How do you date a painting? Technique, layers and style

A painting is dated by combining three kinds of evidence. The material: what it is painted on (wooden panel or canvas), how the canvas is stretched and which pigments are present, since many colours have known years of invention. The technique: how the layers are built up, from ground to varnish. The style and subject: composition, clothing, hairstyles and objects. A material often gives an earliest possible date, not an exact year, and a reliable dating requires examination by a conservator.

Facts

What this guide can and cannot do

This guide describes how art historians and conservators go about it, so that you can understand a painting better and ask the right questions. It cannot determine who painted a picture or what it is worth, and the app makes no such assessments. If you have a painting that you believe to be old or valuable, turn to a conservator, a museum or an auction house that can examine it in person.

The basic idea is simple. A painting can never be older than its youngest material. If you find a pigment invented in 1830, the picture cannot be from the 18th century, however old it looks. Conversely, old materials prove nothing about the age of the painting itself; a forger can use an old canvas.

Step 1: what is it painted on?

Turn the painting over. Until the 16th century almost all pictures were painted on wooden panels, in the north often oak and in Italy often poplar. The Mona Lisa is painted on poplar, and van Eyck's Arnolfini Portrait on oak. In the 16th century canvas took over, first in Venice, because it was lighter and could be made larger. For oak panels there is a method of its own, dendrochronology: the annual rings are compared with known series and give a year at which the tree can earliest have been felled.

How the canvas is stretched also says something. Older canvases were nailed to a fixed frame. Stretchers with wedges in the corners, so that the canvas can be tightened later, became common in the second half of the 18th century. In the 19th century colourmen began to sell ready-made canvases with stamps on the back, and such a stamp can be dated fairly precisely.

Step 2: the layers in cross-section

An older oil painting is built up in layers, and the diagram below shows them from the support upwards: a ground of chalk or gesso, sometimes a coloured imprimatura, an underdrawing, an underpainting in grey or brown, the paint layer itself, thin glazes and, on top, varnish. The order and the materials changed over time. Italian painters primed with gesso, northern Europeans with chalk, and in the 17th century dark, reddish-brown grounds became common. How fresco and tempera are built up compared with oil is described in the guide to fresco, tempera and oil.

With infrared photography the underdrawing can be seen through the paint and changes, known as pentimenti, can be discovered. In this way it has been seen that in the Arnolfini Portrait van Eyck changed several details. X-rays show heavy pigments such as lead white and can reveal an entirely different picture beneath the surface. Ultraviolet light makes varnish fluoresce and shows where someone has retouched later. See Looking at art: techniques and the words in the glossary, for example pentimento, glaze and grisaille.

Step 3: the pigments

Many colours have a known year of birth, and they are therefore the best evidence. Prussian blue was discovered in Berlin in the early 18th century and soon became popular; if it is found in a painting said to be from the 17th century, something is wrong. Cobalt blue came in the early 19th century, synthetic ultramarine in the late 1820s and zinc white as an artists' colour in the 1830s. Before that ultramarine had to be made from the expensive stone lapis lazuli, which Vermeer used in Girl with a Pearl Earring; read more in the guide Rembrandt and Vermeer.

In the 20th century came titanium white and synthetic organic pigments, and after the Second World War acrylic paint. The invention of the paint tube in the 1840s made it easier to paint outdoors, which the Impressionists took advantage of. Pigments are identified with a microscope and with analyses that do not harm the picture, but this requires a laboratory.

Step 4: style, subject and clothing

Once the material has given a framework, style helps to narrow down the date. How is the picture composed? Is there linear perspective, soft transitions, strong contrasts, visible brushstrokes? Every period has its characteristics, and the app's period pages describe them. Also read the guide How do you read a painting?

Clothing and hairstyles are often the most exact evidence in portraits, since fashion changed quickly: ruffs, wigs, wide skirts, narrow trousers. Objects in the picture give an earliest date, such as a certain kind of furniture, an instrument or a book. The symbols may have changed meaning over time; see the guide to iconography and attributes.

Pitfalls: varnish, signatures and copies

Old varnish yellows and darkens, and then a painting looks older than it is, or entirely different. The Night Watch got its name when the varnish had darkened so much that people thought the scene took place at night; it does not. Craquelure, the network of cracks in the paint, can arise naturally but can also be induced with heat.

Signatures and dates may have been added later, by a dealer who wanted to raise the value. Copies and workshop replicas were made openly in every age, and a copy can be old and still not be the original. A single piece of evidence therefore carries little weight; it is when material, technique and style point the same way that a dating becomes credible. The same method is used for furniture; compare with the design section's guides on dating an antique chest of drawers and dating an antique chair.

What you can look for yourself

Exercise

You find Prussian blue in a painting said to be from the 17th century. What does it mean?