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Page 16
BLACK PAINTS.
Carbon, in one form or another, is the base of all black pigments. By
far the most common of these, as used in structural plants, is
graphite. Other black pigments are lamp-black (including carbon black)
and bone-black, the former being produced in many grades, varying in
price from twopence to half a crown per pound. Bone-black, which is
refuse from the sugar-house black, varies in the percentage of carbon
contained, which is usually about 10 or 12 per cent, the remainder
being the mineral matter originally present in the bone, and
containing 3 or 4 per cent of carbonate, whilst most of the remainder
is phosphate of lime. Lamp-black is an absolutely impalpable powder,
which having a small amount of greasy matter in it, greatly retards
the drying of the oil with which it may be mixed. For this reason it
is not used by itself, but is added in small quantity to other paints,
which it affects by changing their colour, and probably their
durability. For example, it is a common practice to add it to red
lead, in order to tone down its brilliant colour, and also to correct
the tendency it has to turn white, due to the conversion of the red
oxide of lead into the carbonate.
BLACK STAIN FOR IRON.
For colouring iron and steel a dead black of superior appearance and
permanency, the following is a good formula: 1 part bismuth chloride,
2 parts mercury bi-chloride, 1 part copper chloride, 6 parts
hydrochloric acid, 5 parts alcohol, and 50 parts lamp-black, these
being all well mixed. To use this preparation successfully--the
article to be blacked or bronzed being first made clean and free from
grease--it is applied with a swab or brush, or, better still, the
object may be dipped into it; the liquid is allowed to dry on the
metal, and the latter is then placed in boiling water, the temperature
being maintained for half an hour. If, after this, the colour is not
so dark as is desired, the operation has simply to be repeated, and
the result will be found satisfactory. After obtaining the desired
degree of colour, the latter is fixed, as well as much improved
generally, by placing for a few minutes in a bath of boiling oil, or
by coating the surface with oil, and heating the object till the oil
is completely driven off The intense black obtained by this method is
admirable.
Another black coating for ironwork, which is really a lacquer, is
obtained by melting ozokerite, which becomes a brown resinous mass,
with a melting-point at 140� F. The melted mass is then further heated
to 212� F., the boiling-point of water. The objects to be lacquered
are scoured clean by rubbing with dry sand, and are dipped in the
melted mass. They are then allowed to drip, and the ozokerite is
ignited by the objects being held over a fire. After the ozokerite has
burned away, the flame is extinguished, and the iron acquires a firmly
adhering black coating, which resists atmospheric influences, as well
as acids and alkalies. If the black iron vessels are to contain
alkaline liquids, the above operation is repeated.
A good cheap stock black paint or varnish for ironwork is prepared, as
follows: Clear (solid) wood tar, 10 lb.; lamp black or mineral black,
1-1/4 lb.; oil of turpentine, 5-1/2 quarts. The tar is first heated in
a large iron pot to boiling-point, or nearly so, and the heat is
continued for about 4 hours. The pot is then removed from the fire out
of doors, and while still warm, and not hot, the turpentine, mixed
with the black, is stirred in. If the varnish is too thick to dry
quickly, add more turpentine. Benzine can be used instead of
turpentine, but the results are not so good. Asphaltum is preferable
to the cheap tar.
To make another good black varnish for ironwork, take 8 lb. of
asphaltum and fuse it in an iron kettle, then add 2 gallons of boiled
linseed oil, 1 lb. of litharge, 1/2 lb. of sulphate of zinc (add these
slowly, or the mixture will boil over), and boil them for about 3
hours. Then, add 1-1/2 lb. of dark gum amber, and boil for 2 hours
longer, or until the mass will become quite thick when cool. After
this it should be thinned with turpentine to the proper consistency.
VARNISHES FOR IRONWORK.
A reliable authority gives the following as a very good recipe for
ironwork varnish. Take 2 lb. of tar oil, 1/2 lb. of pounded resin, and
1/2 lb. of asphaltum, and dissolve together, and then mix while hot in
an iron kettle, taking all care to prevent the flames getting into
contact with the mixture. When cold the varnish is ready for
application to outdoor ironwork. Another recipe is to take 3 lb. of
powdered resin, place it in a tin or iron vessel, and add thereto
2-1/2 pints of spirits of turpentine, which well shake, and then let
it stand for a day or two, giving it an occasional shake. Then add to
it 5 quarts of boiled oil, shake it thoroughly well all together,
afterwards letting it stand in a warm room till it gets clear. The
clear portion can then be drawn off and used, or reduced with spirits
of turpentine till of the requisite consistency. For making a varnish
suitable for iron patterns, take sufficient oil of turpentine for the
purpose of the job in hand, and drop into it, drop by drop, some
strong commercial oil of vitriol, when the acid will cause a dark
syrupy precipitate in the oil of turpentine, and continue to add the
drops of vitriol till the precipitate ceases to act, after which pour
off the liquid and wash the syrupy mass with water, when it will be
ready for use. When the iron pattern is to be varnished, it must be
heated to a gentle degree, the syrupy product applied, and then the
article allowed to dry.
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