Art Experts, Inc.: Analyzing pigments in paintings

Many of those who own valuable paintings that need to be authenticated often labor under the illusion that expensive scientific techniques can answer all the questions they may have about their painting. This, unfortunately, is not the case. Although, there is no doubt that the collaboration of art, and science is sometimes imperative to authenticate or date a painting, this is just part of the jigsaw puzzle. The results of scientific techniques alone will not give you all the answers you need in relation to your painting.

The History of Pigment in Art
The biggest element that researchers look for in pigment analysis is the specific type of pigment. This will tell researchers and authenticators everything from what type of pigment the artist used, to whether or not a certain pigment was even in existence at the time the painting was created.

The following is a timeline of popular pigments that were used in the creation of paint throughout the years. Some from the prehistoric era are still used today!

Prehistoric/Ancient Pigments
Ochre: Often used for glazes, ochre can either be opaque or transparent. Used throughout history and today. Made from naturally tinted clay. This is perhaps one of the most commonly found pigments families in the history of color, and are still used today.

Contemporary Pigments

It has been our experience here at Art Experts that people will often pay expensive fees to have Pigment Analysis carried out on a painting, only to be disappointed when the results do not answer all their questions on the painting. Often this disappointment stems from the fact that they don't realize scientific techniques such as Pigment Analysis have limitations. The results of this technique are normally of no use whatsoever, unless they are used in conjunction with the expertise of an art expert.

*This x-ray of "Fete Champetre" by Jean Antoine Watteau can uncover metals and pigments used in the painting. But, can it really tell you if it was indeed painted by Watteau?

In all honesty, Pigment Analysis by itself can sometimes confirm a negative. All that Pigment Analysis does is confirm that a painting is not by a particular artist. Pigment Analysis alone will almost never help you determine if it is by a particular artist. Yet, when someone decides to authenticate a painting, they often do so because they want confirmation of a positive statement. If they have a painting that is signed by Degas, they want to pay money for a service that is just as capable of confirming that it is a Degas, as it is of telling them that it is not.

*Upon pigment analysis of this pastel composition, a researcher may find that Degas used emerald green pigment, created from a poisonous copper. But how many other artists used this same kind of pigment? Only research can truly determine whether a pastel of this kind was truly created by Degas.

In order to illustrate this point, let's take the example of someone who thinks they own a painting by Vermeer and would like it authenticated. Pigment Analysis may be able to tell them that it is not a Vermeer, as the results may show pigments which were not in use in his time. However, if the result is that the pigments found were in use, this in itself is not enough to confirm that the artist was Vermeer. This does not mean that it was not something painted during Vermeer's time. It could very well have been, but what the owner wants to know is whether it is by Vermeer. This the question he wants answered. In order to to get the answer, the owner of the painting will need the help of an expert. This person who is an expert in signatures, the style of paintings by various artists, as well as being well qualified to spot forgeries, will be able to answser the question with the help of Pigment Analysis. Therefore, in order to get an accurate identification of a painting by a particular artist, Pigment Analysis is only useful when combined with the expertise of a qualified art expert.

*Vermeer would often use lead white pigment in his paintings, as he certainly did for "The Art of Painting." Vermeer would also use yellow ocher, azurite and smalt. But how many other Vermeer forgers use these same pigments at the same time? This is why research is also pertinent.

*There is some controversy over Da Vinci's "Adoration of the Magi" concerning the brown and yellow ochre used to color in this unfinished piece. Some authenticators have argued that it was not Da Vinci that added the brown and yellow coloring, but another artist. However, this is not argued just because of the coloring, but also because of the method that the artist used to apply the paint.

We have spoken a lot about Pigment Analysis, but what exactly is it? Well, it is a technique that is used to identify the raw materials and pigments used in a painting. A pigment is simply any material which results in color. Pigment is the result of selective absorption, therefore there is no such thing as white pigment. Pigments work by selectively absorbing some parts of the visible spectrum. Pigment, usually an insoluble powder, is what gives paint its color. Of course, different pigments have been used throughout art history. Some of these same pigments were used during pre-historic times, but in a more primitive form. Prehistoric man mixed dirt and clay with saliva to make paint. For example, Charcoal Black and other pigments were used in the famous cave paintings in the caves at Lascaux, France. In the famous cave paintings at the Lascaux Caves in France, charcoal black and other pigments was used.

Prehistoric man also used iron oxide pigments to obtain the deep red colors that he often used. Iron Oxide and other minerals continued to be used in the Renaissance, and such painters as Michelangelo used the natural red chalk dug from the earth to create their masterpieces. Renaissance painters often used terra verte (or "green earth") to create the under painting shadow for flesh tones. Of course as time went by, man began to use pigments manufactured in laboratories, and today there are very sophisticated chemically manufactured pigments available.

As a result of the fact that different pigments were used throughout periods of art history, the identification of the pigments in a painting by Pigment Analysis can give art experts clues as to the period when the painting was executed. The result of the Pigment Analysis can also help the art expert to conclude that the painting was not by a particular artist. If the expert is brought a painting which the owner purports to be by an artist from the sixteenth century, and the pigment analysis shows materials which were manufactured in laboratories only from the nineteenth century onwards, then clearly this is not a painting from an artist from the sixteenth century. Likewise, if the expert is brought a painting of which the owner does not know the date, and the pigment analysis shows terra verte, then the expert will use this as evidence to deduce that the painting is by a Renaissance painter. However, in both cases, neither the most sophisticated Pigment Analysis procedure nor machine could identify the artist of the painting. For this, the human skills of the art expert are required.

I hope now that readers will understand that Pigment Analysis is essentially a technique used to identify pigments and raw materials used in a painting. But, how exactly does it work? Pigment analysis falls into two categories, invasive and non-invasive analysis.

The non-invasive techniques normally involve the use of spectroscopy. When we talk about spectroscopy, we mean the study of spectra, which is basically light. The study of spectra is the dependence of physical quantities on frequency. Spectroscopy, therefore, is the study of light on matter, and it is thus useful for identifying substances and materials. Spectroscopy is often used in physical and analytical chemistry. It is also frequently used in astronomy.

The two non-invasive techniques of Pigment Analysis using spectroscopy are called X-Ray Fluorescence Spectroscopy and Raman Spectroscopy. X-Ray Fluorescence Spectroscopy (often known as XRFS) is based on elemental analysis, and can be used to identify most elements with an atomic number equal or greater to aluminum. It can, therefore, not only identify pigments and materials in paintings, but can also, for example, identify the major and minor elements in bronze works of art.

Raman Spectroscopy is based on the analysis of molecular structural motives. There are some pigments that Raman Spectroscopy is not able to identify due to the fluorescence of binding materials. When this is the case, XFRS may also be used to provide complimentary results. Both of these techniques are applicable and are non-invasive, as neither requires the taking of a sample of the painting.

In contrast, Gas Chromatography is classed as an invasive technique which requires a small sample of the painting. This technique was used, for example, to identify the wall paintings of the Mogoa Grottoes in China, which is a world heritage site on the Silk Road.

Gas Chromatography is used to identify organic substances and is widely used by the pharmaceutical industry. In the world of art it is used to identify the artist's media, such as oils, resins and waxes. In Gas Chromatography, a vaporized sample is introduced and carried along through a thin column by an inert carrier gas, where the sample components are separated. The components are then flushed sequentially from the column through a detector. The end of the column can be coupled directly to the mass spectrometer. The mass spectrometer breaks up the constituents into molecule ions which then pass through a magnetic field that separates them and allows the materials to be identified.

This article could go on for many more pages explaining the complicated physics and science behind the different techniques of Pigment Analysis. At the end of the day, the most important thing to understand is that they are only techniques for identifying pigments and materials. They can not tell you who the artist of a painting is. Paintings can often be authenticated solely using the skills of a well qualified art expert without recourse to expensive scientific techniques.

Here at Art Experts it is often a case of collaboration between art experts world wide. We aim to give the best service possible, and if the skills of an expert in France are needed, we do not hesitate to call upon them. We do not dismiss the role of Pigment Analysis when it is needed, and we have enough experience to be able to identify this need according to the piece of art involved. When it is needed we work in collaboration with one of the best laboratories in the field.

If you need to authenticate your painting, before you write out a large check for Pigment Analysis, please call us, and we can advice whether it really is necessary.