POLISHING
AFTER an enameled piece has been stoned and fired for the last time, it
is often desirable to give the enamel a gloss or polish additional to
that which it naturally receives from the firing.
[Illustration:
FIG. 7. CARBORUNDUM OR EMERY STONE.
]
If the metal used is other than fine gold or fine silver it will be
black or oxidized when taken from the furnace, in which case it should
be “pickled,” that is, submerged for a minute or two, until the
oxidization is removed and the metal becomes bright, in a mild “pickle”
consisting of a warm solution of one part sulphuric acid and one part
water. The piece should now be rinsed in clean water, after which it
will be ready to be polished.
Polishing is best done on a lathe with a swiftly revolving wheel, say
about 2200 revolutions per minute. A wheel of from three to six inches
in diameter, made of hard felt or wood, is very satisfactory. If the
felt is thin it is often necessary to make a wooden back for it in order
to keep it flat.
The piece to be polished should be held on a small piece of leather or
felt so that the hands may not come in contact with the wheel, in which
case the skin and nails would soon be worn away. Rubber finger cots will
serve as an additional protection.
The enamel surface to be polished should first be covered with wet
pumice of about the consistency of mud. Then the pumice-covered surface
should be pressed against the face of the felt or wood wheel, and as
soon as the pumice is removed by the action of the wheel more wet
pumice-mud should be added so that the enamel surface may constantly be
kept covered with wet pumice.
It is best to use the finest ground pumice obtainable, although on rough
jobs a coarse grade may be used. Tutty powder (oxide of zinc) is said to
give even a better polish than fine pumice, and is often used after a
preliminary polish has been given by pumice. A different wheel should be
used for each polishing compound.
The polishing should be kept up until the enamel surface takes on the
desired gloss. This polishing process will cut away the metal quicker
than it does the enamel, so that any slight lines and scratches which
the metal received in the stoning will be removed by the polishing. Care
must be taken not to polish away too much of the metal, or to cut down
and destroy any metal ornaments which may be near the enameled part of
the piece. Felt wheels being more pliable than wood wheels have a
tendency to cut down the metal faster than they cut down the enamel (the
enamel being harder than the metal), while wood wheels tend to cut down
both parts equally. Felt wheels, however, are considered to give a
better and quicker polish.
When the piece is polished sufficiently, it should be rinsed and brushed
off in clean water, which will remove all trace of the pumice. The piece
is now finished as far as the enameling process is concerned, but may,
however, be plated, set with stones, engraved, etc., as may be desired.
If after the piece is polished it is found that there are a number of
small pit-holes in it, in which the pumice sticks even after the
brushing, this may be remedied by digging the pumice out with a scraper
or any sharp instrument. If the hole is small and the enamel transparent
it will scarcely show when clean owing to the refractive power of the
enamel. If, however, the hole is so large and noticeable as to be
objectionable it will have to be re-charged and re-fired. In such a case
it is often possible after the first firing to stone it smooth with a
Scotch stone or by polishing and thus avoid another firing.
------------------------------------------------------------------------