Producing a cast:
making an imprint using casting and patina

Making an
imprint

The casting
process

Creating
the patina

Casting is the faithful recreation of a work of sculpture and is the result of a long and meticulous process that involves creating a mould and then using it to obtain multiple reproductions.
Making a imprint
Making a physical imprint
Silicone elastomer for the Farnese Hercules cast
The artisans of the Rmn-GP casting studio make imprints from original artworks. A protective layer is first applied over the entire piece. The statue caster then uses a brush to apply two layers of liquid elastomer. This membrane is made up to around one centimetre thick, depending on the shape being cast. The advantage of this material is that it is elastic, precise and easy to unmould.
Creating the mould
Once the shape is covered in its silicone membrane, all the layers of plaster coating are produced for the different parts of the mould. These hold the silicone in place once the piece is unmoulded. A wooden frame finishes the process, to support the coating and help with unmoulding and the handling of the mould. Once the mould is finished, the artwork is unmoulded. This is the most delicate step, as any mistake when handling could damage the original.
Unmoulding
Making a 3D imprint
The casting studio also puts its digital technology to use by producing 3D imprints, which have the dual advantage of avoiding direct contact with the artwork and making enlargements and reductions possible. As the definition of the surface offers less precision than silicone elastomer (a difference of 5 microns for a physical imprint versus 200 microns with the use of 3D), digital technology is only used when the original artwork is fragile, or if a change in the format of the reproduction is sought.
Producing the 3D digital model of Pompon’s Bear
The casting process
The Réunion des Musées Nationaux – Grand Palais Casting Studio has some 6,000 moulds used for casting in plaster, resin, terracotta and bronze. Slush casting is the most frequently used technique. Plaster is applied to the mould in thin layers, the first using just plaster, the second reinforced with oakum. A wooden or metal frame is produced to support and strengthen large pieces.
Unmoulding
When the plaster has set, the cast is ejected from the mould. The piece has various “seams” from where the different parts of the mould have been joined together. These are trimmed and then made uniform with the rest of the model to ensure that no traces of the production process are visible.
The patina
Bronze-effect patina
The final step in producing a cast involves applying a patina to the raw material to create a surface effect that is as close as possible to the originals, lending it the appearance of marble, terracotta, bronze etc. as well as reproducing an aged effect.
The Rmn-GP Casting Studio employs a team of patineurs who are experts in this art form. Creating a patina always involves a close inspection of the original to ensure that the result is as accurate as possible. The patineurs work with museum curators to verify the reference model.
Marble-effect patina
Read a full article on our work published in the Revue des Patrimoines.