Before (above) and after (below) the colour samples were taken from the terrestrial globe (left) and celestial globe (right), Ill. HKB|HEAB report.

• 785nm Raman spectroscopy for the pigments,
• FTIR (Infrared) spectroscopy for the binders,
• scanning electron microscopy (SEM) with energy-dispersive spectroscopy (SEM-EDS).

Microsamples were collected at UNIL’s Forensic Science Institute by Dr Nadim Scherrer of HKB|HEAB and Dr Stefan Zumbühl. They drew red, green and brown-black pigments from the terrestrial globe and red, green and yellow/green pigments from the celestial globe.

The report concluded that all the components identified by the analyses were available at the time the globes were manufactured (around 1540). The heterogeneity and mild chemical degeneration of the green pigments suggested either deterioration or the use of a mineral product.

Red pigmentsGreen pigmentsBrown-black pigmentsBinders

Terrestrial globe – bright red : lead red, traces of hematite

Celestial globe – dark red : litharge, lead red

Terrestrial globe – green : copper-based pigment tinged with chlorine (or degradation product containing chlorine)

Celestial globe – green : copper oxalate dihydrate

Terrestrial globe – brown-black printing ink : red/brown iron oxide : hematite, unidentified black phase

Celestial globe – brown-black printing ink : iron oxide, green copper pigments, gypsum

Terrestrial globe – red colour : proteins, resin (probably from the varnish); traces of oil cannot be ruled out (presence of lead carboxylates but the spectra overlap)

Celestial globe – green colour : oil, possible but unconfirmed presence of proteins (the spectra overlap)

Fabrice Ducrest © UNIL

Fabrice Ducrest © UNIL

In a step that was indispensable for restoration work, UV fluorescence was used by Prof Sebastian Dobruskin and Dr Nadim Scherrer of the Graduate School of the Arts in Bern (HKB|HEAB) to distinguish details of the spheres’ multi-layered surfaces. Various layers of varnish were detected which had been applied after the globes’ production. The celestial globe seems to have more surface varnish than the terrestrial one, which perhaps explains its better state of conservation.

Looking for watermarks

Besides UV fluorescence, infrared reflectography (IR) was used to try to detect any watermarks and thereby identify the paper component of the surfaces. Unfortunately, the thick layers of varnish prevented this altogether. IR nevertheless demonstrated that the globes’ surfaces had already been restored in the past and that the job had been well done.

At the Swiss Institute for Art Research (SIK|ISEA), Danièle Gros further analysed the globes’ structure using X-ray technology. This method highlighted a number of additional details of the terrestrial globe that rounded out the results obtained using tomodensitometry at the CHUV :

• the metal shaft (axis) crossing the inside of the sphere is encased in a wooden sheath ;
• the shaft is tipped at each end by a wooden calotte ;
• the layers of the sphere are made of (or reinforced with) pieces of cloth ;
• there is an “a”-shaped piece of metal next to the southern calotte, probably serving to fasten it to the layers of paper.

X-ray of the terrestrial globe (lower left: installation of the sphere and its position for the X-ray as seen from the machine placed one metre from the sphere. The film is just behind the sphere, pasted on the wall. The blue line indicates the position of the metal shaft and the red rectangle the area of the film). Visible on the film: the northern wooden calotte (green dots) seen almost sideways, the metal shaft (blue arrow) and wooden shaft (between the dotted yellow arrows); and the joint between the two hemispheres marked by the red arrows. © SIK|ISEA

X-ray of the terrestrial globe (left-hand illustration in detail): the white dotted arrows indicate the area recognisably formed by a piece of plain-weave cloth (though this is difficult to distinguish on the image). Apparently pieces of cloth were used like the papier mâché to help make the shells. © SIK|ISEA

X-ray of the terrestrial globe. Cross-section of the shell, slightly towards the outer edge. The sphere is made of numerous layers which are difficult to differentiate and tend to shred in places. The chalk-paste outer layers are denser than the inner ones, which are probably made of cardboard. © SIK|ISEA

© Laurent Dubois, BCUL

© Laurent Dubois, BCUL

Prof Reto Meuli and his team used computer tomodensitometry to make a series of 578 images of the terrestrial globe and 572 of the celestial globe. This scan of inert objects was a first for the Radiodiagnostics and Interventional Radiology department.

The images were made to better understand the inner structure of the spheres and prepare for their restoration. In a later stage they would also be used by the Swiss Institute for Art Research in Zurich (SIK|ISEA) to create a 3D simulation of the spheres.

On the other hand, the images that were processed with a view to analysing the origin of the wood of the stands in greater detail turned out to be unusable at the West Swiss Laboratory of Dendrochronology in Moudon. The scanner’s resolution was not suited to inert subjects such as globes.

Tomodensitometry revealed that the inner structure of the globes comprises the following components:

• a metal cross-shaft (axis)
• a hollow sphere made of two hemispheres
• hemispheres which are themselves composed of multiple layers but overall not thick at all

Terrestrial globe
Images made in June 2013 with tomodensitometry (CT scans) at the CHUV’s Radiodiagnostics and Interventional Radiology department.

Terrestrial globe - Portfolio of scans

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Celestial globe
Images made in June 2013 with tomodensitometry (CT scans) at the CHUV’s Radiodiagnostics and Interventional Radiology department.

Celestial globe - Portfolio of scans

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© Laurent Dubois, BCUL

© Laurent Dubois, BCUL

© Laurent Dubois, BCUL

In late June 2013, the globes were taken to the Radiodiagnostics and Interventional Radiology department of the Lausanne University Hospital (CHUV) for a series of tomodensitometry (CT) scans. The purpose of this probe was to determine the inner structure of the spheres and the state of conservation of the constituent materials.

This first major transfer raised the question of how to protect the globes generally during transport. Two safety crates were built to transfer them in the best possible conditions, protect them from dust and ensure stable levels of temperature and humidity.

The Cantonal and University Library of Lausanne funded the transfer and the safety crates’ construction by a specialist firm. These would continue to be used very frequently for all the globes’ later transfers and, of course, for their storage as well.

Eric Pitteloud © UNIL

Obviously a clear, coherent strategy was needed before analysing the globes any further. Experts at UNIL’s School of Forensic Science (ESC) were called for assistance.

A meeting was set up in late June 2013 with Prof Geneviève Massonnet, a chemist and expert on contemporary varnishes, and Dr Williams Mazzella, an expert on counterfeit money. They first of all put us in touch with experts at the Graduate School of Arts in Bern (HKB|HEAB) with whom UNIL collaborates, particularly for appraisals on ancient resins and colorants.

Secondly ESC’s expertise in photography was tapped to record digital images of the globes that could then be georeferenced to create a 3D simulation.