A Painting Secret Hidden for Six Centuries

Varnish Inside the Painting: Why Did Van Eyck Place a Clear Layer Between Glazes?

Jan van Eyck’s 1439 Portrait of Margareta van Eyck, also known as Margaret, the Artist’s Wife, contains a surprising secret. Conservators found varnish not only on the surface, but also between two of the final layers of red paint.

Van Eyck may have considered the portrait nearly finished, applied varnish to make the colors richer, and then changed his mind. After seeing the colors fully revealed, he appears to have added one more transparent red glaze to deepen the shadows of the dress.

A glaze is a thin, transparent or semi-transparent layer of paint. Instead of hiding the paint below, it modifies its color. Glazes can deepen reds, soften transitions, and create rich shadows without making them opaque.

The evidence comes from an examination conducted after the Groeningemuseum in Bruges lent the portrait to the National Gallery in London. The technical account was written by conservator Jill Dunkerton, with research contributions from Rachel Billinge, Rachel Morrison, and Ashok Roy.

Researchers examined a tiny paint sample from a damaged area at the lower edge of Margareta’s dress. Viewed from the side under a microscope, this cross-section revealed the sequence of materials.

Under ultraviolet light, scientists distinguished three red glazes. Between the final glaze and the one beneath it was a strongly fluorescent, unpigmented layer. Old oils and natural resins can glow under ultraviolet light, while pigmented paint usually fluoresces less strongly. The position of the clear layer proves that it was present before the last glaze was applied.

The layer is a confirmed fact. Van Eyck’s intention cannot be proved. Dunkerton proposed that he varnished the nearly finished portrait to saturate its colors. He may then have decided that the folds in the lower right corner needed greater depth and added another glaze. That final glaze remained glossy and saturated, so it may not have needed another varnish coating.

Why would varnish help? As oil paint dries, some passages can become dull or “sink in.” Dark areas may appear lighter and weaker than they did when wet. A clear coating reduces the cloudy effect caused by light scattering across a dry surface. Colors look deeper, darks become more unified, and the artist can judge the painting more accurately.

The dress is a lesson in layered painting. Van Eyck began with a thin, opaque layer of vermilion over a white chalk ground. He modeled the folds with transparent red lake glazes. Laboratory analysis identified kermes, an expensive dye obtained from scale insects, and madder, made from a plant. Their binding medium was heat-bodied linseed oil, gently heated to alter its working properties.

For the deepest shadows, Van Eyck added bone black and natural ultramarine. Researchers could even see that he had blotted the sticky glaze with his fingers or palm to distribute it evenly. His painting looks impossibly refined, yet his methods were direct and physical. The wider scientific context for these materials is explained in the National Gallery Technical Bulletin.

Another clue appears on the back of the panel, which was painted to imitate polished stone. Scientists also found a transparent layer there between colored applications. The glossy coating on the reverse consists mainly of heat-bodied linseed oil with a small amount of pine resin. The researchers suggest that a similar oil-resin material may have been used on the front.

This does not mean that painters should put modern finishing varnish between paint layers. Fifteenth-century coatings differ from many modern removable varnishes. Paint applied over varnish may not adhere securely. Future cleaning also becomes difficult because a solvent that removes varnish might disturb the paint above it. A scientific review in Heritage Science explains how solvents can affect oil paint.

For beginners, the most valuable lesson is not a secret recipe, but Van Eyck’s way of thinking. He built color gradually, observed how each layer changed as it dried, judged the overall effect, and returned when something needed adjustment.

Glazes cannot rescue weak drawing or incorrect light and shadow. They work when the structure underneath is convincing. Make test samples, observe how colors change after drying, and learn the difference between opaque paint and transparent glaze. Great painting grows from patient observation and carefully judged decisions.

For beginners, the most valuable lesson is not a secret recipe, but Van Eyck’s way of thinking. He built color gradually, observed how each layer changed as it dried, judged the overall effect, and returned when something needed adjustment.

At Old Masters Academy, we pay close attention to the methods of the great masters, including Jan van Eyck. We study how they prepared their paintings, built form through carefully organized layers, and used transparent glazes to create depth, richness, and luminous color.

You do not need rare fifteenth-century pigments or historical varnish recipes to learn from these methods. Traditional painting principles can be successfully adapted to safe and reliable modern materials. What matters most is understanding how to prepare the foundation, when to use opaque paint, how to apply transparent glazes, and how each new layer affects the painting beneath it.

Become a member of Old Masters Academy and learn how to paint using the time-tested methods of the Old Masters. Follow a clear, structured program, develop your skills step by step, and turn your ambition to become an artist into a real and achievable journey.

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