Take 100 parts playground sand, 35 parts washing soda and 15 parts potassium carbonate - mix and grind together well in the trusty pestle and mortar. About 15 mins of grinding.
Prepare your kiln - A couple of flowerpots, one inside the other, fill with crushed barbecue charcoal.
Embed in this a ceramic crucible with lid and put you mixture in it. Cover and add more charcoal to cover the crucible.
Microwave on full power for 30-40 minutes.
Take care as it will be extremely hot, well over 1,000ยบ, when you remove it. Allow it cool and retrieve your batch.

Seen on one of those weird late night TV science programs.