Colloidal glass colouring
To understand what colloidal colouring of glass means, we first have to look at the term "colloidal" itself. It contains the Greek word for glue. And indeed: Colloidal colouring does involve this.
It refers to particles which are finely dispersed within a medium, but able to move freely. Now let us look at colloidal glass colouring. It is based on metallic salts which are added to the glass batch. Initially they have no effect at all and the glass seems to remain a neutral colour.
It is only the subsequent annealing of the glass that allows the metal particles, which were practically stuck beneath the glass surface before, to release, grow and develop the desired colour effect.
Initially the particles absorb the incoming light. The larger the colloids, the more intensive their colour effect. Colloidal coloured glass is also known as "ruby glass", the pure and true ruby glass.
The type of metallic salts added to the glass batch determine the colour which the glass will have to the human eye. Of course the amount of salts also have a decisive influence on the colour.