ENAMELLING. 
by rubbing the work with rotten-stone 
upon a small straight bar of pewter. Some 
delicacy is here required to avoid scratching 
nr producing flaws in the enamel by press- 
ing too hard. In this way the piece is ren- 
dered perfectly even. But the last bril- 
liant polish is given by a piece of deal wood 
and the same rotten-stone. 
This is the general method of applying 
enamel; but some colours require more 
precaution in the management of the fire. 
Opaque colours require less management 
than the transparent. A variety of cir- 
cumstances must be attended to in transpa- 
rent colours ; every colour requires gold of 
a particular fineness. 
When different colours are intended to 
be placed beside one another, they are kept 
separate by a small edge or prominency, 
which is left in the gold for that purpose, 
and is polished along with the enamel. 
The enamelling upon silver is effected 
nearly in the same manner as that of gold ; 
but the changes sustained by the colours 
upon silver by the action of the fire are 
much more considerable than when gold 
is used. 
Copper is not much used by enamellers, 
on account of the difficulty which attends 
the attempt to fix beautiful colours upon it. 
When this metal is used, the common 
practice is to apply a coating of opaque 
white enamel, and upon this other colours 
which are more fusible than the white. 
A good effect is produced in toys by 
leaving part of the gold bare. For this 
purpose its surface is cut into suitable com- 
partments by the engraver. This, Ifowever, 
is an expensive method, and is for this rea- 
son occasionally imitated by applying small 
and very thin pieces of gold upon the sur- 
face of the enamel, where they are fixed by 
the fire, and afterwards covered by a trans- 
parent vitreous coating. 
A method of taking off the enamel from 
any toy without injuring the metallic part, 
is often a desirable object.- For this pur- 
pose a mixture of common salt, nitre, and 
alum in powder, is applied upon the ena- 
mel, and the piece is put into the furnace. 
As soon as the fusion ha6 taken place, the 
piece is to be suddenly thrown into water, 
which causes the enamel to fly off, either 
totally or in part. Any part which may 
still remain is to be removed by repeating 
the same operation a second time. 
To coat vessels of iron or copper for cu- 
linary purposes with an enamel capable of 
defending the metal from the action of any 
solvent, and for enduring any heat or 
transition from heat to cold, appears a de- 
sirable object ; and many experiments 
' have been made on the subject by Mr. 
Soen Rinman of the Royal Academy of 
Stockholm. 
The following compositions he found 
answer very well on copper. 1. ”1 he white 
semitransparent fluor spar and sulphate of 
lime in equal quantities, powdered, mixed, 
and calcinated in a white heat ; then pow- 
dered, made into a thin paste with water, 
and applied a little warm to the vessel also 
warmed. Then dried and heated gradually to 
a certain point, a very strong heat, greater 
than is generally obtained in an assaying fur- 
nace, is to be applied as quickly as possible. 
2. Sixty parts of lime, one hundred of 
fluor spar, sixty of gypsum, twenty of 
quartz, and one of manganese are calci- 
nated, ground, and applied in a similar 
manner. 3. Four parts of fluor spar, four 
of gypsum, and one of litharge, melted 
into a straw-coloured glass, ground and ap- 
plied in the same way, required a much 
stronger heat. 4. Five parts of fluor spar, 
five of gypsum, two of minium, two of flint 
glass, half a part of borax, the same of oxide 
of tin, and one twenty-fifth of a part of oxide 
of cobalt melted together made an enamel; 
which, when ground, and applied as the 
others, fused with a less degree of heat. 
This, Mr. Rinman imagines, would have 
been acted upon in length of time by sul- 
phuric acid. The oxide of cobalt was pre- 
pared by saturating a solution of cobalt in 
aqua-fortis with common salt, and evapo- 
rating to dryness. 
As these would not do for iron, he tried 
the following : 1. minium, nine parts ; 
flint glass, six ; pure potash, two ; nitre, two ; 
borax, one ; were ground together, put into 
a covered crucible, which they only half 
filled and fused into glass. This poured 
out on a piece of marble, quenched in wa- 
ter, powdered and made into a thin paste, 
was laid on both sides of an iron vessel. 
After having been dried and heated gra- 
dually, the vessel was put under a muffle, 
well heated in an assaying furnace, and in 
half a minute the enamel melted. The 
vessel being then withdrawn, was found 
enamelled of a beautiful black colour, which 
appeared to be owing to a thin layer of 
oxided iron seen through the transparent 
glaze. 2 The same, with one hundredth 
part of oxide of cobalt prepared as above, 
covered the vessel more perfectly with a 
blue enamel. 3. The same ground with 
