COP

COP

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As it is a procefs of fome nicety to producea true folution of copal fit for the purpofe of avarnifh without impairing the colour, fome ofthe directions laid down by practical artifts mayJiere be inferted. The following is given byMr. Sheldrake 1 as the refult of long practicalpbfervation. Reduce two ounces of copal tocoarfe powder (not fine) put it into a glafs velfeland pour thereon a mixture of one pint of thebelt oil of turpentine with one-eighth of fpiritof fal ammoniac, previoufly well fhaken, corkthe glafs, leaving a fmall hole through the cork,to allow the efcape of the fpirituous vapour,.and fpeedily heat it to that point at which thebubbles may be counted as they rife to the fur-face. Continue this heat, neither increafingnor leffening it, till the folution is compleat, ortill no more will diflolve. The mixture becomesfomewhat milky at firft, then the upper furfaceclears, whilft the copal fwells, foftens, becomesopake, and gradually diffufes itfelf through thefpirit, diffolving therein. It fhould feem thatthis procefs requires much nicety of manage-ment in regulating the heat, for if ever this isincreafed tbe bits of copal refume their tranfpa-rency, b no longer coalefce, and remain after-wards perfectly infoluble. It is alfo of theutmoft confequence that the oil of turpentinebe of the beft fort, and very highly rectified.The veffel fhould not be opened till quite cold,otherwife the fudden efcape of the vapour willcarry out with it a great part of the folution.This varnifh is of a rich deep colour whenviewed in the bottle, but gives no fenfible colourwhen laid on.

Copal may alfo be united with oil of tur-pentine very conveniently by the intermede of■other elfential oils, particularly oil of fpike, oroil of lavender. The following procefs is givenby M. Tingry. c Put 2 ounces of elfential oilof lavender into a glafs matrafs heated by alamp, or over a moderate fire, add thereto whenvery warm one ounce of copal grofsly pow-dered, and at different times flirring it with aflick of white wood; when the copal is diffolvedadd 6 ounces of boiling oil of turpentine, di-viding it into three dofes at as many differenttimes, and keep flirring till the whole is uni-formly mixed. This varnifh will be of a finegold colour, very durable and brilliant.

Ether is alfo a good folvent for copal. d Re-duce half an ounce of copal to fine powder, andput it by fmall portions into a flafk containing2 ounces of cold fulphuric ether of the pureft

• Tranfaft, of the Society of Arts . 1 Phil. Jour. vol. 9* Tingry. • Sheldrake.

kind. Shake it well, and in fome hours the fo-lution will be complete. If the liquor is notperfectly clear add more ether.

The remarkable effe£t of camphor .in pro-moting the folution of the refins has been men-tioned under that article. With none is thisproperty fhewn more ftrikingly than with copal.When the two are feparately powdered andthen mixed, the copal abforbs the camphor,fwells, and foftens into one coherent mafs whichwill remain for fix months of the fame pallyconfiftence, though kept in a warm dry room.'By the intermede of camphor, copal may becompletely diffolved in alcohol. Diffolve half anounce of camphor in a pint of alcohol, put itinto a glafs veffel over a moderate fire, and addfour ounces of copal in fmall pieces, continuethe heat that the bubbles may be counted, tillthe folution is complete. A part of the copalwill feparate when the liquor is cold, butenough will be retained to give a fine colour-lefs varnifh.

Camphor alfo aflifls the folution of copal inoil of turpentine according to the following pro-cefs, alfo given by Mr. Sheldrake. Diffolve halfan ounce of camphor in a quart of oil of tur-pentine, take a piece of copal the fize of a wal-nut, bruize it into coarfe powder, add it to thecamphorated oil of turpentine, and bring it toboil as foon as poflible , then keep it gently boilingfor an hour, and enough of the copal will bediffolved to form a good varnifh. The veffel(glafs or tin) in which the folution is madefhould be clofely corked, leaving only a veryfmall hole for the efcape of the vapour to pre-vent the veffel from burfting, an accident which(from the extreme combuftibility of the ingre-dients) might be attended with very feriousconfequences.

The above procefs fhould be followed pre-cifely, for if the camphor is not added firft, orif the copal is in fine powder, thefe two fub-ftances at once unite, forming a mafs like bird-lime at the bottom of the veffel, and the folu-tion will not go on.

Copal may alfo be diffolved according toDemmenie/ by being fufpended in a glafs re-ceiver over alcohol or oil of turpentine, andapplying heat to make the liquor boil. Thevapours arifing from it liquify the copal whichfalls in drops into the boiling fluid, and immedi-atley diffolves.

For a copal varnifh which is to unite thequalities of tranfparency and durability, to a

, 8vo. * The Painter’s and Varniflicr’s Guide, 1804.

' Fhil. Jour, vol, a. p. 14a.