You need to stamp onto white tissue paper and colour in etc. Then using greaseproof paper place the image on the candle cover with the greaseproof and hold it tight. Using your heat gun heat until all the 'white' of the tissue disappears and smooth out with your fingers, careful, don't get burnt. The greaseproof coating on the paper will help 'melt' the image onto the candle. You shouldn't be able to see the edges of the tissue when it is done HTH