Mediums

What is a medium?

To make a paint with a pigment, you have to mix it in what is called a medium. This medium is a liquid, creamy or gelatinous substance. When drying, the medium turns more or less solid to form a film.

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The mediums of the Old Masters

In Europ, from antiquity till about the 9th or 11th century, the most utilized medium for painting was hot wax. This method is known as encaustic painting.

A new technique appeared during the Middel Ages and became the predominant one in the 12th century: the egg-yolk tempera. The origins of this technique remain uncertain. But it was utilized, among others, by the Italian and Flemish Primitives. The tempera medium is a mixture of egg-yolk and water, thus a very lean medium, i.e. containing no oil at all. This characteristic is essential.

The freshness and the vivacity of color of the works of these Old Masters is to be attributed to this lean manner of painting ¹. But it remains a rather limited technique that prevented them from obtaining smooth gradations of color, which are easy to realize when painting in oils.

In oil paints, the medium is a mixture of linseed oil with other substances like turpentine, white spirit, resins and siccatives.

One of the secrets of the first painters who largely utilized oil colors, the brothers Johann and Hubert Van Eyck at the beginning of the 15th century ¹, was to begin a picture in the same way and with the same materials than the primitives, i.e. with an egg-yolk emulsion, and to finish the painting in oil, particularly with oil glazes.

Painting in pure oils, without tempera underpainting, was rather uncommon before the 16th century. It’s only during the 16th and the 17th centuries that oil became the prevalent painting medium.

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The new emulsions

At the beginning of the second half of the 20th century, there have been appeared new emulsions, particularly the vinylics and the acrylics. Contrary to the egg-yolk emulsion, which becomes harder and more rigid with age, these new emulsions always remain as supple as rubber.

In theory, this is not an advantage for the underlying dead-painting on supple supports like canvas before an upperpainting in oil, because the oil film turns hard and brittle with the time, particularly if the oil medium contains hard resins like copal — what was very common until recently. When you have a brittle film on flexible layers, there’s every chance that cracks and splits will appear. OK: that’s the theory, but in the practice, until now, when the oil film contains no hard resin, nobody has noted this phenomenon.

On a rigid support, it’s quite another situation. The flexible layer acts as a buffer whichs isolates the movements of the wood from the more or less rigid oil film. Now this flexible layer prevents to some extent splitting and cracking of the oil picture.

Until recently, some people regarded as hazardous to paint with oils on a too flexible underground, like canvas prepared with acrylic emulsions. Nevertheless, there exists now since some decades an oil medium which remains supple and resilient when drying: oil-modified alkyd resin, a combination of an alkyd resin and soya oil (less yellowing than linseed oil, what is another advantage).

On the other hand (and above all if the support is rigid), the use of a synthetic white primer covered by a synthetic watery emulsion underpaint becomes an advantage for ordinary oil painting, because the rule of “fat over lean” is perfectly followed, what is the best way to prevent the formation of cracks ¹.

In addition, the combined emulsion and oil technique will produce a painting that will keep up its colors better than any other one painted entirely in oil, because the emulsion underpainting, contrary to an oil underpainting, will have no tendency to yellow or darken with age.

With the passing of time, we can judge better the qualities of the modern resins. We know now that paintings in acrylics, made fifty years ago, are still as fresh as the first day and have absolutely not yellowed, what should certainly not have occurred if they were painted in oil.

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My mediums

For about 15 years, I have painted my dead-paintings with a modern synthetic watery emulsion, which permits an easier expression of the artist than the old egg-yolk dispersion of the Primitives.

Nevertheless, there are some things impossible to render with emulsions and it is thus usually necessary to carry on the work with oils.

For some years, I have painted the first layer in oils with an alkyd medium — above all because it’s less yellowing than linseed oil (See Trials, Mediums). Then I carry on the following layers with an oily medium which is my secret ¹ because it’s precisely the core of the technique of the old Flemish Masters.

The final glazings in oils give the painting a subtle tone quality impossible to render with other means. Beginning in waters and finishing in oils is precisely the method employed by the Old Flemish Masters, particularly the Brothers Van Eyck, to give their works that extraordinary brightness that has stood the test of time.

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