Wim L. Noorduin […] dissolved barium chloride (a salt) and sodium silicate (also known as waterglass) into a beaker of water. Carbon dioxide from the air dissolved naturally into the water, fomenting a reaction to form barium carbonate crystals. In response to the crystals the pH of the solution surrounding them lowers, triggering a reaction with the dissolved waterglass, and adding a layer of silica to the growing structure. This reaction uses up acid from the solution and allows the barium carbonate crystals to continue to form.
As this process takes place, the shape the crystals take can be manipulated through changes to the solution–increases in carbon dioxide levels in the water creates “broad-leafed” structures. Reversing the pH gradient at the right moment can create curved, ruffled structures. "You can really collaborate with the self-assembly process," said Noorduin.