Oil paint is a slow-drying paint, that consists of particles of pigment suspended in an oil, which is most commonly linseed oil. To change the viscosity of the paint a solvent like turpentine or white spirit and varnish can be added to increase the glossiness of the dried film. Oil painting technique is mostly preferred due to its richness of color and the texture the paint produces on paper. However, novice painters face the problem of judging the drying time of this paint. As one of the practical properties of this paint is that it takes a long time to dry. These paints can take several weeks to dry, and hence an artist needs to paint in many sessions while working on an artwork. But, due to its propensity it allows very subtle blending of color. Also, this medium allows to produce vivid color with a natural sheen and distinct contrast. Oil paints also have a surface translucency which is similar to human skin, that makes it an ideal medium for painting portraits.
The drying time of a paint color depends on the pigment that is contained within the paint, for example, titanium white dries slowly because it is derived from titanium oxide.
Whites: Shades of white like zinc and titanium can take 5 or more days. Shade of white which is flake is rapidly drying paint and can dry in a period of 2 days.
Blacks: Black color mars is fast drying and takes around 2 days to dry. Black lamp and ivory are slow drying and can take 5 or more days.
Yellows: Yellow cadiums and hansa can take around 5 or more days. Yellow shades like ochre and mars take around 5 days to dry. Shades of yellow like naples, cobalt, and Indian yellow are rapidly drying colors that take around 2 days time. Yellow-red shade which is cadmium orange is also a slow-drying paint that takes around 5 or more days.
Reds: Shades of red used for painting which are cadmium and alizarin have exterior oil paint drying time around 5 or more days. Shade of red mars takes around 2 or more days.
Earths: Shades of Earth which are siennas and umbers are fast-drying colors that take 2 days to dry.
Purples: Shade of purple which is manganese is a fast-drying paint that takes around 2 days to dry. Other shades of purple like cobalt violet and mars take 5 days to dry.
Blues: Many shades of blue dry fast and just take 2 days time to dry such shades are cobalt, manganese, phthalo, and Prussian blue. Other shades like ultramarine blue and cerulean blue take around 5 or more days to dry.
Greens: Shades of green like viridian and terre verte fall in slow drying time for oil paint, which is 5 or more days. However, shade of green which is phthalo is a fast-drying oil paint that takes only 2 days time to dry.
You can add few drops of drying oil to your oil color to speed up the process of drying. However, the drying oils may change the shade of the paint, so be sure to add them before you start painting, instead of adding the drying oils to your paint colors halfway.