Celebrating Time-Honoured Crafts 2 - The ElectroPlater
By: Kong : May 23rd, 2011-09:52
The electroplating workshop looks very much like an alchemist’s
laboratory. Its function is to change brass into gold… or something
similar. It actually works by in using electrolytic processes to apply
layers of metal to parts that are out of metal themselves in order to
protect and embellish them. An electroplating workshop is therefore
first and foremost a set of liquid vats serving as containers for
coating, washing and rinsing.
The parts arrive there from the
decoration workshops of Chopard Manufacture in Fleurier, where the L.U.C
watches are made. They have been treated to a wide range of finishes
including bevelling, circular graining, hand drawing, Côtes de Genève
and engraving. Some of them – such as the tourbillon bridge – have been
the object of many hours of craftsmanship, and their cost price is so
high that their handling and treatment call for extreme care. Therfore
meaning the electroplating specialist cannot afford to make any
mistakes.
The parts are mostly in brass, a metal that tends to oxidise
over time or simply by being touched. They will thus need to be
protected by a stainless metal, which is why gold and rhodium are ideal
because of their air resistance.
To begin the cycle, the plates
and bridges are first hung onto cone-shaped current-conducting racks.
These funny-looking “Christmas trees” are first immersed in solutions
designed to eliminate any traces of grease, starting with a
grease-moving solution reinforced by ultrasound waves, followed by a
simple soapy water bath, and then an electrolytic bubble bath.
The
electrolytical baths are conducted at a voltage of 7 to 10 volts,
whereas the amperage and the duration are both determined by the total
surface area to be treated. Between each immersion, the components are
rinsed in clear water and then in purified water – meaning water from
which all mineral salts have been removed. Once this washing process is
completed, the parts are soaked in an electrolytic “activation” bath, an
extremely acid solution (with a 0 pH) intended to neutralise any trace
of soap and to “activate” their surface, meaning to make it more robust
to receive and retain a layer of metal.
The first “plating” bath is
designed to deposit a layer of nickel that serves as an additional
barrier against corrosion and also to facilitate the adherence of the
finishing layer. Next come the colouring baths as such, in which four
gold colours – 5N, 4N, 3N, 2N – and two rhodium colours – white and
black – are available. In quantitative terms, these metallic deposits
are only “flashes” a few tenths of a micron thick, but they will give
the part its final colour.
Once this stage is complete, a last
degreasing and a final “activation” operation is performed. After being
rinsed in pure water and dried, the parts have acquired their definitive
appearance and are ready to be sent to the workshop of the watchmaker
who will assemble them.