Sapphire crystal Glass made of artificially produced sapphire. It is very hard (9 on the Mohs scale) and scratch-resistant. It ranks just below the diamond in these two respects.

When Lange's engineers develop a movement, they have a straightforward objective: They want to create a technically exceptional accomplishment, a useful instrument, something that is without precedent. And they also want the movement to be peerless from the aesthetic point of view. After all, it will be visible through a | sapphire-crystal caseback some day. A movement first sees the light of day in the studio of the prototype builders. They craft every single new part by hand, a process which takes a great deal of time. They look at it from the point of view of manufacturability, they analyse its mechanical strength, and after assembly, they investigate how it performs in terms of functionality inside the mechanism for which it was made. All design details are optimised in close co-operation with the members of the engineering team. This sequence of designing, testing, optimising, and renewed testing is continued until the entire movement runs flawlessly. As a rule, the design phase lasts for several years.