The principle of heat transfer is illustrated in the video bellow. The temperature in the tip of the flame of a candle is around 1,500 °F (816 °C). A balloon coming in contact with the flame will burst, because heat is transferred from the flame to the thin surface of the balloon increasing its temperature (heat content). However, if the balloon if filled with a certain amount of water, the heat from the flame will not build up on the balloon’s surface because it will be transferred to the water, which in effect acts as a heat sink preventing the balloon from bursting!
This is an awesome art form: painting with live organisms! For this the laboratory techniques of the microbiologist are adapted by artists to "paint" using multicolored bacteria as pigments and a solid agar surface as a canvas. The challenge is that your "brushstrokes" are barely visible initially. To fully see your work you need to allow the bacteria to grow. You can either use natural strains of bacteria, or you can use organisms that have been genetically modified to make them produce the desired colors. The whole procedure is explained in the video below.
Art from the lab of Roger Tsien. Picture by Paul Steinbach. Used under an Attribution-Share Alike 3.0 Unported license.