Watching the paint dry

[Gus]

I've noticed a lot of Natural Pigments paints will dry considerably quicker than say a Cadmium color and the addition of an earth color in a mixture will speed the drying. Is what I notice just because there is more oil in some paints? Could there be a chemical reaction or something in Earth colors? George has mentioned salts.
Thank you.

[George O'Hanlon]

I've noticed a lot of Natural Pigments paints will dry considerably quicker than say a Cadmium color and the addition of an earth color in a mixture will speed the drying. Is what I notice just because there is more oil in some paints? Could there be a chemical reaction or something in Earth colors?

Just to be clear, are you saying that you have noticed that many Rublev Colours Artists' Oils dry faster than cadmium oil colors?

To understand the different rates of drying for oil colors, let's consider some basic factors that affect the rate at which drying oils, such as linseed oil, set and cure ("dry"):

First, it is important to understand that each pigments absorbs a different amount of oil, or rather we can say that each pigment requires a different amount of oil to make a paste of the same consistency (viscosity). This has a major effect on the drying time of the color. For example, 100 grams of basic lead carbonate (lead white) requires 10 to 15 grams of linseed oil to form a paste. The same amount of lampblack requires at least 100 to 150 grams of oil.

Second, pigments often react with the oil and especially the free fatty acid content of the oil, forming metal soaps. This, too, has an effect on the drying time. Lead, copper and cobalt-based pigments often react with the free fatty acids in oil forming various metal soaps.

Third, some pigments slow the autoxidation rate of drying oils. Lampblack, which is composed almost entirely of pure carbon, acts as an antioxidant, slowing down the drying rate. Other pigments can have similar reactions with oil, such as cadmium sulfide and mercuric sulfide (vermilion), and hence the slow drying rate often observed for these pigments.

Fourth, some modern additives often used in artists' oil colors can cause paints to "puff" or the oil incorporated in the paint to increase viscosity. This sometimes requires that more oil be added to make the same consistency in paint that does not contain these additives, such as Rublev Colours Artists' Oils.

[John Kennedy]

Also, remember that modern paints, when manufactured use extenders and various fillers, such as brighteners and thickeners, amoung other ingredents. Rublev Artist Oils are pure pigment and oil, with no additives to alter there natural state. Earth pigments are just what they say they are, EARTH and each pigment has its own natural characteristics in oil, and each one preforms differently, based on oils absorbsion. Hope this is helpful. Also, you can read more about oil paints in the Natural Pigments Catalog. If you don't have one George will send you one.