While chatting with Nick the other evening I remarked that the crystals on Bremonts were so clear that they were almost invisible. Mine is over a year old and does not have a scratch. I had handled an IWC Flieger chronograph 'pre owned' and had noticed that although the crystal itself was not scratched the AR (anti reflective) coating was very scratched and made the crystal look blue.

Nick casually remaked that Bremonts don't scratch like that because they have 9 coats of AR. WHAT?????

9 coats, front and back? So how many does the Flieger have that I saw? Really this IWC really needed the crystal repoacing becasue teh AR coating made the crystal look ruined.

This is the kind of information we need, very cool indeed!

Wikipedia return for 'AR coating'.

Anti-reflective or antireflection (AR) coatings are a type of optical coating applied to the surface of lenses and other optical devices to reduce reflection. This improves the efficiency of the system since less light is lost. In complex systems such as a telescope, the reduction in reflections also improves the contrast of the image by elimination of stray light. This is especially important in planetary astronomy. In other applications, the primary benefit is the elimination of the reflection itself, such as a coating on eyeglass lenses that makes the eyes of the wearer more visible, or a coating to reduce the glint from a covert viewer's binoculars or telescopic sight.

Many coatings consist of transparent thin film structures with alternating layers of contrasting refractive index. Layer thicknesses are chosen to produce destructive interference in the beams reflected from the interfaces, and constructive interference in the corresponding transmitted beams. This makes the structure's performance change with wavelength and incident angle, so that color effects often appear at oblique angles. A wavelength range must be specified when designing or ordering such coatings, but good performance can often be achieved for a relatively wide range of frequencies: usually a choice of IR, visible, or UV is offered.

Single lens coatings were invented in November 1935 by Alexander Smakula, who was working for the Carl Zeiss optics company. Anti-reflection coatings were a German military secret until the early stages of World War II Ώ]. They were independently invented by Katharine Burr Blodgett in the late 1930s.