D.2 TECHNIQUES FOR ANALYSING THE MATERIALS IN THE GALLERIES

Different instruments and analytical techniques can be used to identify the materials at the Punta Begoña Galleries. Many of these techniques are destructive, which means that a sample needs to be taken and then dissolved in order to conduct the analysis. In this case, however, we have tried to use non-destructive techniques whenever possible.

The non-destructive techniques used are X-ray fluorescence (XRF) and Raman spectroscopy. These two techniques have the added advantage of being able to take the readings in situ, at the galleries, without having to remove samples, using portable instruments for measuring the materials directly.

The techniques complement each other:

• The first technique tells us about the elements in the materials (e.g., sulphur and calcium) by measuring the x-rays emitted by the sample when they receive more powerful x-rays.
• The second one provides data on the molecules to be found (e.g., calcium sulphate – CaSO₄ formed by the aforementioned elements) depending on where the signals appear in the light dispersed when they are radiated with a laser.

Conducting a more detailed analysis requires taking samples and analysing them in a laboratory, using either destructive or non-destructive techniques, with other instruments (ionic chromatograph, ICP-MS, SEM-EDX, etc.) which provide us with data on elements or compounds that are to be found in smaller concentrations and which cannot be seen in situ. We used all these techniques to analyse the different materials; those materials found inside and on a uniform basis are the original ones, while those found on surfaces and on a more varied basis in crusts, cracks and stains are degraded materials.