In order for decorations made of melted chocolate to set up hard and shiny, the chocolate used to make them must be “tempered,” meaning that it’s within a specific temperature range when it’s poured or shaped. Chocolate that’s out of temper when shaped has a streaky gray appearance, sometimes referred to as “bloom.” The method used to make the bands for the Chocolate Mousse Layer Cake is a quick and generally reliable way of tempering chocolate, but you may want to use a thermometer to double-check that the chocolate is at the proper temperature before pouring it. As long as you don’t scorch the chocolate, you can reheat and cool it as many times as necessary to get it in temper.
Temperatures for tempered chocolate
Bitter- and semisweet chocolate: 88° to 91ºF
Milk and white chocolate: 84° to 87ºF