egindele

PureTime sells a number of different models of the GMT II. Which one did you buy?

Having worked for a number of years in the business of manufacturing large space-based telescope optics, I was surprised to learn that watches have AR coatings at all. We always considered the AR coating on glass to be fragile to abrasion - more fragile than the glass substrate. The simplest coating, but least effective from the anti-reflection performance perspective, is SiO2 ref The Mohs hardness for SiO2 is 7 which is better than for glass (6.5) but less than for sapphire (9). This means that coating a saphire crystal with SiO2 would have about the same abrasion resistance as a glass crytal. Better AR performance can be achieved with multi-layer coating designs. I have more experience with these multi-layer designs which is probably why my impression of AR coatings equates to fragility. The multi-layer coating designs would be more approapriate for the inside of the crystal. Here is another reference on coatings ref Personally, I'm not as interested in watches with double AR coatings because I wouldn't expect the outer coating to last. Scratches in the outer AR coating can not be polished out the way glass can. However, an AR coating on the inside surface of a crystal should last a very long time. The inner surfaces of SLR lenses are AR coated and last for many years. I think the best explanation for why Rolex doesn't use AR coatings is that they haven't in the past. I also don't accept the longevity argument. Rolex charges about $750 to refurbish a watch which includes polishing the plastic crystals they have sold for years.

Thanks. The avatar I found by googling for "modern dance".

I agree. The Moissanite rings look fantastic. To my eye, the CZ and the Moissanite materials are excellent. However, since Moissanite currently sells for 100's of time what CZ sells for, they are typically in expensive settings. CZ on the other hand is so inexpensive that they are typically mounted in very cheap settings. The early tests, and the least expensive in terms of test equipment, is using electrical conductivity. Moissanite is most likely an insulator like diamond. The more sophisticated tests use ultra violet light. It is even more difficult to test for a synthetic diamond. As such, the synthetic diamond manufactures have agreed to etch their name in the stone.

I purchased 100 1ct CZ stones from Thailand. Here is the link: http://www.syntheticgems.org/

A about a year ago, I spent several months researching diamonds, sapphires, and other gems. This was prompted by my daughter