Glass is a very durable material. Glass does not change colour or bleach, and tolerates moisture. If it is not mechanically damaged, future generations may also benefit from performed works. In theory, glass is frozen plasma that flows in time due to gravity, but this phenomenon can be witnessed only over a period of hundreds of years. (E.g. the glass windows of old churches are thicker below.) However, there are certain technological tricks for the prevention of the consequences of this phenomenon. To add decorativeness and privacy, the glasses are opacificated, covered with decorative films or back-painted. The latter is executed with glass toughening process with special heat resistant paints. Safety film keeps the shattered glass together and prevents slivers from flying around in case of an accident. Contemporary glass constructions are easy to maintain with modern means and these can also be covered with water-repellent glass wax, as a result of which stains from dried water on glass are now history.