The lava-lamp wax sinks on cooling, so the surrounding liquid must have a density a little less than 0.9. Ordinary alcohol (ethanol) has a density of about 0.8, and a 40-50 per cent aqueous solution would have a density that could be adjusted to just below that of paraffin wax. The solid wax would then sink.
Now you know what to pack for Bora Bora you can get started. When you are done, weigh your bags. Luggage allowance for Air Tahiti inter-island flights is 20 kg/45 lb per person and strictly enforced (due to plane size). Divers may have 5kg extra. Carry on hand luggage is 3 kg/6.6lb. See more absolutely 'must know' info about flying to Bora Bora to ensure smooth Bora Bora travel.
Keep in mind also that the overhead space on the Air Tahiti (inter-island) flights has very, very small compartments so that anything larger than a small bag will be checked. I carry my camera and electronic devices (iPad, etc.) in my purse so their weight isn't included in my carry on bag.