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Glossary

Glossary

Bole

Bole is a clay-like substance which is red, brown or yellow in colour. It is a mixture of water and glue and is painted on to a gessoed frame to form the undercoat for the application of gold leaf.

Colophony

Colophony (also called rosin) is a dried and cleaned part of the resin obtained from conifer trees. It is a brittle and transparent brownish or yellowish substance added to 'composition' to make the mixture elastic. (Rosin is a specific type of resin.)

Compo

Composition, or compo, is a traditional picture framing material which is used as an alternative to carving to make decoration on frames. When heated, compo is soft enough to be pressed into decorative moulds. When cooled it becomes hard and durable. Compo is made from animal (hide) glue, whiting (chalk), linseed oil and colophony.

Conservation

Conservation is an umbrella term for the profession that is responsible for the physical care and technical analysis of cultural material and its environment. Conservation activities include restoration, preservation, examination, research, advice, treatment, preventive conservation and training.

Cornice

Cornice refers to the set of crowning moldings that cap an entablature.

Entablature

Entablature refers to a classical architectural element such as that found in a Greek temple, which rests horizontally above the columns. It is commonly divided into architrave (the part immediately above the column), frieze (the central space), and cornice (the upper projecting moldings).

Gesso

Gesso is a mixture of ground chalk and animal glue traditionally used on wood as a preparation layer prior to oil painting and gilding.

Infra-red reflectography

Infra-red energy is heat, and it occurs at wavelengths longer than 760 nanometres - just beyond red in the electromagnetic spectrum. Infra-red imaging relies on the selective absorption of heat by pigments and is most useful for detecting underdrawing. Many earth-based pigments (for example, charcoal in drawing layers) are visible using an infra-red detector. At the Queensland Art Gallery we use a Hammamatsu Vidicon™ system.

Paint cross-section analysis

Sometimes it is possible to remove a small chip of paint from the edge of a painting using a microscalpel. This chip of paint (usually less than ½ mm in diameter) can be embedded in polyester resin and cut through as a cross-section to reveal important information about paint layers, the artist's technique, and the age of pigments used. These samples can be analysed using optical microscopy in normal light and ultra-violet illumination and imaged up to 100 000x using a scanning electron microscope (SEM). Inorganic pigment analysis can be undertaken using energy dispersive X-ray microanalysis (EDX) through the scanning electron microscope (SEM). Various organic analysis methods including fourier transform infra-red spectroscopy (FTIR) are also available.

Pediment

A pediment is the top element of a tabernacle frame; it may be triangular, semi-circular or broken.

Predella

Predella is the platform or step on which an altar stands. In painting, predella refers to the paintings or sculptures running along the frame at the bottom of an altarpiece. They often consist of narrative scenes, for example, scenes in the life of a particular saint.

Pre-Raphaelites

The Pre-Raphaelite Brotherhood was a group of English painters, poets and critics, founded in 1848.

Preservation and preventive conservation

Preservation and preventive conservation involve activities that aim to protect or maintain an art work in its current condition ― that is, to minimise chemical and physical deterioration or loss of information. This can include individual treatment on an art work such as rehousing photographs, as well as activities such as establishing a stable environment and determining procedures for handling, packing and transport.

Restoration

Restoration is defined as treatment that aims to return an art work to a known earlier state. Establishing the authenticity of a known state is a key part of this activity and often involves technical and other research.

Sight (edge)

Sight (edge) refers to that part of the frame moulding nearest to the framed object.

Tabernacle

Tabernacle frames are based on classical aedicular architecture. An aedicular frame is classical in style and is characterised by an opening framed by two columns, with a decorated entablature lying horizontally above the columns, and usually with a pediment forming the top element of the frame.

Taenia

Taenia refers to the flat, undecorated, raised band of moulding on a frame.

Ultra-violet photography

Ultra-violet light is short wavelength energy, just beyond violet in the electromagnetic spectrum and invisible to our eyes. Many materials show autofluorescence when exposed to ultra-violet light. Aged natural resin varnishes characteristically fluoresce a greenish colour, and new oil paint remains dark under ultra-violet light, so the placement of new additions on top of old varnish can often be detected using ultra-violet inspection.

Water/oil gilt

Water/oil gilt is the application technique where gold leaf is applied to a gesso and bole base using water as the mordant or glue. Water gilt surfaces are able to be highly polished compared to oil gilt surfaces (oil used as mordant) which cannot be polished.

Visible light photography

Visible light is the part of the electromagnetic spectrum which is visible to the human eye ― colours from red to violet make up 'white' light. Works can be photographed in normal, raking (oblique) or transmitted (lit from behind) light to show up different characteristics.

X-radiography

X-rays are the part of the electromagnetic spectrum invisible to the eye and useful for mapping materials of different atomic weight. The larger the atoms from which a material is made, the whiter that material appears on an X-ray film. X-rays are particularly useful for imaging lead white design areas in paintings, and metal armature inside sculpture. There are conservators licensed to undertake radiography of art works at the Queensland Art Gallery.