Thanks all for the suggestions. I managed to clean it quite well with very hot water and soap. Took me ages - as soon as I pour the hot water out of the mould to start wiping the melted wax immediately dried before I could start wiping . Also my mould is cylinder (polycarb), quite narrow so I can't quickly stick towels in it to wipe clean. All that cleaning was after rustic which came out really nice. Now last night I attemted marble (turned out ridiculous, as expected - I poured too cold+ too much colour). Now that cold pour made a real mess so I have to try the oven. I hope it will be ok as this is my only mould so far...