The larger the piece is, the longer the time required for this process. In general, it takes about 20 hours before the fused piece is ready to be removed from my kiln. The COE means that the glass heats and cools at the same predictable rate. Without this feature, different pieces of glass could not be fused together, they would shatter. Adding different metal oxides to sand, soda and lime, the basic formula for glass creates different colors.
Light blues require copper, while dark blues require very small quantities of cobalt.
Amethyst glass contains manganese. Opaque white can contain either tin or calcium. Selenium is one metal oxide that is used to produce reddish colors. The information on color in glass is derived from the web page on colors at the Corning Museum of Glass web site. The finished product has more than one color, and the different colors can be seen when the glass is viewed from different angles.