The frequency of these periodic vibrational motion is known as vibration frequency and it’s characteristic of each chemical compound.
Therefore, if the vibrational frequencies of a molecule can be measured, it is possible to compare those to a database of frequencies and determine the name of the molecule. The most direct way to probe the vibrational frequencies of a molecule is through infrared spectroscopy.
Infrared spectroscopy measurements became routine, while Raman spectroscopy still required skilled operators and darkroom facilities, and needed to be constantly maintained and calibrated.
During the 1990s, the development of CCD as spectroscopy detectors and lasers led to cheaper and easy-to-use Raman spectrometers.
Therefore, the lead white mixed with red pigment for the illustration’s flesh tone has turned to black lead sulfide. By the end of the 1930s, Raman spectroscopy had become the principle method of non-destructive chemical analysis.
Infrared spectroscopy became the preferred method after World War II, primarily because it became much easier to use due to the development of sensitive infrared detectors and advances in electronics.
Raman spectra consist of sharp peaks whose position and height are characteristic of each specific molecule. Because of these differences, Raman spectroscopists compare their sample to Raman spectra databases of materials to discover the sample’s chemical composition.
Other pigments may be known to have disappeared from the artists’ palette, so their presence permits experts to date artifacts ante quem.
Spectroscopy may also help uncover the manufacturing methods used to fabricate artistic materials, providing valuable data about the development of technical skills over time.
Spectroscopy also enables scholars to date objects.
This is because vibrational transitions typically require an amount of energy that corresponds to the infrared region of the spectrum.
Raman spectroscopy, which typically uses visible light, can also be used to directly measure vibration frequencies.