Engineering: When you need to stir something that is less dense than your solvent.

Finally, we can use this approach to make multimaterial structures as well. By controlling where infusion and/or precipitation happens, you can spatially control the formation of the filler.

Here, we only grew the iron oxide on the top surface of the spring! (7/8)

But what's fun is that you can use this approach to grow all kinds of nanoparticles. You just need to adapt the infusion-precipitation conditions appropriately.

Here, we grew two kinds of fillers. We first grew iron oxide and then silver, which is why it appears silver but is magnetic (6/8)