It's frustrating when something's clever but you don't know exactly how it's clever. The ceramic Vortex Salt & Pepper Shakers, designed by
a Frankfurt-based team of ID'ers using digital manufacturing by Shapeways, fit that bill perfectly: Each has only one opening in the top, which is how you load them. But when you invert them to dispense, only a measured pinch of salt or pepper escapes.
So how did they do it? Presumably there are some tricky, possible-with-digital-manufacturing-only channels inside the container that we'll never get to see, unless we buy one of these just to break 'em open.
Says the design team, who collectively go by the handle Moloko,
[Looks] simple—but getting it right was tricky. Because designing a salt and pepper shaker for Shapeways has two big constraints: the design rules for hollowed ceramics demand an opening with a diameter of at least 10mm—but there is no food safe material available on Shapeways to make a plug for this hole.
So we had to come up wih a one-piece plugless solution: This shaker is conveniently filled from the top, through it's big funnel-shaped opening. Obviously nobody wants all of the stuff to fall out again when using the shaker. We created a really simple but effective retaining system that lets the shaker be filled easily but keeps the condiment inside when you turn the shaker upside down. Only a pinch of condiment will leave the shaker when shaking it slightly, just like it should be.