Chap. Vi'. CONCH 
Of the Ha- butter-tub rhombus, where there is an unpromifmg 
«n! T n ti0 £° f on t ^ ie ^ ur ^ ace ) hiding a very great (hare of beau- 
ie s, c. within. Though the generality of the lhells of 
thefe genera are taken out of the fea in all their beau- 
ty, and in their utmoft natural polifli, there are feve- 
ral other genera, in which all or moll of the fpecies 
are taken up naturally rough and foul, and covered 
with an epidermis, or coarfe outer Ikin, which is in 
many rough and downy or hairy. The tellinse, the 
muffels, the cochleae, and many others, are of this 
kind. The more nice colleftors, as naturalills, infill 
upon having all their lhells in their native and genuine 
appearance, as they are found when living at fea ) but 
others who make colleftions, hate the difagreeable 
outfides, and will have all fuch polilhed. It would be 
very advifable, however, for both kinds of collectors to 
have the fame lhells in different fpecimens both rough 
and polilhed : the naturalill would by this means, be- 
fides knowing the outfide of the Ihell, be better ac- 
quainted with its internal charaflers than he otherwife 
could be ) while thofe who wilh to have them polilhed, 
might compare the beauties of the Ihell, in its wrought 
Hate, to its coarfe appearance as nature gives it. How 
many elegancies in this part of the creation mull be 
wholly loll to us, if it were not for the alfillance of an 
art of this kind ! Many lhells in their native Hate are 
like rough diamonds ; and we can form no juft idea of 
their beauties till they have been polilhed and wrought 
into form. 
Though the art of polilhing lhells is a very valuable 
one, yet it is very dangerous to the lhells ) for without 
the utmoft care, the means ufed to polifh and beautify 
a Ihell often wholly deftroy it. When a Ihell is to be 
polilhed, the firft thing to be examined, is whether it 
have naturally a fmooth furface, or be covered with tu- 
bercles and prominences. 
A Ihell which has a fmooth furface, and a natural 
dull polilh, need only be rubbed with the hand, or with 
a piece of chamoy leather, with fome tripcdi, or line 
rotten Hone, and it will become of a perfectly bright and 
fine polilh. Emery is not to be ufed on this occafion, 
becaufe it wears away too much of the ihell. This 
operation requires the hand of an experienced perfon, 
that knows how fuperficial the work mull be, and where 
he is to Hop 3 for in many of thefe lhells the lines are 
only on the furface, and the wearing away ever fo little 
of the Ihell defaces them. A Ihell that is rough, foul, 
and crufty, or covered with a tartareous coat, mult be 
left a whole day fteeping in hot water : when it has im- 
bibed a large quantity of this, it is to be rubbed with 
rough emery on a flick, or with the blade of a knife, 
in order to get off the coat. After this, it may be 
dipped in diluted aquafortis, fpirit of fait, or any other 
acid ; and after remaining a few moments in it, be again 
plunged into common water. This will add greatly to 
the Ipeed of the work. After this it is to be well 
rubbed with linen cloths, impregnated with common 
foap ) and when by thefe feveral means it is made per- 
fectly clean, the polilhing is to be finilhed with fine 
emery and a hair-brulh. If after this the Ihell when 
dry appears not to have fo good a polilh as was defired, 
it mull be rubbed over with a folution of gum arable 3 
and this will add greatly to its glofs, without doing it 
the fmalleft injury. The gum- water mull not be too 
thick, and then it gives no fenfible coat, only heighten- 
Voj.. YI. Part II. 
.M3 
With lea- 
ther. 
O L O G Y. 481 
ing the colours. The white of an egg anfwers this pur- Of the Ha- 
pole alfo very well 3 but it is fubjecl to turn yellow. 
If the Ihell has an epidermis, which will by no means \ 
admit the polilhing of it, it is to be dipped feveral times 
in diluted aquafortis, that this may be eaten off 3 and 
then the Ihell is to be polilhed in the ufual way with 
putty, fine emery, or tripoli, on the hair of a fine brulh. 
When it is only a pellicle that hides the colours, the 
Ihell mull be fteeped in hot water, aqd after that the 
Ikin worked off by degrees with an old file. This is 
the cafe with feveral of the cylinders, which have not 
the natural polilh of the reft. 
When a Ihell is covered with a thick and fatty epi- 
dermis, as is the cafe with feveral of the muffels and 
tellinse 3 in this cafe aquafortis will do no fervice, as it 
will not touch the Ikin : then a rough brulh and coarfe 
emery are to be ufed 3 and if this does not lucceed, ^ 
feal-lkin, or, as the workmen call it, JiJh-Jkin and pit- m ic C .ftone. 
mice-Jlone , are t© be employed. 
When a Ihell has a thick cruft, which will not give 
way to any of thefe means, the only way left is to 
plunge it ieveral times into ftrong aquafortis, till the 
ftubborn cruft is wholly eroded. The limpets, auris 
marina, the helmet-lhells, and feveral other fpecies of 
this kind, mult have this fort of management 3 but as 
the delign is to Ihow the hidden beauties under the 
cruft, and not to deftroy the natural beauty and polilh 
of the inlide of the Ihell, the aquafortis mull be uied in 
this manner : A long piece of wax mult be provided, 
and one end of it made perfectly to cover the whole 
mouth of the Ihell 3 the other end will then ferve as a 
handle, and the mouth being Hopped by the wax, the 
liquor cannot get into the inlide to fpoil it 3 then there 
mull be placed on a table a veffel full of aquafortis, and 
another full of common water. 
The Ihell is to be plunged into the aquafortis) and With acids, 
after remaining a few minutes in it, is to be taken & c * 
out, and plunged into the common water. The pro- 
grefs the aquafortis makes in eroding the furface is 
thus to be carefully obferved every time it is taken 
out : the point of the Ihell, and any other tender parts, 
are to be covered with wax, to prevent the aquaiortis 
from eating them away ) and if there be any worm- 
holes, they alfo mult be Hopped up with wax, other- 
wife the aquafortis would loon eat through in thofe 
places. When the repeated dippings into the aqua- 
fortis Ihow that the coat is fufficiently eaten away, 
then the ihell is to be wrought carefully with fine 
emery and a brulh ) and when it is polilhed as high as 
can be by this means, it mull be wiped clean, and 
rubbed over with gum-water or the white of an egg. 
In this fort of work the operator mull always have the 
caution to wear gloves ) otherwife the icall touch of 
the aquafortis will burn the fingers, and turn them yel- 
low 3 and often, if it be not regarded, will eat off the 
Ikin and the nails. 
Thefe are the methods to be ufed with lhells which 
require but a moderate quantity of the furface to be 
taken off 3 but there are others which require to have a 
larger quantity removed, and to be uncovered deeper ; 
this is called entirely foaling a fhell. This is done by 
means of a horizontal wheel of lead or tin, impreg- 
nated with rough emery ) and the Ihell is wrought down 
in the fame manner in which ftones are wrought by the 
lapidary. Nothing is more difficult, however, than the 
3 P performing 
