Coloured scanning electron micrograph (SEM) of cut foam glass. This building material is made by heating a mixture of crushed or granulated glass and a blowing agent such as carbon or limestone. As the glass melts the blowing agent releases a gas, forming bubbles in the glass. When cooled the glass has a rigid cellular structure. Foam glass is fireproof, waterproof, non-toxic, corrosion-resistant, non-aging, insulating and light-weight. Magnification: x120 when printed at 15cm wide.