Glass objects can be coloured in two ways: certain ingredients can be added into the metal to change its colour, or glass can be painted after it has become cold. Glasses painted with enamel colours are can be brilliant works of art. Poor-quality glass with impurities often has a green or brown tint by nature, and this is why the finest glass vessels were always made of completely clear glass. However, these vessels were often decorated with coloured glass (e.g. beautiful blue was used), but it was always dyed separately for each purpose
