SECTION III.
Of particular oils.
Of linfeed oil.
LINSEED oil is exprefled from the leed of line, by thofe who manufacture it in large quantities, and have mills turned by water for the more expeditious dilpatch of the work : it is the principal oil ufed in all kinds of paint-ings ; or, indeed, the only kind, except for feme very nice purpofes, where its brownnefs renders it unfit. The general defects of lin-feed oil are this brown colour, and a tardinefs in drying ; both which are in a much greater degree in fome parcels than others; and there is fometimes formed fuch, as,.inconfequence of its being commixed with the oil of fome other vegetable (accidentally growing with it) that partakes of the nature of olive oil, can-not be brought to dry by any art or means whatever.
The goodnefs of linfeed oil, therefore, con-fifts in its nearer approach to a colourlefs ftate; jfod in its drying foon. Its ftate, with refpeCt
to the firft quality, may of courfe be diftinguifh- ed by infpedtion only: but the latter can only be difcovered by adtual trial of it j for there is jio particular appearance, or other perceptible mark, attending this quality.
JLin&ed oil is in general ufed without any other preparation than the mixing it with the proper-dryer : but the keeping it a confider- «ble time before it be ufed, will always be ibtfnd to improve it. It is, neverthelefs, ufed Sometimes, after it is prepared into the ftate of drying oil, not to commix and make other unprepared parcels dry, but alone, as the fble vehicle of the colours. The convenience of this is the fpeedy drying of the paint fo com- pofed j but it cannot be praftifed where the beauty of the colour is of the leaf! confequence; for the oil imparts in this cafe a very ftrong brown to the mixture.
' • ; Of nut oil.
• Nut oil is the oil of walnuts prefTed out of :the kernels by 'means of a fcrew-prefs. It is ufed for the mixing with flake white, or other .pigments, where the clearnefs of the colour is of great confequence, and would be injured by the brownnefs of linfeed oil.
It is ufed without any other preparation than keeping, which is always of advantage •to it», both with regard to its colour and quality of drying.
The faults of nut oil, When not good, Hi the being turbid, and not perfectly colourlcf* ) and the drying too flowly : the firft fhewfc it* felf ; but the other mult be examined by trial. If, however, there be hd adulteration in die cafe, time will generally cürè it of all thefe defects.
Whoever would have nut oil perfectly good, fhould peel off the fkin of the kernels befbtt they be preflèd, in the fame manner a& wheA they are eaten : for the fkihs contain an acrid oil of a very diffèrent nature from that of die white fubftance of the kernel j whichis extremely fubjeCt to turn brown, dr Oven black and confèquently tinge the other when Mttfc mixt with it.
Of poppy oil.
Poppy oil is exprefled from the ripe feeds o£r poppies, in the fame manner as nut oil fronte the walnuts. Its qualities and ufes, as like— wife its defects and the remedy for them, ar^ alfo much the fame as thofe of the nut oil f only when it is perfectly good, it is mörè deaf and limpid, and will dry better than the béfft nut oil whatever.
Oil of fpike and lavender.
Oil of fpike or lavender are efleritial oi diftilled oils, obtained by diftilling thé fpilce or any other lavender, with water. It is ufed in painting only as the vehicle for laying Oft the compofition formed of the flax and colours in enamel painting; which by its fluidity k renders capable of being worked with a pencil; its volatile nature afterwards making it Wholly dry away without leaving any matter that might affe£t the fubftances of the enamel; which would be otherwife, if any but an e£- fential oil were ufed.
Oil of fpike or lavender is fubje£t to be adulterated by the oil of rofemary; which, though much of the fame nature, yet being of a lefs undtuous or thick confluence, is not £> well adapted to make the colours fpread and work well with the pencil. This adulteration is not eafily difcoverable, where it cannot be diftinguilhed by the fmell; and the belt method therefore to be certain of the goodncfe of the oil of fpike or lavender for tins purpofe, is to make an adtual trial of it.