that´s really easy....
You need a piece of clear plastic or polycarbonate.
Take a candle and melt drops of wax onto the surface in irregular pattern .
Paint the part where you want to have the ice black .
Before you fix the plastic you need to plane the wax .
Take a hot iron ( Bügeleisen ) and a greaseproof Paper ( Backpapier ) , and plane the wax carefully .
Now you can fix it .
One thing i forgot ....dont burn the candle , melt it anyway else ....
If you burn it , the wax gets grey or Black .....and it looks more like Marmor .Also useful for Floors .
Sorry , missing some english words .
That´s really easy , IF I CAN , YOU ALL CAN .... try it .
I will do one and make some Pictures of the work in process .