The ability to create an in-house tourbillon movement is immensely valued in the world of horology, which is why Armin Strom decided to celebrate its premier caliber of this kind with no less than four versions of the watch, each named after an element. Just like Water version we have previously reviewed, Earth (with the reference number ST 13-TE.90) is supplied with the mentioned proprietary ATC11 caliber with an 18 K white gold lever and the distinctive architecture that places its balance wheel and seconds pinion on the same axis. Naturally, there are likewise some differences between the versions. Earth model features decorations that correspond to this element, while its case is made from stainless steel with black PVD treatment which gives the earth-like tone to the housing.
As it could have been expected, the fifth and so far the most intricate manufacture caliber by Armin Strom, ATC11, is actually the focal point of the collection and each of the four versions. To make it visible as much as it is possible, the Biel-based company made it available through both sides of the case; not only that it can be seen through the exhibition case-back, but also through the skeletonized segments of its off-centered black face. The caliber in question is 16 lignes wide (36.6 mm) and 6.2 mm thick; it has an escape wheel and pallets made from solid gold, while the regulating system of choice is screwed balance with Breguet spiral. Beating at the frequency of 18,000 vph, it includes 184 parts and 24 jewels. Thanks to its double spring barrels, once it is fully wound by hand, the caliber offers quite an impressive power reserve of 240 hours. The mentioned element-inspired decorations are featured on the baseplate and the tourbillon bridge.
Not that different from the other versions, Earth tourbillon still features some idiosyncrasies. For example, these are a black chapter ring with founded appliqués, a black PVD steel housing and a genuine black alligator horn-back leather strap (which fastens with a double-fold clasp) and an additional rubber band (which is likewise in black). On the other hand, the features that this model shares with the others are case dimensions of 43.4 mm x 13 mm, the presence of glare-proofed sapphire on both sides, as well as water resistance of 50 meters. Moreover, this watch is also available in a limited edition of 50 copies, just like the other watches from the Tourbillon collection by Armin Strom.