Message 32562 of 39188 in General Discussion

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Somewhat in relation to this demonstration, but also just in general...

Does anyone know what it takes to get solid, clear, ice in large lumps from a 
domestic freezer?
I've tried a few times over the last week to see if there was a secret I was 
missing. I'm freezing tap water in 1 litre yogurt containers. Slightly tapered 
so i guess it has room to expand if needed, but it keeps coming out mostly 
opaque or cracked.

In the interests of experimentation I've been trying additives to see if 
there's a household ingredient that'll make a difference. A tsp of sugar, a 
tsp or vinegar didn't work. I know salt'll make it cloudy.

Is there some chemistry school trick anyone knows? Is it better to freeze slow 
or fast? Stir it in the middle? 

.dan.

[edit]
Heh, I should have started with Google.
http://www.edgerton.org/resources/kidscorner/kidscorner/clearice.html

Apparently distilled water + boiling + mild agitation and slow bottom-up 
freezing are all good factors.