For many years, the peak of luxury watchmaking saw timepieces that were richly clad in gold, titanium or platinum. There was considerable value attached to the weightiness of a watch, even if its very heart — the movement — was kept hidden from plain sight, destined to spend years whirring away in the darkness. 

While these watches still make up a large part of the industry’s offerings, a handful of watchmakers have gone against the grain to offer something unheard of decades ago: Sapphire crystal cases. Like skeletonised watches, these bare everything for all to see, only their inner workings are now visible from all angles and not just from the top down.

It’s one way of showing off a firm’s proficiency in craftsmanship, but sapphire crystal cases are also regarded as the height of watchmaking savoir-faire because of the technicality involved. As the second-hardest naturally occurring material on earth (next to diamond), sapphire crystal requires diamond-tipped tools to carve and polish. The process is reportedly so painstaking that even the tiniest of flaws would require starting over. More than 200 hours are usually poured into making these pieces of art, which explains why they’re almost always limited editions.

Below, a list of the most show-stopping watches with sapphire crystal cases.