I'm a children's pastor in Bowling Green, KY. I nned to build two 5' tall lava lamps. Does anyone know if you could use acrylic tubing for the body of your lamp? Like a 1/4"thick x 7" diameter acrylic tube.
You need to look at the spec sheets to see what temperatures Acrylic can withstand. The lava itself probably never runs hotter than 70 degrees Celsius, but the chamber containing the bulb may very well be much hotter. I'm not sure if plastic is right for the job. You will need something hard and strong, but even the hardest plastics become softer as the temperature increases. Your project may warp or leak over time. I can tell you that silicon glue would be perfect for sealing the container. It is durable, clear, and although somewhat rubbery, it is extremely strong, and best of all, it is rated up to 400 Fahrenheit.
Also, you'll spend a fortune gathering and fine-tuning the chemicals necessary to make the lava flow, with no guarantee that it will operate properly when assembled.
If you want a really huge Lava Lamp, you could save yourself some trouble and buy a colossus. The pricetag is a whopping 1000 dollars, but it is four feet tall and the globe by itself weighs 100 pounds. Since it is an official product, you are guaranteed something that works well and will last. There are a variety of color combos and base styles available. If you want two of them, a yellow/purple and a yellow/blue would probably complement each other very well. The url is: http://www.lavacolossus.com/