting, for linnen, or other objedts, where ftrong touches of white are advantageous. If it be found too foft, according to the tone of the fluxes, for the other colours, the arfenic may be omitted, and part of the borax; but it will, in this» proportion, fuit the other colours, when the fluxes arejudicioufly adapted to each kind.
Of common white glafs as an enamel ground.
The white glafs made at Mr. Bowie’s glafs- houfe in Southwork, is frequently ufed for the grounds of enamel dial-plates, and other painted works. It is a glafs rendered of an opake whitenefs by the admixture of a large proportion of arfenic, which, intimately mixed with the glafs by a flight fufion not fuffici- ent to produce a vitrific incorporation, retains its opacity; and, confequently, gives a whitened to the glafs; though if the fufion were long enough continued, it would aflimilate with the glals, and the whole mafs confe- qüèntly become perfectly tranlparent. This tendency to lofe its opacity, of courfe renders the uie of it, as a ground enamel, more limited and difficult: becaufe where colours are to be ufed, which require repeated burning, or to be continued a longer time in the fire, there will.be a great hazard of changing the opake whitenefs into tranfparency, or fuch an approach to it as deftroys the effedt of the ground: and, indeed, in the burning it, even as a ground, particular care is required in the manner. It is, like wife, harder than the Venetian common glafs, or any of the above pre- . parations of ground enamel: as likewife much more brittle, and liable to crack and peel off from the body painted with it: but notwith- Handing thefe difadvantages, its low price, and great whitenefs, which much furpaffes that of
the Venetian, or any enamel commonly to be had, have recommended it to the practice of • many, who are concerned in cheaper works of enamel.