VIII. STIPPLING
Also called
spotting, stippling is a type of decoration that is fairly
widely used on bridges, bars, plates, recesses and dials.
This operation reproduces circles made up of extremely close or
even overlapping concentric lines.
The hand-made method
This decoration is achieved using a circular-graining lathe. The
flat end of a wooden or rubber peg around 2 mm in diameter, driven
by a belt or a bow, revolves carrying a damp mass of abrasive
powder.
The pattern is formed by bringing the revolving stem into contact
with the stem which marks the surface of the part at regular intervals.
Quality circular-engraving must be regular and this type of decoration
is extremely hard to achieve and calls for expertise and tremendous
control. The abrasive used must be chosen in accordance with the
desired depth of decoration and must be changed regularly if one
wishes to maintain the depth initially chosen.
The industrial
method
Industrial circular-graining machines are still fairly rare and
extremely expensive; they are numerically controlled and are suitable
for large series. The result is regular, but the parts are strictly
identical and do not enable the kind of personalisation one obtains
from manual methods.
IX.
GUILLOCHE WORK
OR ENGINE-TURNING
Guilloché work is a pattern consisting of geometrical motifs engraved
on the surface of the part.
These may be extremely varied patterns made up of interwoven lines
creating a decorative result. It is a combination of straight
and circular lines which was extremely popular in the early 19th
century.
The complexity of this work and the skill required have meant
this type of decoration is reserved for extremely expensive watches.
Currently, prestige brands wishing to decorate their cases or
dials with guilloché work or engine-turning have to seek out and
restore extremely rare antique machines.
Guilloché
work: methodology
First of all, the surface of the part must be particularly well
prepared, since the guilloché work would otherwise be distorted.
The part is prepared by smoothing to achieve the best possible
polish, before using a finishing paste in order to highlight the
mark of the guide during the guilloché work itself.
A final polish than provides the final radiance desired. It is
essential that the burin by perfectly filed, sharpened and adjusted
according to the material used and the desired depth in order
to give a sharp and shiny cut which will be suitable all processes
where polishing is not needed.
When a polished finish is required, as guilloché cases, the edges
of the burin must be painstakingly polished. Thus sharpened, the
burin will give the brilliant and polished cut appropriate for
high-end watches.
The burin must also be placed at the correct height to avoid distorting
the guilloché pattern.
The number of waves on the engine-turned circle and the motif
are a question of personal choice.
The craftsman ensures that the part is placed perfectly flat to
ensure that the guide remains in equal contact with the surface
of the part around its entire rim.
See: Bevelling
and finishes...(VIII)
