IR spectroscopy has been used for decades in laboratories and industry for chemical analyses. Recently it has started being applied for the dating of art objects in wood like furniture, painted panels, statues, musical instruments and also for African and Buddhist art. The measurement is based on the chemical alterations undergone by wood in the course of decades and centuries. The method is briefly described below.
All the molecules of which wood is composed vibrate at a fixed, but well distinguished frequency. If they are struck by IR radiations of the same frequency, they absorb the radiant energy. This absorption is represented by a curve.
Therefore, if an almost transparent tablet containing wood dust from a newly felled tree is inserted in a spectrometer, the computer records the absorption on the part of all the molecules of this particular type of wood and a curve corresponding to its chemical composition appears on the screen.
This curve is like a "fingerprint" taken of a type of wood and provides easily interpretable evidence without the need for complicated chemical analyses.
With the passing of centuries, the outer layer of an object made of this wood decomposes relatively quickly owing to environmental conditions, whilst the inside of the wood is subject to slow and almost constant chemical processes and above all the effect of micro-organisms.
This decomposition of the fresh wood and the formation of new molecular combinations transform the original curve pattern continuously and independently of outside influences.
Absolute dating can be achieved by comparing the pattern under examination to "archives" of patterns relating to samples of certain dating. The use of old wood for fakes can be detected by comparing the spectrum of the outer layer to the spectrum of the underlying wood. Only the heat- and humidity-resistant molecules are considered.
The worldwide application of spectroscopic analysis reduces the cost of equipment and procedures, making dating worthwhile even in the case of objects of lesser value.
 

There is a very full international bibliography available on the spectroscopic dating method.

1. Only spectroscopic analysis can detect the use of old wood for the fashioning of recent fakes.
2. Only spectroscopic measurements give unambiguous results. What is measured is the decay of the wood after the felling of the tree, and this decay is identical in the whole breadth of the trunk. Other methods measure the age of a specific and often unknown point of the trunk. If we bear in mind that trees were once allowed to grow for 300 years and more, it is obvious that this compromises the accuracy of results.
3. Measurements are not affected by the climate of the place of growth.
4. Spectroscopic analysis recognizes the most commonly used varieties of woods, the identification of which is important for the valuation of sculptures and furniture.
5. The dating method covers the entire period in which most antiques on the market originated.

• The modern instruments of the scientific laboratory and computerized data processing guarantee simple, fast, and inexpensive scientific analyses
• Practical demonstrations of the method at the Museo d'Arte e Scienza, Milan
• Ample descriptions in The Art Collector's Illustrated Handbook (Three volumes, over 2,000 detailed colour photos, concise explanatory texts)