Hourglasses are a cool and ancient timekeeping technology.
Now, I posit that they developed when someone held a handfull of sand and let it drain through the bottom of their fist... the curled little finger.
So, I'd like an hourglass in which each bulb is fist shaped (in negative space) so it appears the sand is draining through it in this (with sand filling the top bulb to make the shape clear). The exact proportions would need to be tuned so that it looks good with sand filling the top, but not looking silly as it fills the bottom, as well as the exact shapes so that sand is never trapped by cups in the top bulb
See also Wikipedia:Hourglass