What are the two liquids that make up a lava lamp?

• The complete list of ingredients in the "Lava-lamp" is a company secret, but they are, fundamentally, coloured wax in coloured water. Invented by Edward Craven Walker in 1963, the idea originated from a wartime egg timer, and progressed into the Pop classic, the Astro lamp. The lamps are still produced today by the original company, Mathmos.

  The lamps work using a bulb in the base of the lamp (underneath the bottle) which heats the contents until the wax becomes molten. It then slowly rises to the top of the lamp, where it cools slightly, and sinks back to the bottom. This process is repeated, creating the unique shapes in the water.

  Ruth Bonser, Mathmos, London EC1.

• I think that Ruth Bonser of Mathmos is being somewhat misleading in saying that her "company secret" is "fundamentally . . . water". The floating globules in my daughter's lamp are obviously wax and look to have properties very much like normal paraffin or candle wax, rather than dense waxes, such as sealing wax. Paraffin wax has a relative density of about 0.9. 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. On warming, the wax density falls substantially (more so than the ethanol) so it would then float.

  When lit, the dyes in the solution glow with a fluorescent luminosity. Most common fluorescent dyes are substantially quenched in pure aqueous solution, but exhibit fluorescence in ethanolic solution.

  Roger Moore, Newport Pagnell, Bucks.

• In Northern Ireland we have our own version of the lava lamp known as the "Port of Doom Apparatus". This contains an orange and a green liquid of equally thick consistency and proportion. As the orange material attempts to return through a narrow capillary referred to as the "Garvaghy Constriction", the equally dense green liquid refuses to be dislodged from its alcove. This results in a permanent state of agitation at the interface of the two compounds, with copious amounts of fetid hot gasses periodically belching into the environment. A third liquid of separation prevents the primary fluids from making actual physical contact, thus avoiding a chemical meltdown.

  During the summer months the lamp heats up, becoming highly volatile. The gaseous outpourings increase, the orange liquid in particular swells considerably and sometimes flaming particles can be seen shooting around vigorously at the constriction point. This is a source of great interest and confusion to external observers not familiar with the workings of the lamp, but of much discomfort to those of us who live in the vicinity. Persistent lamp watchers, far from being calmed, inevitably develop a glazed expression, a furrowed brow and a catalogue of psychological problems identified as the "Drumcree depression".

  Name supplied, Belfast.

• Kitsch and schmaltz?

  David Vickery, Croydon

• My daughter got one as a gift. The liquid is pinkish orange. The thing which supposedly have lava resemblance looks more like floating human body part and pieces of flesh from horror movie. It's terrible.

  Balet, Chicago USA

• The main liquid.. distilled water with a couple of drops of dish washing liquid,then added a spoon of pickling salt(pure). If the wax stays at the bottom when hot, add a little more salt, a little at a time, until the wax flows. Too much and the wax will stay at the top. You add food colouring for colour. Wax density = Candle wax.

  KuK, Ipswich England