another surface took on its under side an accurate impression of
that surface, even to the scratches on it, and three years later
Jacobi, of St. Petersburg, and Jordan, of London, applied the
method to making copies or replicas of medals and woodcuts. Even
non-metallic surfaces could be reproduced in copper by taking a
cast of them in wax and lining the mould with fine plumbago,
which, being a conductor, served as a cathode to receive the layer
of metal. It is by the process of electrotyping or galvano-
plastics that the copper faces for printing woodcuts are prepared,
and copies made of seals or medals.

Natural objects, such as flowers, ferns, leaves, feathers,
insects, and lizards, can be prettily coated with bronze or
copper, not to speak of gold and silver, by a similar process.
They are too delicate to be coated with black lead in order to
receive the skin of metal, but they can be dipped in solutions,
leaving a film which can be reduced to gold or silver. For
instance, they may be soaked in an alcoholic solution of nitrate
of silver, made by shaking 2 parts of the crystals in 100 parts of
alcohol in a stoppered bottle. When dry, the object should be
suspended under a glass shade and exposed to a stream of
sulphuretted hydrogen gas; or it may be immersed in a solution of
1 part of phosphorus in 15 parts of bisulphide of carbon, 1 part
of bees-wax, 1 part of spirits of turpentine, 1 part of asphaltum,
and 1/8 part of caoutchouc dissolved in bisulphide of carbon. This
leaves a superficial film which is metallised by dipping in a
solution of 20 grains of nitrate of silver to a pint of water. On
this metallic film a thicker layer of gold and silver in different
shades can be deposited by the current, and the silver surface may
also be "oxidised" by washing it in a weak solution of platinum