Page:Cyclopaedia, Chambers - Supplement, Volume 2.djvu/271

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named and confounded with other genera ; Ray has called it fedum a .but: Jiore. It properly belongs to the plants of the {hrub-kjnd, with dry fruits, and ought to be placed after the chamaerhododendros, in the regular arrangements of plants. Befide the common kind of this there is an African one, the leaves of which are fhorter and rounder than thofe of this fpecies, and which may be called the fhon-leaved African

POLiOPUS, in zoology, a name given by Aldrovand, and forne other authors, to the grmeita ; a fmall bird of the moor- hen kind. See Giunetta.

POLISHING (Cycl.)— Polishing of JheUs. This is an art of no long {landing in the world, in its prefent perfection ; and as the love of fea-fhells is become fo common among us, it may not be difagreeable to the reader to find Come inftruc- tions in executing fo pleafing a method of adding to their naiura! beauty, and the rules for which are at prefent fo little known, tho' the effect, of them be fo much efteemed. Among the immenfe variety of (hells, which we are acquaint- ed with, fome are taken up out of the fea, or found on its {bores in all their perfection and beauty ; their colours being all fpread by nature upon the furface, and their natural f-olijh fiiperior to any thing tlsat art could give. Where nature is jn herfelf thus perfc£t, it were madnefs to attempt to add any thing to her charms ; but in others, where the beauties are latent, and covered with a coarfer outer fkin, art is to be call- ed in, and the outer veil being taken off, all the internal beauties appear.

Among the {hells which are found naturally pdijhcd, are the porcelanes, the cafi'anders, thedolia, or concha: globofa?, the buccinums, the cornets, and the cylinders, or as they are generally, tho' improperly called, the rhombi ; excepting only- two or three, as the tiara, the plume, and thebuttertub-rbom- bus ; where there is an unpromifmg film on the furface, hiding a very great fhare of beauty within. Tho' the generality of the (hells of thefe genera are taken out of the fea in all their beauty, and in their utmoft natural po!iJ)j, there are feveral other genera in which all, or mod of the fpecies are tak"n up naturally rough and foul, and co- vered with an epidermis, or coarfe outer fkin, which is in many rough and downy, or hairy. 7'hetellinae, the mufcles, the cochlea?, and many others are of this kind. The more nice collectors, as naturalifls, infift upon having all their ihells in their native and genuine appearance, as they are found when living at fea ; but the ladies who make collections, hate the difagreeable outfuies, and will have all fuch polijhed : it wduld be very advifeable, however, for both kinds of col- lectors to have the fame {hells in different fpecimens, both rough and polijhed j the naturalift would by this means, be- iide knowing the outfide of the {hell, be better acquainted with its internal characters than he otherwife could be, and the lady would have a pleafure in comparing the beauties of the fhell in its wrought flate, to its coarfe appearance as na- ture gives it. How many elegancies in this part of the crea- tion muft be wholly loft to us, if it were not for the affift- ance of an art of this kind ! many {hells in their native ftate are like rough diamonds, and we can form no jufr. idea of their beauties till they have been poUfoed and wrought into form.

Tho' the art of polijlnng {hel!s is a very valuable one, yet it is very dangerous to the {hells ; for without the ut- moft care the means ufed to polijh and beautify a fhell will often wholly deftroy it. When a fhell is to be polijhed., the firft thing to be examined is, whether it have naturally a fmooth furface, or be covered with tubercles or promi- nences.

A fhell which has a fmooth furface and a natural dull piUJh, need only be rubbed with the hand, or with a piece of cha- moy leather, with fome tripoli or fine rottenftone v and it will be- come of a perfectly bright and fine pslijh. Emery is not to be ufed on this occafion, becaufe it wears away too much of the ftiell. This operation requires the hand of an experienced perfon, that knows how fuperficial the work muft be, and where he is to flop ; for in many of thefe {hells the lines are only on the furface, and the wearing away ever fo little of the fhell defaces them. A fhell that is rough, foul, and cruf- ty, or covered with a tartarous coat, muft be left a whole day fteeping in hot water : when it has imbibed a large quan- tity of this, it is to be rubbed with rough emery on a flick, or with the blade of a knife, in order to get oft" the coat. After this, it may be dipped in diluted aqua fortis, fpirit of fait, or any other acid ; and after remaining a few,momcnts in it, be again plunged into comm. n water. ■ This will great- ly add to the fpecd of the work. After this it is to be well rubbed with linnen cloths, impregnated with common foap ; and when by thefe feveral means it is made perfectly clean, the polijlnng is to be finiflicd with fine emery and a hair brufh. If after this the fhell when dry appears not to have fo <*ood upol'jl) as was defired, it muft be rubbed over with a folution of gum arabic; and this will add greatly to its dofo, without doing it any .fort of injury. The gum-water muft not be too thick, and then it gives no ftnfible coat, only heightening the colours. The white of an egg anfwers this purpofe al- fo very well ; but it is fubjedt to turn yellow. If the {hell Suppi. Vol. II.

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has an epidermis, which will by no means admit tht-0M><§ of it, .tis to be dipped feveral times in diluted aqua fortis", that this may be eaten off; and then the fhell is to be fclijbed in the ufual way with putty, fine emery, or tripoli, on the hair of a fine brufh. When it is only a pellicle that hides the colours, the fhells muft be fteeped in hot water, and after that the fkin worked off by degrees with an old file. This is the cafe with feveral of the cylinders, which have not the natural 'polijh of the reft.

When a fhell is covered with a thick and fatty epidermis, as is the cafe with feveral of the mufcles and tellinse : in this cafe aqua fortis will do no fervice, as it will not touch the fkin i then a rough brufh and coarfe emery are to be ufed ; and if this does not fucceed, feal-fkin, or as the workmen call it fijh shn and pummkc-Jlone, are to be taken in to aflift. When a fhell has a thick cruft, which will not give way to any of thefe means, the only way left is to plunge it feveral times into ftrong aqua fortis, till the ftubborn cruft is wholly eroded. The limpets, auris marina, the helmet-fhells, and feveral other fpecies are of this kind, and muft have this fort of management ; but as the defign is to ftiew the hidden beau- ties under the cruft, and not to deftroy the natutal beautv and polijh of the infide of the fhell- the method of ufini the aqua fortis muft be this : A long piece of wax muft b% provided, and one end of it made perfectly to cover the whole mouth of the fhell; the other end will then ferve as a handle, and the mouth being flopped by the wax, the li- quor cannot get m to the infide to fpoil it; then there muft be placed on a table, a vefTcl full of aqua fortis, and another full of common water.

The fhell is to be plunged into the aqua fortis; and after re- maining a few minutes in it, is to be taken out and plunged into the common water. The progrefs the aqua fortis makes in eroding the furface is thus to be carefully obferved every time it is taken out: the point of the fhell, and any other

1 wax, to prevent the aqua

tender parts, are to he covered with \

fortis from eating them away ; and if there be any worm- holes, they alfo muft be flopped up with wax, otherwife the aqua fortis would foon eat thro' in thofe places. When the repeated dippings into the aqua fortis fliew that the coat is fufficiently eaten away, then the fhell is to be wrought care- fully with fine emery and a brum ; and when it is polijhed as high as can be by this means, it muft be wiped clean and rubbed over with gum-water, or the white of an egg. In this fort of work the operator muft always have the "caution to wear gloves, otherwife the Ieaft touch of the aquafortis will burn the fingers, and turn them yellow ; and often if it be not regarded, will eat off the fkin and the nails. Thefe are the methods to be ufed with fhells, which require but a moderate quantity of the furface to be taken off; but there are others which require to have a larger quantity taken oft, and to be uncovered deeper ; this is called entirely foil- ing a fheil. This is done by means of an horizontal wheel of lead or tin, impregnated with rough emery; and the ftiell is wrought down in the fame manner in which rtones are wrought by the lapidary. Nothing is more difficult, how- ever, than the performing this work with nicety : very often fhells are cut down too far by it, and wholly fpoile : ; and to avoid this, a courfe vein muft be often left (landing in fome place, and taken down afterwards with the file, when the cut- ing it down at the wheel would have fpoiled the adjacent parts.

After the (hell is thus cut down to a proper degree, it is to be polijhed with fine emery, tripoli, or rotten ftone, with a wooden wheel turned by the fame machine as the leaden one, or by the common method of working with the hand with the fame ingredients, when a fhell is full of tubercles, or protuberances, which muft be preferved. It is then impof- fible to ufe the wheel ; and if the common way of dipping into aqua fortis be attempted, the tubercles being harder than the reft of the ftiell, will be eat thro' before the reft is fuf- ficiently fcaled, and the fhell will be fpoiled : in this cafe in- duflry and patience are the only means of effecting a ps.'ijb. A camel's hair pencil muft be dipped in aqua fortis, and with this the intermediate parts of the fhell muft be wetted, leav- ing the protuberances dry : this is to be often repeated, and after a few moments the fhell is always to be plunged into water to ftop the erolion of the acid, which would other- wife eat too deep, and deftroy the beauty of the fhell. When this has fufficiently taken off the foulnefs of the fhell, it is to be poiijlicd with emery of the fineft kind, or with tripoli ; by means of a ImalJ ftick, or the common polijhing ftone ufed by the goldfmiths maybe ufed.

1 his is a very tedious and troublefome thing, efpecially when the echinated oyfiers and murexes, and fonie other fuch fhells are to be wrought ; and what is worft of all is, that when all this pains has been taken, the bufinefs is not well done; for there ftill remain feveral places which could not be reached by any inftrument ; fo that the fhell muft necefl'arily be rubbed over with gum-water, or the white of an egg afterwards, in order to bring out the colours and give a glofs ; in fome cafes it is even neceffary to give a coat of varnifh. Thefe are the means ufed by zitifts to brighten the colours, and add to the beautv of ihells ; and the"cbaneeb produced 2 S f bv