Art Forensics #8:

Forensic Science and Fine Art Media Testing

Read previous articles in the Art Forensics Series

Introduction

Fine art is created using many different media. There are close to 50 categories of fine art media including stone, paint, wood, paper, crayon, ink, plastic, fabric, steel, and so on. One merely has to visit a local museum to observe the many different ways artists have taken the materials from the environment to create their art. The list of categories is growing and perhaps never ending since new materials are constantly being developed via the march of technology and artistic creativity. Herb Williams, a Tennessee artist, uses crayons as sculpture; Jenn Greenleaf cuts up strips of newspapers heated and turned into a mush for her sculptures; and Barbara Wiesen uses blood in her art. Further, evolutionary art takes the process of evolution to create an artwork which changes via an evolutionary algorithm. As artists play with these materials, new uses of old non-art materials develop. Reinforced concrete normally used for building construction has blossomed as a medium for sculpture, furniture, and even jewelry. Each medium consists of chemicals which have a timeline of origination or identification. Paint pigments such lazurite, vermilion, calcite, lead white, and red and yellow iron oxides were used by 17th century Dutch artists. Linking the paint pigments or media in a work by comparing them to other known works of given artists allows the forensic examiner to assert scientific evidence of an attribution between work and artist.

This is not to say that the media alone provide complete evidence, but in conjunction with other sources of evidence such as provenance documents and connoisseurial notes, add to the probability of authenticity and attribution. The Museo d'Arte e Scienza (Museum of Art and Science located in Milan, Italy) argues that because provenance and stylistic/connoisseurial evidence can be easily copied, the most significant determinant of authenticity is scientific evidence. The museum notes that the more subjectivity in authentication, the better for those who sell works.

Forensic Testing Approaches

Testing approaches of fine art works move from simple to the more complex. The most simple approaches are to use a magnifying glass to examine a work for craquelure, paint pigment size, and surface appearances. Craquelure or paint cracking usually occurs after 60-120 years. It starts near the wood under the canvas, and is more prevalent in white paints. Large paint pigments are indicative of older paints ground by the painter as opposed to small size pigments developed by industry. Bright yellow pigments do not maintain their brightness through time and tend to turn dull or greenish brown. Surfaces on antique paintings were usually protected with varnishes. Cleaning varnishes should produce a grey paint surface underneath. Cleaning should be done near the borders of the work.

Moving toward greater levels of testing, an owner may take a sample of the work and bring it to a lab for examination. Here the owner of a work takes minute samples of the back of the painting's panel, or stretcher of the canvas, paints, and canvas matter and brings them to the lab. This destructive sampling must be carried out with the greatest of diligence so as not to create issues for the work. Large holes in the canvas will not do much to improve the value of the piece even if it is found to be authentic as a result of making them.

The most complex and costly examination is providing a lab with the actual work and allowing them to conduct a thorough examination. The results of the examination will provide a clear picture of the age of the work in most cases. Works created after 1920 do not have as many scientific standards for evaluation. Carbon dating is not accurate for more up-to-date works.

Forensic Scientific Testing Processes

There are four main tests used to determine the age of a painting:

• infrared reflectography
• Wood's light
• a stereoscopic microscope
• IR spectroscopy.

Infrared reflectography focuses on the layers of painting and the sketch made by the use of carbon black or charcoal by the artist. The different layers or alterations of the work are known as pentimenti. The alterations tell us the extent of restoration, whether or not it is a copy, and the different materials used. The more pentimenti the more it is likely that the work is the prime version.

Wood's Light seeks to identify the different types of fluorescent matter in a work. Fluorescent matter emits radiation and the quantitative levels emitted link the work to a given time.

Infrared spectroscopy (IR spectroscopy) is the subset of spectroscopy that deals with the infrared region of the electromagnetic spectrum. It is a method of identifying substances making up a work and tying them to a given period.

Microscopic analysis allows the viewer to see beneath the surface and identify the particles within the structure of the work. Particles or minute matter comprising the work have birth and death times: materials are created at a particular point in time, and die out from disuse, exhaustion (supply no longer available), or regulations outlawing their use. The pigment Verona Green was exhausted in 1930, yellow iron oxide (mars yellow) was created in the lab some time in the 1920s, and the use of lead in paint was outlawed for the most part in the 1980s due to negative health consequences. The type of pigment used in a work tells us in what time frame the work was created or restored.

Processes not normally used are dendrochronology and carbon dating. Dendrochronology is used to date a wooden object by counting the number of tree rings present in the object. This is of limited use, though, as before the piece can be accurately dated by this method, the wood needs to have about 100 rings. Carbon-14 dating examines fine art materials for the presence of radioisotopes. Their quantitative levels present determine the age of the material. Similar to dendrochronology, carbon-14 is less accurate for contemporary objects than antique ones.

Please note here that there are many more methods available to test materials in a work of art. One could argue that the more tests, the more data available to support a conclusion. The choice of the number of tests is a function of the number of unanswered questions surrounding the analysis. Using the ones noted provides an acceptable level of probability of establishing authentic v. inauthentic. If we failed to ascertain the age of the wood in the stretcher or panel via dendrochronology, any conclusions regarding authenticity could easily be taken to task. If the panel wood is not corroborated with the paint pigment one would ask how the old world paint could be applied to newly developed materials.

Case Study of Forensics Science

Through microscopic analysis, the canvas size, weaving and manner of attachment was found to be standard for the period and the type Constable used for his works. Additionally the preparatory layer for the paint and stretcher configuration is similar to Constable’s other authenticated works. Paint pigment analysis identified the use of vermillion of the type used in the 1820s-1830s, and typical for Constable's works. Ultraviolet fluorescence noted that the varnish Dammar was used and its first documented use was 1839, inferring that it was used earlier. Fluorescence did not find any significant overpainted areas showing that the work was intact, and Infrared reflectography indicated that some areas were changed and replaced with other images, and that for the most part very little underdrawing took place. The conclusions are that the painting was created in the first half of the 19th century with a minimal amount of restoration or repair, and similar technically to other works of Constable (actual case study and conclusions, http://www.conservartassoc.com/spie.html).

It is important to note here that scientific analysis is one of the three towers of fine art authentication - science, provenance, and connoisseurship. Science does not authenticate. It establishes what is not authentic. If the canvas, paint, or stretchers were produced in 2008, scientific analysis would argue that the painting was not by Constable since the materials/media were not around when Constable painted. You can't produce works if the media is not available. Science provides conclusions regarding the age and technology of the materials used.

Summary

Scientific analysis of works of art focus on the materials used to produce the work. Science has been able to establish time periods for materials used in terms of origination and death of a given material. Works produced at a given time must match the materials and technology existing during the period. Mismatches indicate inauthenticity. A work allegedly created in 1850 whose paint pigments were not available until 1930 would not be considered authentic because you can't create 1850 works using 1930 materials. Scientific analysis should be the first step in the analysis of authentication because if analysis concludes that the materials do not support the time of creation any other non-scientific conclusions have no value – it is the quickest way to establish inauthenticity in a work of art, thus obviating the need for other more time-consuming and expensive approaches.

Conclusions

Forensic science and fine art authentication involves the testing of the various components of a work of art for age and technology. Some points to consider:

1. Testing of materials should be the first step in the fine art authentication process.
2. If testing disproves authenticity no other non-scientific examinations may establish authenticity.
3. Testing approaches move from the simple to the complex as a function of cost and required outcome.
4. Care must be taken in performing destructive testing. Such testing should only be performed by a laboratory experienced in fine art examination.
5. Insurance should be considered in destructive testing.
6. Authenticity determinations must be developed from not only testing but provenance research and connoisseurship.
7. Note that there are many more testing processes in addition to the processes covered here.
8. Some testing processes are more accurate for aged objects than contemporary ones.

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— by John Daab Ph.D.  |  January 27, 2010

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