Pearl cut
The pearl cut is a cut pattern or pattern to decorate surfaces. Other names are in French perlage or perlée and the German sparkle , dotting , cloud touches , partridge eye (French. Oeil-de-perdrix ) or peacock eye pattern .
Manufacturing
For production, small, circular surfaces are repeatedly ground by a rotating tool compared to the surface of the workpiece. The tool is lifted completely and regularly offset by a certain amount - typically precisely the radius of the circle - before it is pressed down again for grinding to create the next circular surface. The surface of the workpiece is completely covered by sufficient overlap. A pattern is created by the geometry of the feed, for example line by line like text, but with overlapping gaps like honeycombs. The pattern can be strictly regular and extend over the edge of the workpiece or it can follow the contour of the flat or curved piece - e.g. B. clock cover, container cap - orientate. The feed of the tool axis can be done manually or it can be automated.
Creation of the reflex image
Each circular area is made up of essentially concentric, groove-shaped grinding tracks with a clearly irregular profile. The width, depth of the grooves and the steepness of the flanks vary. A smooth surface of an object generally reflects light from a point source at only one point on that surface into the image-taking eye of a viewer. With increasing roughness, this reflex point on the object increases and loses its brightness. At other points on the object, only randomly matching groove flanks reflect light from the source to the eye.
If the area spanned by the 3 points light source Q, eye A and the object point G under consideration intersects the object surface in G at a right angle, then those groove pieces that lie on the narrow diametrical sectors of the circular disk that are parallel to the intersection line of the 2 mentioned areas reflect selectively . This applies to all object points along the cutting line.
At other points on the object, pairs of sectors pointing in other directions shine. Just switching from one eye to the other changes the picture somewhat. Moving the viewer, the light source or tilting the object causes the apparent rotation of the brightly perceived sectors of all circles. Due to the effect of the overlapping of the ground circles, one of the sectors of each circle is cut off.
The distinctive pattern of the resulting image impression and the movement of the light sectors clearly cover any scratches or scuff marks that may have been incompletely sanded over on the material.
Application in watchmaking
Nowadays the pearl cut is mainly used in the manufacture of wristwatches in the course of the finishing of the work plate , the inside of the watch case back , the bridges and the cocks . The circular grinding pattern is applied either manually or precisely controlled using rotating abrasives . A single polished point is called a pearl. Under normal circumstances, pearl-cut surfaces in watchmaking are invisible because they are inside the watch. The pearl cut is therefore more likely to be found as a luxury element in high-quality watches. With skeleton watches and watches with an open dial , these decorations are visible without opening the case back.
In addition to the pearl cut, other cut patterns and techniques have also been developed, e.g. B. False ribs, ribs, stripes, peacock's eye, cubes, diamonds, circular stripes, circular ribs, sun and false circular ribs.
Application in vehicle and container construction
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Much larger grinding points than in clockmaking were used in historical vehicle construction on railway wagons or car dashboards. For example, the area under the windows of the Bundesbahn's n-car was pearled over a large area; this made smaller bumps less visible because the surface was no longer reflective. However, the stainless steel is now hidden under paint on the cars that are still in use today. As a homage to this time, the dashboard of the Bugatti Veyron 16.4 was decorated with pearl cut. Stainless steel tanks, for example for milk, beer and other food or drinks, often have a polished peacock eye pattern.
Web links
- Clockwork ornaments (English)
- Perlage as oeil-de-perdrix pattern (English)
Individual evidence
- ^ GA Berner: Illustrated specialist lexicon of watchmaking (electronic version), keyword 'pearls'. Retrieved November 9, 2012.
- ↑ GA Berner: Illustrated specialist lexicon of watchmaking (electronic version), keyword 'Perlung'. Retrieved November 9, 2012.
- ^ GA Berner: Illustrated specialist lexicon of watchmaking (electronic version), keyword 'ornamentation'. Retrieved November 9, 2012.