Glossary of terms

This glossary explains some of the technical terms you will find used within the site. It includes nearly 50 definitions, listed alphabetically, that describe parts of an artwork, types of damage, conservation processes, equipment and materials.

Abrasion

Paint loss caused by friction or use of paint dissolving solvents during varnish removal treatments.

Age cracks

Cracks through the whole thickness of the paint layer, caused by the natural movements of the canvas or through physical impacts to the paint layer. These begin to form as the painting ages and the paint layer dries and becomes more brittle.

Binder

The liquid part of a paint in which coloured pigment particles are suspended to form a paste, for example oils, glues and resins.

BEVA/EVA

Burger’s Ethyl Vinyl Alcohol – a modern, synthetic adhesive developed by Gustav Burger for use in conservation treatments, including lining and consolidation. A chemical mixture including solvents and polymers, providing good adhesive properties, long term stability and reversibility.

Blanching

Where a painting’s varnish has been damaged by water, degraded through age or partially dissolved with solvents, it can take on a whitish, clouded appearance, called blanching.

Bole

A soft, oily clay used as a pigment (especially a reddish brown pigment) in gilding. The bole is painted onto a surface before gilding, giving a subtle change in appearance to the gold leaf applied on top.

Canvas (linen)

Woven fabric made from flax. Traditionally used as the primary support material for oil paintings.

Canvas distortion

Bulges or wrinkles sometimes seen in an oil painting. These can be caused by the canvas losing tension on the stretcher and sagging at the corners. They can also happen where the canvas weave has been over stretched through impact or applied pressure.

Composition glue

Traditional lining adhesive made from a mixture of animal skin glue and flour. The moisture in the adhesive helps to re-adhere flaking paint but can cause the canvas to shrink. The components of the adhesive are biodegradable.

Conservation

A range of activities – including restoration – that aims to enhance and preserve works of art and other cultural artefacts for long-term benefit. These include stabilisation treatments, environmental control in display and storage areas, investigation and documentation, and ’cosmetic’ treatments such as cleaning and retouching.

Consolidation

A conservation treatment used to secure loose and flaking paint to a canvas. Traditionally animal skin glue or isinglass is warmed and applied underneath a loose paint flake with a brush. Once cool, it is re-warmed with heated spatula, allowing the adhesive to flow beneath the paint layer and into the canvas, securing the paint flake.

Craquelure

A pattern of cracks that develops on the surface of a painting as a result of the natural drying and aging of the paint layer.

Drying cracks

These cracks usually occur when a fast-drying oil paint is painted over a slow-drying oil paint. The fast-drying paint forms a skin, like a custard skin, over the underlying wet paint and movements in the painting cause the paint layers to tear. Often called alligatoring because the pattern of cracks is said to resemble alligator skin.

Drying oil

The binder in oil paint. Unlike most other oils, drying oils become hard and dry when exposed to air and light. They include linseed, poppy and walnut oils.

Facing

Where a light, non-woven tissue paper is glued to the surface of a painting to protect the paint layer. The tissue does not prevent physical harm to the paint layer, but it does hold it in position if it becomes detached from the canvas. This makes consolidation easier and reduces the risk of paint loss.

Filling

Replacing areas of missing paint in preparation for retouching. The surface provided through filling must be flush to the paint surface and mimic the texture of the surrounding paint. Materials used for filling include chalk and pigments, mixed with adhesives such as Mowiflex (a water based synthetic adhesive) or animal skin glues.

Gesso

Traditional ground for wooden panels and some early paintings on canvas. Gesso can either be coarse (gesso grosso), made by mixing chalk with animal skin glue or soft (gesso sotile), made by soaking gypsum in water for up to one month before mixing with animal skin glue.

Gilders Composition

A mixture of resin, whiting (fine chalk), and glue (animal skin glue), used instead of plaster of Paris for ornamenting walls and frames. It can be pressed into moulds or carved, before painting or gilding.

Gilding (oil)

The application of gold leaf to a surface using an oil-based medium that becomes tacky after it is applied to the surface. The thin layers of gold leaf stick to this medium.

Gilding (water)

The application of gold leaf to a surface using water mixed with a small amount of gelatine. The thin layers of gold leaf are attracted and held to the surface because of the weak hydrogen bonds in the water.

Glaze

A transparent layer of paint, either on its own or applied over layers of opaque paint. Traditionally used to add colour to compositions in monochrome opaque paint.

Ground

A coating or primer applied to a surface before painting to give uniform texture and absorbency. Used to prepare wooden panels or canvas for painting, gilding, or other decorative processes.

Hot-table

A large metal table which can be evenly heated from beneath for the purpose of lining a painting.

Impasto

A technique of applying oil paint thickly to build up the impression of texture or form.

Interleaf

An interleaf is sometimes used in lining treatments, both to increase the structural strength of the lining canvas and to reduce the possibility of weave interference during the lining. The interleaf is placed between the lining canvas and the original canvas.

Isinglass

An adhesive made from the swim bladders of sturgeons, cleaned and boiled until the collagen from the bladders is dissolved. The resulting adhesive forms a colloidal suspension, meaning that when warm it is a liquid, but when cool it is a gel.

In-painting

Where new paint is applied only to areas of fill and paint loss. The retouching paint does not encroach over areas of original paint.

Lining

Attaching new canvas to the back of the original painting canvas with adhesive. This adds structural stability to fragile paintings, and reduces the tension and detrimental forces acting on the paint layers.

Linseed oil

The most commonly used drying oil binder for oil paints. Made from flax seeds, linseed oil can yellow after prolonged exposure to light. Walnut and poppy seed oils discolour less, but are less commonly used.

Medium

See binder

Over painting

A retouching technique where new paint is applied to areas of fill and paint loss, and in some cases over original paint. This is done to improve the overall clarity of the painting by to reinforcing areas where the paint has worn thinner.

Paint layer

The paint layer is the actual layer or layers of colour applied by the artist in the execution of the painting.

Pentimento

”Ghost” images that appear in areas of a painting where the artist has changed parts of the composition or painted out sections. Oil paint becomes more transparent as it ages, making the underlying images gradually more visible.

Pigment

An insoluble substance that gives a colour to a binder or mixture and always appears as the same specific colour when viewed in white light.

Poultice

A method/material used to remove hardened water-based adhesives. The poultice is a mixture of water and powder (synthetic or organic). The powder expands in water, forming a clear gel that is placed over the hardened adhesive. The gel ”holds” the water against the adhesive, preventing evaporation or penetration of the painting.

Primer

See ground.

Restoration

A range of treatments intended to return cultural property to a known or assumed state, often through the addition of nonoriginal material. These treatments include cleaning, filling, retouching and varnishing.

Retouching

Where new paint is applied to a prepared surface to replace areas of loss or damage in a painting.

Size

Layer of animal skin glue applied to the canvas before the ground and paint layers. The size dries to fix the fibres of the canvas in place. It also roughens the surface, which helps the ground layer to adhere to the canvas.

Solvent

A liquid used in conservation to dissolve either natural or synthetic resin varnishs on a painting without damaging the paint layer.

Strainer

Wooden framework around which a painting’s canvas is stretched. A strainer is a fixed rigid structure that cannot expand.

Stretcher

Wooden framework similar to a strainer, but with the corners unfixed. The framework can expand in size by tapping small wedges of wood into corner channels. This means the painting can be kept at the correct tension.

Strip lining

Attaching wide strips of new canvas to the outer edges of a painting in order to increase the strength of deteriorated tacking edges.

Synthetic

A man made organic substance (containing carbon) made through the chemical reaction of simple molecules.

Tacking edge

The outer edge of a canvas that is stretched or wrapped around a wooden framework and secured to this with tacks or staples. This edge is easily damaged through handling and by the tacks that secure it.

Vacuum envelope

Used during lining treatments to ensure that the layers of lining canvas, adhesive and painting remain in close contact. The vacuum envelope is a ‘bag’ of Melinex wrapped around a large wooden frame, into which the painting and lining canvas are placed. Air is then sucked out of the bag to create a vacuum.

Varnish

A solution of a resin in a solvent or a drying oil which, when spread out in a thin film, dries and hardens by evaporation of the solvent, or by the oxidation of the oil. Applied as a protective coating or to enhance the appearance of the surface underneath.

Wax-resin

A facing adhesive made by melting beeswax into a natural or synthetic resin.

Weave Interference

An increase to or disruption of the canvas weave texture seen in the paint layer. This can happen if the lining canvas is pressed into the back of the painting whilst on a hot table during lining treatments. The use of a vacuum envelope or interleaf can reduce this effect.