Teaching science and humanities: an interdisciplinary approach
Submitted by sis on 04 August 2006
An interdisciplinary approach
In terms of mathematics, perspective and the golden ratio are undoubtedly the most important topics to address, but students could also set themselves a geometric goal: to calculate the volume and the area of the vault, for example.
Students addressed the earth sciences by identifying the stone illustrated on the walls, by comparing it to samples of marble, jasper, porphyry and other materials on display in their local museum. Other possibilities in the earth and natural sciences would be to investigate the gems worn by some characters, or to identify the clams and coral and to study their natural environment and life cycle. The most appropriate discussions would depend on the type of museum available.
The chemist's imagination is bound to be captured by colours, and so we decided to prepare one of the pigments that was used by the painter. What kind of pigments did he use? When a painter or a painting is as famous as Piero della Francesca and his works, you can find a lot of information on the worldwide web. Further assistance was available from the Monuments and Fine Arts Office for Pisa, Lucca and Massa Carrara. We looked through entries and reports, and discovered that the linen cloth on the nine wooden boards which support the painting was dyed with alizarin lake. Alizarin is obtained from the roots of madder, Rubia tinctorum, a common European plant. And so we departed for the woods and hills, looking for madder roots...
From madder to alizarin
Madder, common across Europe, is a crawling plant up to 1.5 metres long. The flower is white-yellow and the fruit is a pink-red berry. The stem bears clusters of five or six leaves, the lower sides of which are sticky and rough. The roots are reddish.
Alizarin exists mainly in the fleshy roots in the form of its glycoside, ruberythric acid. Pieces of rinsed roots are treated with a hydrochloric acid solution to hydrolyse the ruberythric acid and remove flavonoids, which would otherwise dull the pigment. The roots are then dried and treated with a solution of alum to extract the alizarin, which forms a red complex.
To obtain the pigment, a soda solution is added to precipitate aluminium hydroxide, which adsorbs alizarin. The pigment, once strained, rinsed and dried, can be used for tempera and oil painting.
The alizarin content of the roots depends on the season and on the kind of soil, although the average content is about 1.9% w/w.
The search for hidden images in paintings
If a painting is illuminated by white light, blue-ultraviolet images include information mainly on surface features, whereas images captured at longer wavelengths carry information on deeper layers of the painting. Therefore, by taking images using different wavelengths, we hoped to discover pentimentos: hidden traces of earlier painting.
The chemical composition of a painting begins to change the moment the painter finishes working on it, because substances undergo oxidative and degradative processes, so pigment colours may change or fade with time. Further changes in composition may be due to restorations. When a mercury lamp filtered to transmit 365 nanometres is used as the excitation light source, part of the ultraviolet radiation is absorbed and given off with a lower energy in the visible region of the spectrum: as fluorescence. With this apparatus, we were able to look for restorations made with pigments that differed from those originally used by Pietro da Talada.
I have seldom seen my students working with such enthusiasm as when, burning with curiosity, they searched for pentimentos. One fine day, the much-anticipated discovery was made! While analysing the painting kept at the Lucca Savings Bank Foundation, we found a pentimento: Pietro da Talada appeared to have changed his mind about the position of a fold of cloth (see above). We were in seventh heaven!
The same day, using fluorescence, we discovered a restoration, highlighted by different shades of pink (see above).
It was a very snowy and cold day, but when I realized that my students were fully aware of how much beauty there is in science, and how much science in beauty, it warmed my heart.
This article is an interesting indication of the links between the humanities and the sciences, showing different ways of approaching the topics of electromagnetic waves and dyes.
The protocol for extracting dye is straightforward enough to be carried out in schools and also provides a link to history and botany - as well as an excuse to take a chemistry class outside to search for plants.
The physics-based section describes an interesting way to introduce the idea of the electromagnetic spectrum but is probably more difficult to reproduce in most secondary schools, as it requires specialist equipment. It does, however, provide an interesting link to forensic science and how art forgeries can be identified.
The main difficulty with reproducing the science in this article in many schools would be in obtaining access to the specialist lighting and spectral analysis equipment as well as specific works of art. The article can, however, be used as a source of information or as a topic of discussion.
Gianluca Farusi teaches chemistry at the technical school (istituto tecnico industriale) Galileo Galilei in Carrara, Italy. He is also teaches stoichiometry at the University of Pisa, Italy.