watch manufacturers make use of many materials in the production
of watch cases. We believe the following information about case
materials and finishes will be of practical help for the consumer.
The case (together with the glass, the bezel and the strap) has
two functions : Protection of the movement against impurities, water
and shocks and external aspect which gives the watch its own personality.
Extract from the trilingual "Lexique
du Génie Horloger"
The following presentation shows the characteristics
of the main materials used in the production of watch cases.
Stainless steel on its own or combined with a yellow metal is certainly
still the most popular material for the cases of quality watches.
Steel is a tough material which does not deteriorate if knocked
or scratched. It is an alloy (iron and carbon) that can be given
a good polished finish and it does not corrode.
The cases of gold-plated watches are shaped out of a base metal
like brass and then dipped in a bath where a layer of gold is electro-deposited
on them. The thickness of the layer of gold on a swiss gold plated
quality watch will normally be 10 or 20 microns (10 to 20/1000 of
a millimetre). Gold-plating of this thickness should remain in good
condition even if it is subject to a certain amount of friction,
for instance from a shirt cuff. As perspiration can damage goldplating,
the backs of quality gold-plated watches a normally made of stainless
Platinium used in watch cases is a fairly hard precious metal with
a silvery-white colour and is unexpectedly heavy to those not accustomed
to handling objects made form it. It does'nt oxidize by high temperatures.
Clearly the best known precious metal used in watches cases is gold.
In addition to its value, gold has the advantage of keeping its
colour and not oxidizing. Gold is a soft metal and has to be alloyed
to other materials. Naturally the higher the gold content, the more
valuable the case is. The gold content is quoted in carats or "karats",
with 24 carats equalling 100% gold. One gold carat means 1/24 gold
in the alloy. 18 carats means that that 18/24 of the alloy consists
of fine gold. The colour of gold depends on the metals with which
it is alloyed (gold, silver, nickel, copper, palladium) : the final
colour will be white, yellow or rose gold.
Form time to time manufacturers introduce collections of silver
watches. Tarnshining is a problem with this precious metal as it
needs to be polished regularly to keep its shine. However, forms
of surface treatment have been used in an attempt to overcome this.
The silver content is quoted in thousandth : in Switzerland, the
legal quotes are 925/1000 and 825/1000.
Titanium is an exciting space-age noble
material. It is particularly prized for its very high strength/weight
ratio. Although its price is up to 10 times more expensive than
stainless steel and is costly to machine, it offers distinct benefits
when used in watch cases : titanium is antimagnetic, it does not
cause allergies and is anti-corrosive. It is light, rigid, chemically
neutral and non-toxic. Titanium has a velvety pearl-grey colour
and texture which changes with the light. The scratches no longer
stand after a few days.
In recent years several Swiss quality watch manufacturers have adopted
new materials in the form of hard metals made from soft metallic
tungsten or titanium carbide powder. Cobalt is added to this powder.
The powder is pressed into a shape, sintered and heated up to a
very high temperature (1300 to 1500°C). The resulting shell is machined
and finally polished with diamond tools. The end-result is a very
hard and very highly polished case resisting scratches and keeping
its fine initial appearence.
Rhodium and chromium-plated
Rhodium is a rare metal, rather hard, highly reflective used to
plate lower-priced watches. It looks more or less like platinium.
It is harder than the base metal it is used to coat. Chromium is
a white metal that is also used to coat lower-priced watch cases
so that they resist rut and wear.
During the manufacturing process, cases can be given different kinds
of finish. For instance, they can be polished to give them a mirror-like
shiny surface. They can be given a brushed finish, in which the
surface is marked with very thin parallel straight or circular lines
or lines in the form of spirals. These all are decorative effects.
The latest kind of finish is described as "shot-blasted" or "micro-balled".
The case is held under a very fine
jet of minuscule glass balls which bombard the surface and give
it a special mat effect.
There are of course other materials than these presented above used
in the manufacturing of watch cases, such as aluminium, wood, rubber,
granite, ceramic, plastic. These cases, mostly fashion oriented,
have all their own manufacturing processes and characteristics.