Alexander Watt Electroplating & Electrorefining (1889)
The great progress which has been made in the production of
artistic casting in iron has always created a desire that
some economical and reliable method of coating such work
with copper could be devised, not alone to preserve the iron
from atmospheric influence, but also to enhance the beauty
of the work by facing it with a superior metal.
To deposit a protective coating of copper upon large pieces
of cast iron has been a matter of considerable difficulty
owing to the almost inevitable presence of sand holes and
other flaws. Since these defective spots do not receive the
deposit of copper, the underlying metal must always be
liable to corrosion when subjected to the effects of
moisture.
To overcome these difficulties M. Oudrey at his works in
Auteuil, France does briefly described:
The cast iron object is first coated all over with varnish
composed of resinous
matters dissolved in benzol, to which is added a sufficient
quantity of red or white
lead, the varnish then allowed to dry. The surface is then
brushed over with
plumbago and the article then coated with copper in the
ordinary sulfate bath by
the "single -cell" method. In about 4-5 days a sufficiently
thick coating of copper
is obtained. After rinsing and drying a bronzed appearance
is given by the
application of a solution of ammonio-acetate of copper.
All the lamp - posts of the city of Paris, the beautiful
fountains of the Place de la
Concorde and of the Palace Louvois and a considerable number
of statues and
bas-reliefs have been coppered at Auteuil by M. Oudrey.
It is obvious that in the above process a quantity of copper
is used far in excess needed for a protective coating on
iron. It is also clear that since the copper represents
merely a thin shell that a very moderate amount of rough
usage such as the Parisian " gamin" or a London street Arab,
by the simple process of climbing the lamp posts with metal
tipped boots, would quickly break the shell and expose the
underlying layers of plumbagoed varnish.
THESE OBJECTIONS CONSIDERED, THIS METHOD OF COPPERING IRON
DOES NOT APPEAR TO HAVE MUCH TO RECOMMEND IT. IN COPPERING
CAST IRON, AN ALKALINE CYANIDE METHOD WOULD BE PREFERRED.
One of the chief reasons why alkaline Coppering solutions
seldom work well is that they are prepared with cheap
cyanide containing but a small percentage of the real
cyanide and overloaded with carbonate of potash, a salt
which has no solvent action on the anode.
A good coppering solution to be worked in the cold could be
prepared as such:
( It is essential to use cyanide of good quality)
1. 3 oz of chloride of copper to each gallon of solution
required is dissolved in a 1 1/2 pints of cold water.
2. 12 oz of soda crystals are next dissolved in a quart of
water
3. The soda solution is added to the chloride of copper with
gentle stirring after each addition. The resulting carbonate
of copper is allowed to settle. After an hour or so, the
supernatant liquor is poured off and fresh water added to
wash the precipitate; decant and rewash twice.
4. The precipitate is then dissolved in a solution of
cyanide of potassium composed of 6 oz of the cyanide in
about 1 quart of water.
5. Water is added to make up one gallon.
THIS SOLUTION WILL COAT CAST IRON VERY EASILY WITH A CURRENT
FROM TWO TO THREE DANIELLS IN SERIES.
