Art Forgeries

Article taken from Issue 3 of the Forensic Access Newsletter "Benchmark"

Dr Owen Facey, forensic chemist, explains how, with modern scientific techniques, they are difficult to miss.

At one time or another most art objects have been copied. Often, this has been for the legitimate purpose of training the next generation of artists. At other times, it has been because a copy was required, occasionally with the intent to deceive. Scientific techniques can be used to differentiate originals from later copies. While this fact has long been known, it has only recently become realistic to use scientific testing options through the availability of non-destructive and microanalytical techniques. With these techniques, it is possible to analyse the composition of the materials from which the art object is made and, knowing how the use of art materials has evolved over time, to separate the original from its later copy.

An example would be the artists’ colour chrome yellow. This fell out of favour in the mid-nineteenth century as the sulphurous fumes from industrial pollution slowly turned it black. It is, however, in use again, as modern chrome-yellow particles are coated to keep out the pollution. This coating can be observed using a scanning electron microscope (SEM). The presence of the coating shows that the painting was made within the last 30 years. It is small details like this, which are not well publicised, that make it so difficult to reproduce exactly the materials of past years, even when they appear, ostensibly, to be the same.

This is equally true of metal objects. Sterling silver has been available for hundreds of years, but the only requirement is that it must contain a minimum of 92.5% silver. The remaining 7.5% of other metals is more or less uncontrolled and has varied over the years. In recent times, small quantities of specific metals have been added to improve sterling silver’s workability and machining properties. In much the same way, most other modern metals differ in detail from their earlier counterparts. An SEM, with an analytical attachment, can determine the make-up of a metal, with the added advantage that, if the object is small enough, it can go directly into the SEM sample chamber – the analysis then becomes non-destructive.

It is always necessary to undertake a careful scientific evaluation before deciding on what and how testing should be carried out. For example, a genuine old painting will almost certainly have some restoration work present. Clearly, the test needs to be performed on what is thought to be original material. Each object presents its own challenge, but a careful scientific examination can help to determine whether or not it is genuine. In reality, it would not only be difficult to reproduce an art object so that it corresponds to a specific time, the attempt to do so would also probably cost more than the item was worth.