In the previous experiment, you were introduced to Raman spectroscopy. This week you will explore how Raman spectroscopy can be used to solve real-world problems. You will use Raman spectroscopy to determine the validity of two paintings – one painting is a forgery and one is genuine. This analysis will allow you to gain experience in Raman spectroscopy and apply these principles to a real-world problem. You will have to make decisions to optimize the spectra and explain the reasoning behind these decisions. You will create a library of Raman spectra from known materials and use it to identify the presence or absence of those materials in other samples.
Art and Spectroscopy
Paintings often have a provenance – a record of the history and ownership of a painting. This provenance is often critical to authenticating a painting. If a painting does not have a provenance then it can be difficult or impossible to determine the authenticity of the painting – at least before modern scientific methods. Museums often turn to scientific tests to determine the composition of the paints used in the artwork. This provides evidence for when a painting a may have been created and who may have created it. Paints The type and composition of paints used in artwork has changed over time. Paints used before the 20th century often contain metal compounds, as most of the colored pigments available at the time were metal salts. Synthetic organic compounds became widely available in the 20th century and eventually replaced many of the metal salt pigments. Some pigments that were historically favored are no longer used due to their toxicity (e.g. lead, arsenic, and mercury containing pigments) and cost of metal saults (e.g. cobalt, cadmium, and chromium containing pigments). The paint color timeline below shows some common pigments and the timeline for their usage.
Mixtures in artwork
Paintings are seldom comprised of only type of paint or clearly delimited paint types. Most paintings
are composed of a mixture of paints to achieve the widest range of colors. Additionally, black and
white paints are often used to adjust the color and brightness of other pigments. How will you account
for paint mixtures when determining the authenticity of the paintings in this experiment?
Paint Color Timeline
Phthalocyanine Green Used since 1938
Viridian Used since 1859
Phthalocyanine Blue Used since 1938
Ultramarine (synthetic) Used since 1928
Cobalt Blue Used since 1804
Dioxazine Purple Used since 1952
Cobalt Violet Used since 1859
Cadmium Yellow Light Used since 1851
King’s Yellow Used since 1816
Mars Black Used since the early 20th century
Ivory Black Used since prehistory
Titanium White Used since 1921
Lead White Used since antiquity