THE NMR-MOUSE and Applications of the NMR-MOUSE in Cultural Heritage

A MOUSE??! No, this is not a real living mouse that runs freely around cultural heritage sites, if that’s what you have in mind. Nor is it a computer mouse to facilitate interaction between humans and computers. So what is it then?

The NMR-MOUSE stands for Nuclear Magnetic Resonance - MObile Universal Surface Explorer. I know this sounds like a tongue twister, but the simple way to view it is as a mobile NMR magnet. If you want to know what this means, keep on reading. The NMR-MOUSE was initially developed in the group of Prof. Bernhard Bluemich at RWTH-Aachen University, currently being manufactured by Magritek, and it has many applications, including its use in the field of cultural heritage.

The science of the NMR-MOUSE

The NMR-MOUSE is a mobile NMR sensor that records NMR experiments in low magnetic fields. These magnetic fields are a few times smaller than the magnetic fields of the MRI magnets used in hospitals. Unlike the MRI magnets, which use superconducting magnets, the NMR-MOUSE uses permanent magnets (the black box in the picture) to create the magnetic field. A surface coil is then attached to the magnet. This coil sends radio-frequency pulses into an area of the sample which we want to investigate. The nuclei of the sample respond differently to these radio-frequency pulses depending on their environment. For example, if you’re comparing the response of a porous sample, such as a building wall situated in a humid environment and one from a dry environment, you will get very different NMR results. That is because the wall in the humid environment absorbs water and this leads to changes in the NMR signal. These signals are detected by the same coil that sent the radio-frequency pulses to the sample and we analyze them to extract different information about the sample.

The NMR-MOUSE is placed on a sliding table to move the sensor up and down, or left and right, with respect to the sample. This allows us to record NMR experiments at different depths in the sample and obtain a stratigraphy of the sample we measure. For example, we can see the different layers of a painting, monitor the water penetration into a wall painting and distinguish between the different anatomical structures of the bone.

Advantages of using the NMR-MOUSE in cultural heritage

There are two major advantages of using the NMR-MOUSE in cultural heritage:

• They are portable instruments. This means that the experiments can be recorded on site at the location of the analyzed object. Therefore, we can do NMR experiments inside museums, in archaeological sites, or in any other location, such as morgues or police stations. You’re probably wondering what do the last two locations have to do with cultural heritage. In my research I’ve done experiments in both: in the morgue measuring a mummified human cadaver for a project on ancient mummies and bones, and in the police station measuring painting forgeries to develop a method that uses the NMR-MOUSE to authenticate paintings.

• They are non-invasive tools. This is very important when working in cultural heritage because we want to make sure we don’t damage the sample during the experiments. When you work in cultural heritage, you want to protect the objects from any potential damage.

Applications of the NMR-MOUSE in cultural heritage

Being a mobile instrument that can record NMR experiments non-destructively makes the NMR-MOUSE an excellent tool for analyzing precious objects of cultural heritage. Here are some examples of objects and the type of information we can obtain using the NMR-MOUSE:

• PAINTINGS – information on the types of paints and treatments used in paintings, stratigraphy and authenticity of paintings

• HISTORICAL BUILDINGS AND FRESCOES – monitoring moisture content in wall paintings and analyzing their stratigraphy

• ANCIENT MUMMIES AND BONES – information on the state of conservation of mummies and bones

• HISTORICAL PAPER – characterizing the degradation of historical paper

• MUSICAL INSTRUMENTS – information about the wood structure and treatments of master violins