Striking colours: When glass gets hot and blushes
Glass in its pure form is clear and transparent. Colours are created by chemical processes, after adding additives to the liquid glass and annealing the finished glass. Experts refer to this process as "striking".
The glass takes on a colour during the annealing process. Annealing is a heat treatment to bring the glass to a certain temperature. And this is how it works: First, the glass is melted. In this case, it remains colourless, though. The annealing process begins afterwards.
The glass changes colour. Different colours develop depending on the intensity of the annealing or heating process. This is due to microscopically small chalcogenide crystals, usually with added cadmium. These increase or grow as the annealing process continues.
You could say that this process turns the amorphous structure of the glass into an ordered, crystalline structure. This process for colouring glass is called "striking", a targeted change of the structure and therefore a targeted change in colour. As a rule, glass with striking colour has a very sharp colour edge.
This makes it ideal for use as filter glass. It gets interesting when this glass is now processed with modern laser technology. This creates an exceptional colour array.