I recently did a little research for a customer question and thought I would share it.
Cobra is faster drying overall and all the colours dry in the same amount of time. Cobra contains added driers to make all the colours dry at the same rate. Artisan does not have added driers and this means each colour dries at a different rate, some pigments are fast drying and some are slow drying. Driers are usually only added to student-grade colours but Cobra is an artist-grade colour, so it is a bit unusual.
Cobra oil colour has a uniform drying time and degree of gloss. Depending on the thickness of the layer, it will be dry to the touch in 3-5 days. This is much quicker than traditional oil colours.
Information on the Cobra website.
Winsor Artisan has the same drying time as Winsor’s Artist Oil Colour and their student colour Winton. After the water has evaporated it is the same as their regular oil colour.
As with traditional oil colour, Artisan colours have different drying rates.
Here is a list of the drying rates of pigments on the Winsor & Newton website.
Fast drying – around 2 days
Prussian Blue, Umbers.
Medium Drying – around 5 days
Cadmium Hues, Phthalo Blue (red shade) and Phthalo Greens, Siennas, French Ultramarine, Synthetic Iron Oxides, Ochres, Titanium White, Zinc White, Lamp Black, Ivory Black.
Slow drying – more than 5 days
Cadmiums, Permanent Rose (Quinacridone), Permanent Alizarin Crimson.