The special 288-facet Jacob-Cut Diamond is a feature of the Astronomia collection. There is only one vendor in the world that can produce this patented cut and they are based in Israel. Here are the steps in its creation:
The Jacob-Cut diamond starts out as a rough diamond more than twice the finished stone's size. First, a rough diamond big enough has to be found, and the purity, clarity, and color has to be of the highest quality both inside and out, and there can be no inclusions. If they start to cut the diamond and find an inclusion, the entire piece will be ruined.
Next, the diamond is cut by machine into a round shape, close in size to the final diamond.
Then, the gem cutter shapes the stone by hand, cutting each individual facet (of 288). This has to be done slowly and carefully, as the stone has to be perfectly round and symmetrical. The danger is that the stone will become oblong and not round. To be used in the Astronomia Collection, the Jacob-cut diamond has to be completely round and weigh exactly as much as the other three satellites (time display, triple-axis tourbillon, magnesium globe).
During the process, if the gem cutter puts slightly too much pressure while adding the facets, too much of the diamond will be cut away, and will end up smaller than the desired diameter. The cutting process takes at least two weeks of dedicated, painstaking work.
To make the final one-carat, Jacob-cut diamond with 288 facets, more than half of the initial rough diamond will be cut away.
The complexity of cutting the 288 facets by hand and making sure everything is symmetrical and the diamond is absolutely round, is what makes the Jacob & Co. diamond used in the Astronomia collection so special.
The Jacob-cut diamond rotates on itself in 30 seconds, while traveling around the dial in 10 minutes.