Drying Rates

(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)

Each pigment affects the drying rate of its oil vehicle differently.  Some speed the oxidation process, some slow it down, and some have no effect at all.  To compensate for this, most manufacturers add a small amount of drier, such as cobalt or manganese, to the slowest‑drying colors.  This narrows the range of drying times within a line of paint, but, even with these driers, some colors’ drying times may differ from others by several days to several weeks.

As mentioned above, natural and synthetic resins can be used to narrow the range of drying times further.  Winsor & Newton accomplished this in its alkyd paints by using an oil‑modified alkyd in which it grinds its pigments.  The Schmincke Company and has narrowed the range of drying times by using a resin‑oil formulation specific for each pigment in its Mussini paint.  Blockx, by using a small amount of amber.  However, these paints are unique.  Most other brands of oil paint have a large gap in drying time between certain colors and caution in their combined use may be necessary.

A faster‑drying paint should never be applied over a slower‑drying paint; otherwise cracking is a likely result.  Some of the slowest‑drying colors not rec­ommended for underpainting are all carbon‑based blacks (ivory, lamp, carbon, and charcoal black), all cadmium‑based paints (cadmium red, cadmium yellow, cadmium green), vermilion, alizarin crimson, zinc white, and Vandyke brown.  These colors, unless modified by the artist or the manufacturer with a drier or resin, can take between three and five days in a thin paint film to dry.

Among the faster‑drying colors are the cobalt‑based colors (such as cobalt yellow, cobalt blue, and genuine aureolin), manganese‑based colors (manganese blue, manganese violet, and manganese black), raw and burnt umber (both contain large amounts of manganese), Prussian blue, and lead‑based whites and colors (including flake white, cremnitz white, Naples yellow, chrome red, and chrome yellow).  Some colors, such as the manganese‑based colors, have a strong cata­lytic effect upon drying oils and are often ground into poppy oil in order to slow the drying time.

Each manufacturer does or does not adjust the drying rates of its colors according to its own idiosyncrasies, and do not supply information about the drying times or the film characteristic of their colors.  An understand­ing of the nature of specific pigments, combined with knowledge of the pigments used by a manufacturer to produce a particular color, will help you to infer a drying rate.  Clearly this requires some research, but when you consider that most artists establish a palette of twelve to eighteen colors and vary it only slightly over the course of their careers, it would seem to be a small effort for a lifetime investment.

In addition to modifying drying times through the use of media, a painter can accomplish the same goal by mixing slow‑drying colors with fast‑drying colors.  One of the reasons artists by genuine cobalt violet, usually the most expensive color you can buy, is not only for the incredible violet color it possesses, but because you can take small bits of this color and mix it into other colors to speed the drying time with little affect on the appearance of the color.

 

(Excerpts from ART HARDWARE: The Definitive Guide to Artists’ Materials, by Steven Saitzyk © 1987 revised 1998)