- A team of researchers from SASTRA University, Thanjavur, Tamil Nadu have found a solution that uses Raman spectroscopy to tell whether the foil used in the Tanjavur paintings is made of gold or some other cheaper material.
- Thanjavur paintings have Geographical Indication tags, which puts a premium on their authenticity.
- However there are no regulations governing the quality or authenticity of the paintings.It is a well known fact that not every Thanjavur painting that glitters is gold.
- There was, however, no way to find out if the gold foil and gemstones used in these traditional crafts were authentic or fake.
- Foils made of fake material look similar to genuine gold, making it difficult for consumers to tell the difference.
- In a study recently the researchers tested ten ‘gold foils’ and found only three to be genuine.
- In the case of paintings, only one or two out of ten turned out to be genuine gold foil.
- Therefore the researchers suggested framing of regulations for Thanjavur paintings.
- Raman spectroscopy, which helps identify molecules in ‘gold’ foil was the method used in the study.
- The researchers also validated their detection of fake gold by carrying out an energy dispersive X-ray analysis (EDX) of the paintings.
- The gold foils and paintings used in the study were sourced from artisans from in and around Thanjavur.
Why gold foil is used?
The gold foil used liberally in Thanjavur paintings serves two objectives:
- The glitter makes the painting more attractive
- It also prolongs the life of the artefact
Principle behind spectroscopy
- Spectroscopy is the systematic study of spectra and spectral lines.
- Reflection, refraction and absorption are all a category of scattering depending on whether the photon is reflected, refracted or absorbed by the material on which it is incident.
- The amount of reflection, refraction and absorbtion gives a characteristic pattern on the spectra as emission, continuous and absorption lines as shown in the figure.
- Each chemical element produces its own unique characteristic pattern of spectral lines.
- The specific wavelengths observed depend on the chemical composition of the material.
Rayleigh scattering and Raman scattering
- Rayleigh scattering refers to the scattering of light off of the molecules of the air.
- The energy of incident light is same as the energy of scattered light.
- Scattering in which the scattered photons have either a higher or lower photon energy than the incident photon is called Raman scattering.
- Raman spectroscopy is one of the vibrational spectroscopic techniques used to provide information on molecular vibrations and crystal structures.
- This technique uses a laser light source to irradiate a sample, and generates an infinitesimal amount of Raman scattered light, which is detected as a Raman spectrum using a CCD camera.
Advantages of Raman spectroscopy
- Raman spectroscopy does not require the removal of the frame and the glass as it is non-destructive.
About Tanjavur Paintings
- Tanjore Painting of India originated during the 16th century, under the reign of the Cholas.
- Maratha princes, Nayakas, Rajus communities of Tanjore and Trichi and Naidus of Madurai also patronized Indian Thanjavur Paintings from 16th to 18th century.
- The dense composition, surface richness, vibrant colors, embellishments of semi-precious stones, pearls and glass pieces are the characteristic features of Tanjavur paintings.
- The relief work gives them a three dimensional effect.
- Most of these paintings revolve around the theme of Hindu Gods and Goddesses, along with saints.
- Since Tanjore paintings are mainly done on solid wood planks, they are locally known as ‘Palagai Padam’ (palagai meaning wooden plank and padam meaning picture).
Making of Tanjavur paintings
- The base is made up of a cloth, which is pasted over a wooden base.
- The second step consists of mixing chalk powder or zinc oxide with water-soluble adhesive and applying it on the base. T
- hereafter, the drawing is made and ornamented with cut glass, pearls and even semi-precious stones.
- Laces or threads may also be used to decorate the painting.
- To further augment the effect, wafer thin sheets of gold are pasted in relief on some parts of the painting.