Hipstomp at the Core77 blog writes:
In some of Manhattan’s better Japanese-staffed bars, like Tribeca’s underground B-Flat, ice cubes are noticeably absent; ordering your scotch on the rocks gets you a large ice sphere. With less surface area than the same amount of ice rendered in cubes, a globe of ice will melt more slowly, keeping your drink cold without making it watery.
As an industrial designer, your correspondent couldn’t help but notice the parting line on B-Flat’s ice spheres; after all, it has to come out of a mold. But now a company called Taisin has come up with a clever device for making a perfect ice sphere with no parting line.
How does it work? You sandwich a large chunk of ice in between the two metal pieces pictured above. As the ice slowly melts, gravity brings the top half to close over the bottom half, enclosing what ice remains in its spherical cavity. Because the ice is in the process of melting into its new shape as the top closes, there’s no parting line. Clever!