Rubber strapsTheir high-end quality is a perfect match for the casual elegance that characterises Longines watches

EXCEPTIONAL PROPERTIES

Moulding rubber straps offer excellent mechanical, aesthetic and chemical

properties. Their high-end quality is a perfect match for the casual elegance

that characterises Longines watches. The versatility of the manufacturing

process also means that the straps can be made in an array of colours

and surface finishes.

COMFORTABLE AND LONG LASTING

Genuine rubber is comfortable to wear and is both FDA- and BgVV- approved,

meaning that it complies with the most stringent of standards governing

biocompatibility and skin contact. Under normal conditions of use, rubber

straps last for an average of 18 months. They can, however, age prematurely

when exposed to the stresses of urban life or to excessive sunshine.

FLEXIBILITY AND RESISTANCE

Genuine rubber is heat-treated with sulphur or other elements in a process

known as vulcanisation, designed to increase the resistance of the rubber

yet preserve its elasticity. It is different from natural rubber, which is made

from latex collected from rubber trees and renowned for its cushioning

properties, and from thermoplastic elastomer (TPE), which is halfway

between vulcanized and plastic rubber.

Swiss Super-LumiNova®

Since timepieces have been in existence the question of telling the time in the dark has constantly occupied watchmakers

For a long time solutions were limited to repeater mechanisms, candles

or an open dial which allowed the hands to be touched with the fingers.

With the onset of the First World War the urgency of solving this problem

became paramount. Watchmakers of the time remembered the great

discovery made at the end of the 19th century: radioactivity, where by the

luminescence of radium was an important aspect. And it was this characteristic

that was used in the watchmaking industry for many years, but later abandoned

in favour of tritium owing to the high level of radioactivity in radium. Used

until the 1990s, tritium also proved to be radioactive, but at a much lower

level than radium. Tritium was then replaced by Swiss Super- LumiNova®,

a material that has the same practical use as tritium, but is not radioactive

and thus more environmentally friendly.

There is a fundamental difference between Swiss Super-LumiNova® and

tritium- based luminescent substances. The latter are permanently stim-

ulated by electrons (betarays) that tritium emits when it spontaneously

transforms into helium. It is for this reason that it remains luminescent for

several years, even in total darkness. In contrast, Swiss Super- LumiNova®

needs to be stimulated by violet or ultraviolet light. After being “charged”

in this way it emits a more intense luminescence than tritium which grad-

ually fades after a few hours in darkness, however.

THE PRINCIPLE OF LUMINESCENCE

Luminescence is produced when the electrons in a molecule or a crystal

are stimulated by an external energy source. This can be ultraviolet light

(“black light”), a biochemical reaction (as in the glow-worm) or radio-

activity, but not heat. The electrons thus stimulated normally return to their

original state very quickly by emitting radiation, sometimes in the form of

visible light. In the case of Swiss Super-LumiNova®, the energy emitted

by the electrons is stored at a relatively stable level, which results in light

being emitted over a period of several hours.