CONCHOLOGY, ' 37 
if this does not fucceed, feal-(fcin, or fifli-fkin, and pu- 
mice-ftone, are to be employed; When a fliell has a thick 
cruft, which will not give way to any of thefe means, the 
only mode left is to plunge it feveral times into ftrong 
aquafortis, till the ftubborn cruft is wholly eroded. The 
limpets, aures marinre, helmet-fhells, and feveral other 
fpecies of this kind, muft have this fort of management; 
but as the delign is to (how the hidden beauties under 
the cruft, and not to deftroy the natural beauty and po- 
lifli of the infide of the fliell, the aquafortis fliouid be uled 
in the following manner: A long piece of wax muft be 
provided, and one end of it made perfeftly to cover the 
■whole mouth of the (hell; the other end ferves as a han¬ 
dle, and the mouth being flopped by the wax, the liquor 
cannot get in to the infide to fpoil it; then there muft be 
placed on a table a veil'd full of aquafortis, and another 
full of common water. The fliell is to be plunged into 
the aquafortis, and after remaining a few minutes in it, 
is to be taken out, and plunged into the common water. 
The progrefs the aquafortis makes in eroding the furface 
is thus to be carefully obferved every time it is taken 
out: the point of the fliell, and any other tender parts, 
are to be covered with wax, to prevent the aquafortis 
from eating them away; and if there be any worm-holes, 
they alfo muft be flopped up with wax, otherwife the aqua¬ 
fortis will quickly eat through in thofe places. When 
the repeated dippings into the aquafortis fhow that the 
coat is fufficiently eaten away, then the fhell is to be 
wrought carefully with fine emery and a brulh; and when 
it is polilhed as high as it will bear, it muft be wiped 
clean, and rubbed over with gum-water, or the white of 
an egg. In this fort of work the operator fliouid wear 
gloves, otherwife the leaft touch of the aquafortis will 
burn the fingers, and often, if not regarded, eat away 
the fkin and the nails. 
Thefe are the methods to be taken with fliells which 
require only a moderate quantity of the furface to be 
eaten off; but there are others which require to have a 
larger quantity taken off, and to be uncovered deeper: 
this is called entirely fcaling a fliell. This is done by means 
of a horizontal wheel of lead or tin, impregnated with 
rough emery; and the fliell is worked down in the fame 
manner in which Hones are wrought by the lapidary: 
both figures of the nautilus-fhell given in the Conchology- 
Plate III. were worked down in this manner. Nothing 
is more difficult, however, than the performing this work 
with nicety; very often ffiells are cut dowm too far by it, 
and wholly fpoiled : and to avoid this, a coarfe vein muff 
be often left Handing in fome place, and taken down af¬ 
terwards with the file, when the cutting it down at the 
wheel would have .defaced the adjacent parts. 
After the fliell is thus cut down to a proper degree, it 
is to be polifhed 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 fliell is full 
of tubercles, or protuberances, w'hich are to be prefevved, 
it is then impoflible to ufe the wheel ; and if the common 
way of dipping into aquafortis be attempted, the tuber¬ 
cles being harder than the reft of the fliell, will be eaten 
through before the reft is fufticiently fcaled, and the fhell 
will be fpoiled. In this cafe, induftry and patience are 
the only means of effedling a polifh. A camel’s-hair pen¬ 
cil muft be dipped in aquafortis, and with this the inter¬ 
mediate parts of the fliell muft be wetted, leaving the pro¬ 
tuberances dry ; this is to be often repeated, and after a 
few moments the fliell is always to be plunged into wa¬ 
ter, to flop the too great erofion of the acid, which would 
otherwife penetrate too deep, and deftroy the beauty of 
the fliell. When this lias fufficiently taken off the foul- 
nefs of the fliell, it. is to be polifhed with emery of the 
fineft kind, or with tripoli, by means of a fmall flick, or 
the common polifhing-ftone uled by the goldfmiths. This 
is a very tedious and troublefome operation, efpecially 
when the echinated oyfter .3 and murices, and other fimihir 
Vol. V. No. 252, 
fhells are to be wrought; and what is won't of all, is, that 
when this labour has been employed, the bufinefs is not. 
fufficiently done; for there Hill remain feveral places which 
could not be reached by any inftrument, lb that the fliell 
muft be rubbed over with gum water or the white of an 
egg, in order to bring out the colours, and give a glofs ; 
in fome cafes it is even neceffary to add a coat of varnifli. 
Thefe are the means ufed by artifts to brighten the co¬ 
lours and add to the beauty of fhells ; and the changes 
produced by polifliing in this manner are fo great, that 
the fliell-can fcarcely be known afterwards to be the fame; 
and hence we fometimes hear of new fhells in the cabinets 
of collectors, which have no real exiftence as feparate 
fpecies, but are fhells difguifed by polifliing, and are thus 
fraudulently impofed upon the hafty and unwary coilec 
tor. To caution the young concholcgiil againft errors 
of this kind, it may be proper to mention the molt re¬ 
markable fpecies thus ufually altered. The onyx-fiiell or 
volute, called the purple or •violet-tip, which in its natural 
Hate is of a Ample pale brown, when it is wrought (lightly, 
or polifhed with only the fuperficies taken off, is of a fine 
bright yellow ; but when it is eaten away deeper, it ap¬ 
pears of a fine milk white, with the lower part bluifh: it 
is in this (late called the onyx-/hell ; and it is preferved in 
many cabinets in its rough (late, and in its yellow appear¬ 
ance, as different fpecies of fhells. 
The violet (hells, fo common among the curious, is a 
fpecies of porcelain, or common cowry, which does not 
appear in that elegance till it has been poliflied ; and the 
common auris marina (hows itfelf in two or three diffe¬ 
rent forms, as it is more or lefs deeply wrought. In its 
rough Hate it is dufky and coarfe, of a pale brown on tiio 
outfide, and pearly within ; w hen it is eaten down a little 
way below the furface, it (hows variations of black and 
green; and when (till farther eroded, it appears of a fine 
pearly hue within and without. The nautilus, when it is 
poliflied down, appears all over of a fine pearly colour; 
but when it is eaten away but to a fmall deptii, it appears 
of a fine yellowifli colour with dufky hairs. The burgau, 
when entirely cleared of its coat, is of the mod beautiful 
pearl-colour; but when (lightly eroded, it appears of a 
variegated mixture.of green and red,whence it has been 
called the parroquet. The common helmet-fliell, when 
Wrought, is of the colour of the fineft agate; and the 
mufcles, in general, though very plain fhells in their com¬ 
mon appearance, become beautiful when poliflied, and 
fhow large veins of the molt elegant colours. The Perfian 
fliell, in its natural ftate, is all over white, and covered 
with tubercles; but when it has been ground down on a 
wheel, and polifned, it appears of a grey colour, -with 
fpots and veins of a bright and highly polilhed white. 
The limpets, in general, become very different when po¬ 
liflied, mod of them (hewing bright and elegant colours; 
among thefe the tortoife-flieil limpet is the principal; it 
does not appear at all of that colour or tranfparence till it 
lias been wrought. 
That elegant fpecies of fhell called the jonquil-cbama, 
which lias deceived fo many into an opinion of its being 
a new fpecies, is only a white chama with a reticulated 
furface ; but when this is poliflied, it loles at once its retie 
cular work and its colour, and becomes perfectly finooth, 
and of a fine bright yellow. The violet-coloured chama 
of New England, when worked down and polifhed, is of 
a fine milk white, with a great number of blue veins, dif- 
pofed like the variegations in agates. The affes-ear fhell, 
when poliflied after working it down with the file, be¬ 
comes extremely gloffy, and obtains a fine roie-colour all 
about the mouth. Thefe are fome of the mod frequent 
among an endlefs variety of changes wrought on (hells 
by polifliing; and we find there are many of the very 
greateft beauties of this part of the creation which mult 
have been loft but for this method of fearching deep into 
the fubftance of the fliell for them. 
The Dutch are very fond of (hells, and are very nice 
in their manner of working them ; they are under no re- 
i. ftraint; 
