Cobalt Driers may be added to oil and alkyd colours, oil mediums and drying oils in recommended measured quantities.
Cobalt Driers are known as ‘surface’ siccatives (driers) and will only speed the drying of the surface of the paint film. They are not ‘through-film’ siccatives and do not perform as successfully with thick films of oil (i.e. impasto technique)
Langridge recommends that Cobalt Driers should be added to an oil medium or artists’ drying oil rather than mixed directly into the oil paint. Measuring quantities of driers directly into small amounts of colour is difficult and prone to miscalculation.
Langridge recommends addition to mediums and oils to reduce the likelihood of over use and to simplify the artists’ studio practice. Once mixed with an oil or medium, the artist can dispense with concerns about constant ongoing additions of driers.
Add Cobalt Driers as an approximate 1% addition. (i.e. To 500ml of Linseed Oil add 5ml of Cobalt Drier.) Shake or stir well together. When initially mixed together, the driers will impart a blue/green cast to the oil or medium with which it is mixed. Exposed to indirect sunlight for a few days will remove this colour difference (Exposing the oil or medium to indirect sunlight will not sun bleach or thicken the material). If used in correct proportions, the colour of the cobalt drier will not interfere with oil paint brightness or colour saturation.
Driers made from lead, manganese and other proprietorial mixtures that do not wholly contain cobalt driers are to be avoided as they promote darkening and loss of flexibility. However, even Langridge Cobalt Driers are to be used sparingly as its over-use will destroy paint films.