Each wall of the Obelisk Vase is composed of a voronoi network. However, unlike standard voronois - tessellations that typically form around randomly distributed points - the points here flow in a gradient, from sparse on the top to dense on the bottom. This allows the lower third of the vase to be watertight.
There's also a subtle accompanying gradient of tube diameter, which likewise runs from slighter on the top to thicker on the bottom. This helps shore up any remaining holes and also lends a bit more gravity to the base.
While it's impossible to imagine that this gradient effect has not been exploited before, I've never seen it. After a few years of searching for a piece that makes use of this effect, I decided to make one myself. I'm quite pleased with the result; to me, it's reminiscent of the vines that wind up temples in the rainforest.