Revelation - information about the Reveal gallery objects

The replica head was made specially for display in Reveal. The original sculpture came into the collections of National Museums Liverpool in 1964, when it was donated by the then owner of Norton Priory. The St Christopher statue has been displayed at Norton Priory since 1981. Since 1999 it has been in a purpose-built gallery.

Pigmentation

When the St Christopher sculpture came into the sculpture conservation studio here at the National Conservation Centre in 1996, close examination revealed tiny remains of the statue’s medieval polychromy. The colossal saint would have been a striking vision in his vermillion cloak, flesh coloured skin and dark grey beard. We wanted to recreate a possible colour scheme on a small section of the St Christopher sculpture.

The whole of the St Christopher sculpture was scanned using a laser scanner. We then took the virtual model that made up the head, scaled it down slightly and used the data to create this replica head using a technique called sand printing. The replica head was then coated in a layer of gesso to seal the surface before conservators applied pigments. Finally a glaze was applied to the pigmented surface.

Laser scanning the Norton Priory St Christopher took us a week and the post-processing of the data took us 200 hours. It took conservators 20 hours to re-pigment he replica head.

Laser scanning

Triangulation based laser scanners project a thin stripe of low-power laser light onto the surface of an object. An off-axis digital camera records the reflected light. As the angle between the scanning beam and the sensor is known, the location of points along the stripe of light can be calculated. Under ideal conditions, the resolution and accuracy of our systems is less than a millimetre.

While the raw data (millions of points) obtained by 3D laser scanning does provide the information required for some applications, usually this 'point cloud' is converted to a wire frame mesh.

This polygon mesh data is then post-processed to prepare it for its end use. Post-processing includes filling holes (caused by areas of the sculpture which we couldn’t reach with the laser scanner, such as the inside edge of a finger) and cleaning-up the data. Polygons that are inverted or crossing one another can arise during the complex calculation performed by software during the meshing process. Unclean areas of data can also be a result of scanning dark, shiny or crystalline surfaces that absorb the laser beam, or reflect it specularly.

We also decimated (reduced the number of polygons that make up the surface) the large model of the St Christopher sculpture. Areas of low detail can be made up from larger, and therefore fewer, polygons than areas of high detail, which require a denser mesh to define them. In this way the overall file size can be reduced, although care must be taken not to lose resolution or detail by over-decimation of a data set.

Recording in 3D can produce detailed archives of important objects. The virtual image recorded is not light subjective (as is the case for photographs). In fact, the image can be lit from any angle. This means that we can examine surface details closely. Data can be transferred easily between institutions around the world, allowing access for a wide audience to objects that cannot be moved.

The data produced by laser scanning can also be transferred into virtual environments. This means that objects can be placed into a historical context in computer simulations. Historical context simulations can show us what sort of surroundings a sculpture or object may have been in when it was first created, often centuries ago. Such images are often used in museums or on television programmes. Objects from around the globe can be brought together in 'virtual galleries'.

We can also use the data we collect by laser scanning to create replicas using milling machines, where the tool path of a drill is controlled by the data we created as it cuts the surface of a material, or by using 3d printing. 3D printing is a layer manufacturing technology in which the layers are formed by using a print head-like device to distribute an adhesive to bond the surface of a powder in the desired shape. The digital model we create determines the size and shape of the layers.

Sand printing

Sand printing is a layer manufacturing technology in which the layers are formed by using a print head to distribute a sticky resin to glue the surface of sand in the shape determined by the digital model we create. We used sand printing to create the replica of St Christopher’s head because the original sculpture is made of sandstone. Sand printing gave us an object that is lightweight but with a similar surface finish as the original material.

The Norton Priory St Christopher

The mediaeval sculpture of Saint Christopher on display at Norton Priory is twice life size. Noone is sure exactly when it was made but from the style of the statue art historians believe that is was probably carved between 1375 and 1400. What is remarkable about this sculpture is that it has survived at Norton Priory through the reformation and political upheavals of the 16th and 17th centuries.

The sandstone is in outstanding condition and it is one of very few examples in Britain of colossal religious figure sculpture. Its importance nationally lies in what it reveals about the high quality of medieval sculpture from the north of England in the late 14th century.

The statue is 3.37m tall and is carved from local red sandstone. In the 14th century there was a quarry a mile from Norton Priory at Windmill Hill. The quarry belonged to the priory and was probably the source of the stone from which the priory and the sculpture were built. The statue shows St Christopher, in medieval dress, carrying the child Christ through a fish-filled river. The fish, which are carved naturalistically, are Garfish, Pike, Mullet, Carp or Bream, and Plaice or Flounder. Only one fish, with spikes on its back, is not based on a real species of fish.

The statue is likely to have been carved at Norton Priory but no one knows the identity of the sculptor. This is common for much mediaeval sculpture because of the relatively low status of medieval craftsmen in Britain. In addition, there are hardly any surviving records from the time most of them were destroyed during the Reformation.

The sculpture was conserved at the National Conservation Centre during 1996-1997. Before returning to Norton Priory it went to London to go on display in a Tate Britain exhibition of mediaeval sculpture called Image and Idol, in 2001-2002. The sculpture is now on display in its own gallery at Norton Priory that shows it in its full glory and examines its history.