In fact, Mercator himself was an artful engraver and mastered every stage of the globes’ production, from design to delivery. No other globemaker would ever match this expertise.

Terrestrial globeCelestial globe

© Royal Library of Belgium, reproduced with permission

© Royal Library of Belgium, reproduced with permission

© Royal Library of Belgium, reproduced with permission

© Royal Library of Belgium, reproduced with permission

Five printing plates were engraved to make the terrestrial globe. Four of them were divided into a total of twelve gores rendering the geography of the Earth, with each gore covering 30° longitudinally. The fifth printing plate bore the two circular calottes capping the poles plus the horizon ring, 5 cm wide, itself divided into four segments.

© Royal Library of Belgium, reproduced with permission

© Brussels: Royal Library of Belgium, 7 D 148 (RP), reproduced with permission

© Royal Library of Belgium, reproduced with permission

© Royal Library of Belgium, reproduced with permission

© Royal Library of Belgium, reproduced with permission

© Royal Library of Belgium, reproduced with permission

© Royal Library of Belgium, reproduced with permission

© Brussels: Royal Library of Belgium, 7 D 148 (RP), reproduced with permission

These copper plates were used to produce globes for decades in Mercator’s workshop, no doubt for over 40 years, without ever being updated or copied. When Mercator died in 1594 the plates devolved to his son Rumold, who continued his father’s business in Duisburg. Rumold in turn died in 1600, leaving several minor children who were advised to sell the engraved plates. It was the children’s guardian who bought them in 1604 and then sold them that same year to Jodocus Hondius, an engraver and publisher of maps in Amsterdam.

When Hondius died in 1612 the plates devolved to his son and to his son-in-law, Joan Blaeu, another printer and cartographer based in Amsterdam. It is assumed that all the plates were lost in the fire that destroyed Blaeu’s printing press on 23 February 1672.

Although the plates are gone, a set of printed gores, purchased by the Royal Library of Belgium in 1868, has survived. The only known original prints in Europe, they were used to make facsimile reproductions of Mercator globes for the 1875 Geographical Congress in Paris. In 1968 an atlas published in Brussels showed the entire set of Mercator’s gores, including the calottes and horizon rings.

The round wooden base, 42.5 cm in diameter and 3 cm thick, sits inside the four balusters and is glued to the four rectangular feet. This circular base, the rim of which is moulded, is made of three planks in the case of the celestial globe and four for the terrestrial one. A small circular support 2.8 cm in diameter and 1.6 cm high sits on the centre of the circular base and is notched to hold up the copper meridian. Several layers of paper serve as a joint between this small support and the main one underneath.

A small compass with an hour dial in Roman numerals is set into the circular base along the rim under the copper meridian. This compass is square shaped in the case of the terrestrial globe and octagonal in the case of the celestial one.

The surfaces de the circular base and the balusters bear painted illustrations. The design can no longer be identified but it could be a red and green false-marble type of decoration. A light layer, probably applied originally, served as a base coat. The feet and the moulded edges of the horizon ring and the circular base are painted black.

X-ray of the stand of the terrestrial globe (image reconstructed from four plates). The light preparatory layer was laid irregularly, perhaps originally, and is distinguishable with X-rays (it may contain lead white). The growth rings of the wooden stand can also be seen clearly. Metal screws (recent, two in each foot) appear white. (Ill. 22, SIK|ISEA report)

The inner side of the celestial globe reveals an earlier restoration.

Celestial globe, inner side of the stand. The positions of the feet are marked with pink chalk. The stand was taken apart and glued back together during an earlier restoration. The wooden dowel (or trunnion) in the left-hand image was replaced with a new one (Ill. 23 & 24, SIK|ISEA report)

The stands’ undersides bear various labels:

Terrestrial globeCelestial globe

Glued label

History of Science Museum, item number
with the hand-written reference Lausanne.

Glued label

History of Science Museum, item number 54
with the hand-written reference Observatory

Etiquette en plastique vert

VD

Hand-written reference

2 Coeli

L’inscription a été tracée au pinceau, à l’encre ou à la peinture noire. Le mot latin “coelus” ou “caelus”, ici au génitif, signifie le “ciel”. Cette inscription permettait peut-être de distinguer ce socle de celui du globe terrestre.

Two notches cut deeply into the wood hold the copper meridian in place.

Between the paper layer and the wood there is a thick layer of charged adhesive (or a thin preparatory layer). The surface of the paper is partly coated with natural-resin varnish. This does not cover all the horizon ring: on about 1.5 cm from the inside (the part with the inscriptions of the horoscopes and days), a band is unvarnished. The limit of the varnish is not very precise, suggesting that it is not an original varnish.

Close-up photo of the horizon ring of the celestial globe under UV fluorescence prior to restoration. The varnish fluoresces strongly whereas the unvarnished band towards the inside of the ring (above the yellow arrow) does not fluoresce. We can see that the varnish is very worn. The glue spilling over the joint from a previous restoration (red arrow) is also enhanced under UV fluorescence. © SIK|ISEA

While the total thickness of the spheres’ walls is difficult to determine, it is estimated to be more than 1 cm at least (as measured by a hole that does not completely cross the shell). The two cardboard half-shells were probably formed on half-balls of wood covered with soap so they could be easily detached after drying, a technique described by Denis Diderot and Jean d’Alembert in their Encyclopaedia (1751-1772). The half-shells were then pasted to form a sphere. The joint can be seen in both the CT scans and X-rays in the form of a denser white line.

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). On the film we can see 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 in the image). Apparently pieces of cloth were used like 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

The multiple layers comprising the structure of the sphere were covered over with chalk and proteic paste, forming a smooth, homogeneous surface onto which the gores could be affixed with starch glue. There were twelve of these gores, or segments, extending to the 70th parallels, with each polar region capped by a round paper calotte.

The printed gores were coloured using paints made with various binders. For protection, the surface of the paper was then coated with varnish made from natural resins.

Each hollow sphere is crossed by a metal shaft, probably made of brass, itself inserted in a wider wooden shaft. At each end inside the sphere a calotte, also made of wood, helps distribute the pressure from this axis for better balance when the globe is rotated.

In the terrestrial globe, X-ray and CT scan imaging pointed up a curious little piece of metal shaped like an “a” roughly 1 cm2. It is very close to and possibly even inside the southern wooden calotte. Its purpose is not very clear but it could be a system for fastening the wooden calotte to the sphere.

X-ray of the terrestrial globe. In the red circle, a little piece of metal shaped like an “a” sits very close to (possibly on or in) the southern calotte. The dashes are tiny nails, invisible from the surface of the sphere. It is difficult to determine whether these nails are originals or not. The blue line indicates the position of the metal shaft and the red rectangle the area of the film. The wooden shaft runs between the yellow arrows. © SIK|ISEA