Plaster cast of a relief depicting the Incredulity of St Thomas made in Spain, 1926. The original was made in about 1100.

Plaster cast of a relief depicting the Incredulity of St Thomas on a pillar from the cloister of the Monastery of Santo Domingo de Silos.

Cast of a relief made in plaster in Madrid, 1926 and depicts the Incredulity of St Thomas and was acquired in exchange from the Museo de Reproducciones Artisticas, Madrid in 1926. The original was made by an unknown artist in stone in Madrid about 1100 and is from the cloister of the Monastery of Santo Domingo de Silos.

Making plaster copies is a centuries-old tradition that reached the height of its popularity during the 19th century. The V&A's casts are of large-scale architectural and sculptural works as well as small scale, jewelled book covers and ivory plaques, these last known as fictile ivories.

The Museum commissioned casts directly from makers and acquired others in exchange. Oronzio Lelli, of Florence was a key overseas supplier while, in London, Giovanni Franchi and Domenico Brucciani upheld a strong Italian tradition as highly-skilled mould-makers, or formatori.

Some casts are highly accurate depictions of original works, whilst others are more selective, replicating the outer surface of the original work, rather than its whole structure. Like a photograph, they record the moment the cast was taken: alterations, repairs and the wear and tear of age are all reproduced in the copies. The plasters can also be re-worked, so that their appearance differs slightly from the original from which they were taken.

To make a plaster cast, a negative mould has to be taken of the original object. The initial mould could be made from one of several ways. A flexible mould could be made by mixing wax with gutta-percha, a rubbery latex product taken from tropical trees. These two substances formed a mould that had a slightly elastic quality, so that it could easily be removed from the original object. Moulds were also made from gelatine, plaster or clay, and could then be used to create a plaster mould to use for casting.
When mixed with water, plaster can be poured into a prepared mould, allowed to set, and can be removed to produce a finished solid form. The moulds are coated with a separating or paring agent to prevent the newly poured plaster sticking to them. The smooth liquid state and slight expansion while setting allowed the quick drying plaster to infill even the most intricate contours of a mould.
Flatter, smaller objects in low relief usually require only one mould to cast the object. For more complex objects, with a raised surface, the mould would have to be made from a number of sections, known as piece-moulds. These pieces are held together in the so-called mother-mould, in order to create a mould of the whole object. Once the object has been cast from this mother-mould, the piece-moulds can be easily removed one by one, to create a cast of the three-dimensional object.

The original limestone sculptures formed parts of the piers, or pillars, from the Benedictine monastery of Santo Domingo de Silos, a Romanesque building admired for its architecture and sculpture.

The biblical scenes depicted are The Incredulity of St Thomas and the Pentecost. These casts are not painted and so they more or less reflect the appearance of the sculptures as they looked in the early 20th century, when their original bright colours had been lost.

REPRO.A.1926-14