Saw this done on the TheBackyardScientist’s youtube channel https://www.youtube.com/watch?v=KdpQo3tRPLY and gave it a go myself. Not having to worry about filming, I just just put the water beads in a plastic trash can (with a bit of aluminium plate at the bottom to stop it melting through).
Step one is get a little furnace going.
I made one from a steel bucket and a mixture of cement/sand/lime, with refractory cement applied around the inside.
Unfortunately I didn’t leave enough space for a self drawing burner, so I just stuck a hair dryer on it and force feed propane that way.
It doesn’t take too long to melt, once it gets warmed up. I have a 500ml and a 1500ml crucible, just simple steel ones since the furnace will not get hot enough to melt these.
Step two is set up the water beads (actually step one since they take a few days to swell from a 2mm ball to a 25mm one).
I found it worked a lot better when the water was drained out as it slowed the passage of the aluminium. However, this required the setup be hosed down straight after the pour so the beads don’t cook and smoke.
Reasonably quick pour seemed to work the best for longer pieces, while a slow pour made them more shallow.
Cleaning them couild be trick, might see how they weather for a bit. Possibly try and acid wash or beadblast.