Historically, watchmakers used rare precious stones like diamonds, rubies, or sapphires. The latter two are both naturally-occurring colored variants of the mineral corundum. Today, many movements make use of synthetic corundum. The stones are aluminum oxide, and the differing tones are a result of adding certain elements. Red corundum stones most frequently serve as jewel bearings in watch movements. The color of these so-called synthetic rubies is analogous to that of true rubies. However, the color is optional and some brands opt for transparent bearings instead, including Moritz Grossmann. It’s now probably occurred to you that the sapphire crystal protecting countless dials is none other than colorless corundum. Since jewels…