Portable XRF Technology for Archaeometry and Authentication and Conservation of Art Objects

Overview

Art objects have been studied with X-rays virtually from the inception of this technology.

When Wilhelm Roentgen discovered X-rays in 1895, one of his first experiments was a film of his wife Bertha's left hand, clearly revealing the ring on her finger.

Of course, X-ray technology has evolved tremendously since those early experiments. Today it allows extensive qualitative and quantitative analysis of historically significant objects. However, much of these analyses have been limited to laboratory work, where the object must be transported to a lab, and frequently altered or even destroyed, in order to analyze it. Now, portable XRF systems permit field scientists to analyze objects immediately without transporting, altering, or damaging them.

For decades field portable XRF systems have been providing rapid, on-site measurements of metals in soil for environmental studies - and of alloys for industrial applications. Only recently have they been used as in-situ, non-destructive analytical tools for conservation and archaeometry.

The DELTA can be configured with an optional camera/collimator to inspect very small areas on valuable objects.

Archaeometallurgy

Archaeometallurgy is concerned with the analysis of metallic objects of cultural value. Investigations are on pieces as small as jewelry or as large as seagoing vessels, such as the H.L. Hunley - the first attack submarine ever constructed.

Built in 1863 by the Confederacy, the Hunley attacked and sank the USS Housatonic outside of Charleston Harbor (SC). The sub never returned from her maiden combat voyage, and is sometimes referred to as the "iron tomb." It was located and raised off the coast of Charleston in August of 2000. Hunley preservation and conservation efforts continue today. A critical requirement of this preservation task is to identify accurately the metallurgy of the various components of the sub. The portable XRF analyzer was chosen for this because of its state-of-the-art software, versatile X-ray analysis with multiple filter options - plus the ability to add new elements, new alloy grades and fine-tune calibrations specific to the job. Handheld XRF provides the performance, portability and versatility required for the unique challenges of cultural heritage objects.

Bronze Age: Copper Based Alloy Analysis

XRF analysis not only offers clues about metals in the relatively late Iron Age, such as for the Hunley, it also answers questions about metals in the Bronze Age - a much earlier time.

Some bronze objects are simply two component copper based alloys. More often there are several components. The identity and/or concentration of these help to determine the composition, provenance, technology and authenticity of an object.

Commonly produced copper based alloys found from the Bronze Age, including gunmetal and leaded gunmetal, consist of 1-15% Sn/Pb, up to 28% Zn, and Cu making up the balance. Trace levels of other elements, such as Sb, can indicate impurities in the ores and can give information about the object's origin.

The presence of Zn at levels higher than 28% or the absence of other trace elements can indicate that the piece is from a time period after the Bronze Age. Copper based alloys are very simple to analyze with XRF. Detection limits in alloys range from 0.1 to 0.5% depending on the element and the sample matrix. An XRF spectral overlay of two different bronze alloys can be seen in Figure 1.

Paintings and Art Objects: XRF Analysis for Authentication and Conservation

As we all know, everything isn't always what it seems or what someone says it is. When there is any doubt about the authenticity of a painting or other art object, an investigation is required. XRF can give information necessary to determine the authenticity of a painting by analyzing its pigment or, in the case of ceramics and statues, the base materials as well.

Essentially, different pigments have been used at different times in history, at different locations and by different artists. In other words, the materials used to make pigments can vary considerably by artist, region and date.

XRF analysis of the pigments can answer the questions of when, where and by whom the pigments were made. If this information does not concur with what is known about the attributed artist's pigment materials, then forgeries can be revealed. The same is true about the base materials of ceramics and statues. Information gained from authentication studies is also used to help repair and restore an object by allowing the conservator to produce materials similar to that of the original art object.

For example, the painting shown here is believed to be a 16th Century Venetian portrait of Mary Magdalene. XRF analysis of the pigments used can help to determine its authenticity. The content of the red wax seals on the four corners of the back of the painting can also be analyzed by XRF to learn about its provenance, or ownership trail.