Can a painting be dated using carbon-14 dating?

The answer is yes, but only partially. We can only date the organic materials it is made of, such as canvas, wood, or paper. We cannot date the pigments, and it is sometimes difficult to date the varnish.

The scientific approach based on materials is transchronological. This method is an essential step in authentication, but it must be supplemented by other scientific analyses. There are two dating methods used by CIRAM laboratories:

• Carbon-14 dating is used exclusively for organic materials: wood, paper, ivory, bone, leather, and textiles
• Thermoluminescence, used for terracotta and heated materials.

Which materials in a painting can be dated?

Not all materials used in a painting can be dated using carbon-14, as shown in the table below:

Why isn't carbon-14 dating sufficient to authenticate a painting?

Please note that the date on a work’s medium does not automatically correspond to the date the work was created.

When studying paintings, various imaging techniques—such as those using natural light, raking light, ultraviolet (UV) light, or infrared (IR) reflectography—complement conventional dating methods. However, one problem remains: how can we analyze materials that cannot be dated, such as the pigments used in paintings?

An anthropological and historical approach to complete the results

Historical knowledge of pigment manufacturing techniques will provide chronological data: the use of chromium oxide as a green pigment from 1840 onwards, for example, or the manufacture of titanium white (titanium oxide), which began in the 1920s. These investigations also have their limits: natural pigments provide no real chronological information, as in the case of ochre, which was used for the Lascaux cave paintings!

How is a painting dated?

Dating a painting begins with identifying the materials it is made of in order to determine which ones can be analyzed. A very small sample is then taken from an organic material, such as canvas, wood, or paper. After measuring the carbon-14 levels and calibrating the results, the data obtained are interpreted by comparing them with pigment analyses, scientific imaging, and historical knowledge.

The principles of carbon-14 dating

Carbon-14 dating measures the time that has elapsed since the death of a living organism. Just as death brings human life to an end, a plant’s life ends when it is harvested. For a painting, this corresponds to the time when the flax or hemp used to make the canvas was harvested or when the tree used for the support or frame was felled.

The principles of carbon-14 dating are based on the instability of the carbon-14 isotope. A living organism contains a constant amount of carbon-14 due to exchanges with the atmosphere (respiration or photosynthesis). When the organism dies, these exchanges with the outside world cease, and the amount of carbon-14 then decreases according to a known exponential rate. Its concentration is halved every 5,730 years. The dating limit is approximately 60,000 years. Beyond that, the amount of carbon-14 is too low to be measured by current techniques.

This revolutionary technique earned its inventor, Willard Frank Libby, the Nobel Prize for Chemistry in 1960.

Carbon-14 variation over time, an important factor to take into account

Carbon-14 dates are expressed in years “Before Present” or “BP.” The “present” for carbon-14 was set at 1950 by Libby. Today, however, these values must be corrected because the concentration of carbon-14 has varied over time due to factors such as solar activity, climate change, and industrial activity. These results are referred to as calibrated results, obtained using calibration curves. These curves allow the BP age to be converted into calibrated date ranges associated with a probability percentage (for example, 450 ± 25 years BP corresponds, after calibration, to the range 1422–1471 AD—with a 95.4% probability).

The onset of industrial activity, for its part, led to a decline in Carbon 14 levels and imposed limits on the precision of measurements. Conversely, atmospheric nuclear testing has led to an artificial rise in Carbon 14 levels worldwide. This makes it possible to obtain very precise dates (up to one or two years) for the second half of the 20th century.

Some examples of paintings dated and authenticated by carbon 14

The following examples illustrate how carbon-14 dating can reveal chronological inconsistencies, but also why it must always be cross-checked with other scientific analyses.

In art history, cases of forgery are common, and it is often through a thorough analysis that inconsistencies have been uncovered. Here are two examples:

• A painting by a Russian Suprematist painter, dated 1920, had its canvas support finally dated post 1954.
• A Picasso composition proposed for dating in the early 20th century revealed, after dating the paper support, that the paper had been manufactured before 1954, and was therefore incompatible with the presumed period.

Generally speaking, it's much easier to prove that a painting is fake than to establish its authenticity:

• The dating of a painting attributed to Van Gogh was carried out in two stages. Dating of the support suggested a date compatible with the painter's activity, at the end of the 19th century. Pigment analysis led to a similar conclusion, since the pigments detected were known in the 19th century and had been found in other works by Van Gogh. These included vermilion red, copper arsenate green, zinc white and ochre. However, these pigments were known and used by all painters at the same time, and even today. The Van Gogh committee, made up of art historians, had to decide in favor of an original work.
• Conversely, analysis of a 14th-century illuminated parchment confirmed the dating of the support. As for the pigments, they proved to be modern... It was an "intelligent" copy made before 1950... on old paper. It is therefore essential to combine analytical techniques to detect forgeries.

Carbon-14 dating is a key tool for the study and authentication of paintings, but it cannot, on its own, establish the authenticity of a work. Only a multidisciplinary approach—combining carbon-14 dating, chemical analysis of materials, scientific imaging, and art-historical expertise—can provide a reliable interpretation of the results.

Richard Cheret

Richard holds a master’s degree in chemistry (1999) and a master’s degree in the physics of archaeomaterials (2000) from the University of Bordeaux. In 2005, he co-founded the CIRAM laboratory with Olivier Bobin, and today serves as its co-manager and sales director.

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