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Page 17
A fine black varnish suitable for the covering of broken places in
sewing machines and similar articles, where the japanned surface has
become injured or scratched, can be made by taking some fine
lamp-black or ivory-black, and thoroughly mixing it with copal
varnish. The black must be in a very fine powder, and to mix the more
readily it should be made into a pasty mass with turpentine. For the
ordinary repairing shop this will be found very handy.
The following is a simple way for tarring sheet-iron pipes to prevent
rusting. The sections as made should be coated with coal tar, and then
filled with light wood shavings, and the latter set alight. The effect
of this treatment will be to render the iron practically proof against
rust for an indefinite period, rendering future painting unnecessary.
It is important, of course, that the iron should not be made too hot,
or kept hot for too long a time, lest the tar should be burnt off.
The following is a varnish for iron and steel given by a recognized
authority: 5 parts of camphor and elemi, 15 parts of sandarach, and
10 parts of clear grains of mastic, are dissolved in the requisite
quantity of alcohol, and applied cold.
Another good black enamel for small articles can be made by mixing 1
lb. of asphaltum with 1 lb. of resin in 4 lb. of tar oil, well heating
the whole in an iron vessel before applying.
A good brown japan can be prepared by separately heating equal
quantities of amber and asphaltum, and adding to each one-half the
quantity by weight of boiled linseed oil. Both compounds are then
mixed together. Copal resin may be substituted for the amber, but it
is not so durable. Oil varnish made from amber is highly elastic. If
it is used to protect tin-plate printing, when the plates after
stoving have been subsequently rolled so as to distort the letters,
the varnish has in no way suffered, and its surface remains unbroken.
A bronzing composition for coating iron consists of 120 parts mercury,
10 parts tin, 20 parts green vitriol, 120 parts water, and 15 parts
hydrochloric acid of 1.2 specific gravity.
SECTION VI.
PROCESSES FOR TIN-PLATING.
In these days of making everything look what it is not, perhaps the
best and cheapest substitute for silver as a white coating for table
ware, culinary vessels, and the many articles requiring such a
coating, is pure tin. It does not compare favourably with silver in
point of hardness or wearing qualities, but it costs very much less
than silver, is readily applied, and can be easily kept clean and
bright. In tinning hollow ware on the inside the metal article is
first thoroughly cleansed by pickling it in dilute muriatic or
sulphuric acid and then scouring it with fine sand. It is then heated
over a fire to about the melting-point of tin, sprinkled with powdered
resin, and partly filled with melted pure grain tin covered with resin
to prevent its oxidation. The vessel is then quickly turned and rolled
about in every direction, so as to bring every part of the surface to
be covered in contact with the molten metal. The greater part of the
tin is then thrown out and the surface rubbed over with a brush of tow
to equalize the coating; and if not satisfactory the operation must be
repeated. The vessels usually tinned in this manner are of copper and
brass, but with a little care in cleaning and manipulating, iron can
also be satisfactorily tinned by this means. The vessels to be tinned
must always be sufficiently hot to keep the metal contained in them
thoroughly fused. This is covering by contact with melted tin.
The amalgam process is not so much used as it was formerly. It
consists in applying to the clean and dry metallic surface a film of a
pasty amalgam of tin with mercury, and then exposing the surface to
heat, which volatilizes the latter, leaving the tin adhering to the
metal.
The immersion process is the best adapted to coating articles of brass
or copper. When immersed in a hot solution of tin properly prepared
the metal is precipitated upon their surfaces. One of the best
solutions for this purpose is the following:--
Ammonia alum 17-1/4 oz.
Boiling 12-1/2 lb.
Protochloride of tin 1 oz.
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