The auxiliary products are indispensable mediums for modifying the characteristics of the colours. The Vallejo Mediums can be divided into five categories: Gessos for the preparation of the painting grounds, mediums for modifying or binding the colours, Special Mediums developed for changing the properties of the colours or delaying the drying time, various Transparent Gel Mediums and Opaque Textures which add volume and body to the colours. The auxiliary products are waterproof, they do not yellow and are resistant to ultraviolet.