[kenneth]

Why is top down easier? I have a few "neat ice kit" which does that for ice cubes for drinking, but the results are very mixed.

I've always wondered why it's a top down design instead of a bottom up? It seems to me like if you were to freeze a container bottom up, the impurities would be pushed out towards the top, and eventually out of the water into the air above, instead of making bulging shapes as ice expands and wasting half your ice with trapped impurities.

I should test the theory later at home.

[somacert]

Mainly mechanical

Top down you can put the the water in a small ice chest and the insulation will slow the freeze in the bulk. otherwise it freezes outside in

That ice floats may play some role, I am not sure if for or against.

I made a couple of attempts, just for fun, and found the ice chest necessary but never made a systematic study of the process.