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28 SWEDENBORG’S TRAVELS AND DIARIES. [Doc.205.
which cannot be revolved in every direction, but which is
drawn lengthways up and down the glass ; the red English
earth dissolved in water being constantly applied to it. This
operation generally lasts twelve hours. Meanwhile the plate
of glass appears perfectly polished and smooth, and is reduced
.
to the required thickness, and ready for being converted into
a mirror. This last machine is arranged like the former with
the difference that the upper grinder is smaller.
With respect to the fastening of the foil to the glass,
that a mirror may be produced , this is done in the
following way: 1. Tables of marble or stone are provided of
the proper size, and of such a quality, that they can be
polished in the best style ; otherwise glass tables answer the
purpose; these tables are furnished with a rim all round.
2. Tin-foil is required, so thin, that one hundred foils placed
above one another are scarcely half an inch in thickness.
3. This tin-foil is spread on the table and quick-silver poured
upon it ; and these amalgamate. Upon this the plate of glass
is placed , and upon the glass, weights ; in the middle weights
of brick and on the sides weights of lead ; with these the plate
of glass is thoroughly loaded. 4. In this condition it is left
for a whole night. The tin and quick-silver are meanwhile
amalgamated ; the tin disappears, and they are both attached
to the glass and remain firmly united to it, and thus the plate
of glass is converted into a mirror. 5. The superfluous part
of mercury flows off of its own accord ; but in case any of
it still adhere, the mirrors are now raised obliquely, and
all the superfluous metal, which would still have remained,
flows off. 6. The foiling of cut glass shall now be described.
For lately a process has been discovered by which figures are
cut on the back of a plate of glass, so as to produce the
appearance of the engraving being on the front. In order
that the foil may enter into these excavations and folds, the
plate is put back again upon a layer made of cloth of Indian
wool, folded several times, and upon this some weights are
laid, so that the foil may enter more readily into the incisions
and excavations made upon the glass.
With respect to the attenuation of tin into foil the follow
ing particulars may be mentioned : 1. For this purpose only
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