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 treatments & materials 


conservation & restoration terms


Damage to one or more paint layers, resulting from rubbing, scraping, or other wear.



Deposit on the surface of a painting, for example dust, fly spots, food splatters.


Active flaking

Paint and/or ground which is lifting and may be about to flake off.


Age cracking

Pattern of cracks caused by aging or movement. On canvas paintings they usually occur overall, may penetrate all layers of the paint, and sometimes appear as darkened impressions on the back. On wooden supports cracking usually forms a grid-like pattern along the grain.

John Golding J7 Epiphany 1989, detail, private collection


Narrow wooden strips attached to the back of wooden panels, across the grain, to lend extra rigidity to the structure and/or hold together cracked or joined panels.


BEVA 371

Synthetic adhesive which is used as a consolidant and/or as a lining adhesive.


Binding medium

See medium.



Bloom on an unvarnished painted surface.


Blind flaking

Separation within a layer, or between layers of paint and ground which is not yet in danger of flaking off.



See blind flaking



White or bluish-white cloudiness that appears on varnishes, caused by penetration of the layer by moisture or pollutants.



Distortion of a canvas painting, caused by shrinkage or compression, or movement of the wooden stretcher. Often seen as folds or wrinkles in the corners of paintings. Will eventually cause damage to paint and ground layers. See also draw.



Small bow-shaped wooden battens adhered to the back of wooden panels, usually to hold cracked, or jointed sections together.



Woven fabric on which a picture is painted. Also called the support. Usually made of linen, cotton or hemp.



Paint which appears to be becoming powdery and may look whitish. It is the result of insufficient binding medium in the paint and some pigment may be lost. Caused either by the artists poor technique or subsequent damage to the paint layer.



An incomplete split in wood, running along the grain.



Process of removing surface accretions such as dust, dirt, varnish, fly spots or overpaint from a painting.



See flaking.


Condition Report

A Condition Report is prepared by a conservator, for a client, describing a painting, or object and the condition it is in at time of examination. See also Frequently Asked Questions.



Steps taken to stabilize, preserve and protect an artwork for as long as possible.


Corner draw

Wrinkles or distortions which form in the corners of stretched paintings on fabric. See also buckling.


Cotton duck

Woven canvas support which is made of cotton.



See craquelure; age cracking & drying cracks.



Grid-like arrangement of wooden battens on the back of a wooden panel. A cradle may or may not be structured to allow some movement of the panel.



Generic term to describe cracking. Specifically, see age cracking; drying/traction cracks;Sigmoidal/mechanical cracks; crazing.



Very fine pattern of cracks.



Wooden members of a stretcher or strainer which form one or more crosses between the four outer members. Used to lend greater rigidity and to improve tension.



Areas of paint and/or ground which form cups or islands, with their edges lifted and raised. Severely cupped paint can distort the support.



See cupping.



Liquid, such as water or turpentine, which is used to dilute paint.



See corner draw.


Dry rot

Timber decay caused by fungi. The cellulose in the wood is consumed, leaving a soft, weak skeleton.


Drying cracks

Cracks, often very wide, in the paint, ground and/or varnish layers that resemble alligator-skin or orange peel. They occur when a quick-drying (or lean) layer over a slow-drying (fat) layer.



Cotton canvas painting support, see cotton duck.


Easel painting

Painting on canvas, wood, metal, paper or some other portable support.



Powdery surface crust formed when substances in plaster or varnish crystallize upon contact with air.


Egg tempera  

See tempera.


Estimate of Costs

An Estimate of Costs is prepared by a conservator, for a client, outlining the cost of proposed conservation and/or restoration treatment. See also Frequently Asked Questions.


Fat paint 

Paint which has a high ratio of medium to pigment, and little diluent, making it very elastic but slow-drying.


Fill / Filler / Filling

Where paint and ground have been damaged and lost it is usually necessary to insert a filler so that the area of loss becomes level with surrounding paint. All fillings should be readily reversible.



Loss of adhesion between any or all layers of paint, ground and support. In active flaking paint and ground has started to fall off.


Fourier Transform Infrared  Spectroscopy (FTIR)

Form of microscopic analysis (of samples as small as 10 microns) used for the classification of organic compounds and some inorganic pigments.



Brown or reddish spots on paper and card, caused by mould or the oxidation of iron particles.



Outer framing device, often gilded or decorated, which is not part of the painting but may have been made or commissioned by the artist. Not to be confused with stretchers or strainers.



Wall-painting technique which entails working directly onto wet, freshly applied plaster.



Ground layer, made of animal glue mixed with chalk, applied to the support, to form a surface on which to paint (usually in egg tempera), or apply gilding.



Material applied to a support, on top of the size, to prepare it for painting. It is usually comprised of one or several layers of gesso or oil paint. See also priming.



Thin, translucent layer of paint, used to tint the layer/s of paint beneath it.



Refers to the protective glass or Perspex positioned in front on a painting, within its frame.



Subjective term used to describe the relative shininess, or degree of specular reflection, of a surface.


Glue size

See size.



Texture of the painted surface, created by the strokes of the brush or palette knife. Impasto is more obvious in thick, heavy paint, as troughs and peaks, but the term also applies to the strokes used to create smoother surfaces.


Incipient flaking  

Paint sections or layers which have separated but have not yet begun to fall off. See flaking.


Infrared Reflectography

Imaging technique for investigating underdrawing. Infrared light penetrates upper layers of paint to be absorbed by the underdrawing. This absorption can then be captured by infrared-sensitive camera film.



See retouching/inpainting.



Flat, triangular, wooden wedges inserted into slots at the corner joints of a stretcher. They driven into the slots, by degrees, to expand the stretcher.


Lean paint

Paint which has a low ratio of medium to pigment or a high proportion of diluent, making it non-elastic but fast-drying. See also drying cracks.



When a new canvas is adhered to the back of a canvas support which has become badly damaged by tears, or has lost its elasticity and become brittle. Also known as re-lining.



Area of missing original paint, ground and/or support.


Mechanical cracking

See Sigmoidal cracking.



Substance which is used to bind the coloured material in paint. Some examples of binding media are oil, wax, casein, egg yolk and resin.



Wall-painting executed onto dry plaster (or on some other support, which is then attached to the wall). Typically painted in oil, casein and glue-size mediums.


Oil paint

Dry, finely-ground pigment which is made into a paste with an oil, such as linseed, poppy or walnut. The paste may then be diluted with more oil and/or a spirit such as turpentine or white spirit.



Those parts of a work of art which are thought to date from the time of its execution, having been applied by the artist or, under his or her direction, by members of his or her studio.



Paint, of later application, which partially covers original paint. It may have been applied at any time after the completion of the picture. Such paint was often applied by restorers in the past as an easy way to cover and disguise damages.



Mixture of coloured matter called pigment and a binding medium such as oil, wax, egg yolk, gelatine, acrylic etc.



Painting executed on a solid support, typically made of wood, metal, ivory or glass.



Paint may become increasingly translucent with age and the lower layers may become visible through the upper ones. Typically, underdrawing or changes to the composition may be seem clearly with the naked eye. An Italian term.



Highly magnified image of part of a painting, taken with a camera attached to a microscope.



Coloured material which is finely-ground and then mixed with a binding medium for use as paint. Pigments can be organic or inorganic and are made from mineral, vegetable or synthetic sources.


Polarized Light Microscopy (PLM)

Microscopic examination used to identify pigments and fibres.



Support is traditionally primed with a layer of animal-glue size, followed by one or more layers of ground, on top of which the painting is executed. See also size and ground.



See rebate.


Rabbit skin glue

See size.


Raking light

A light source is placed to one side of the painting at a low angle to the surface, so that it rakes across the painting. This this technique is used in examination and photography to reveal surface distortions, such as raised paint or undulations.



Cut-away groove at the back of the inner edge of a picture frame, which is intended to receive the painting and hold it in place.


Recommended Treatment Report

A Recommended Treatment Report is prepared by a conservator, for a client, describing what is required to preserve, stabilize and/or repair a painting, or object. See also Frequently Asked Questions.



Canvas painting which has already been lined may be re-lined after removal of the old lining material and adhesive. This may be done when the existing lining or glue has become degraded or damaged.



Category of solid or semisolid, viscous substances, both natural (mastic, amber, copal) and synthetic (polyvinyl, polystyrene). Resins have been important ingredients in varnishes, adhesives and paints.



Repair to artworks that have suffered loss, weakened supports, water, fire, insect and other chemical and physical damage or deterioration



Replacing or disguising areas of lost paint by matching the tone and/or colour of the original paint surrounding the loss. Retouching materials must be inert and reversible and not extend beyond the area of loss.



Conservation ethics demand that all materials and processes used by the conservator should be easily reversed or removed, causing no damage to original material in the process.



Thin layer of semi-opaque paint used to modify a colour already applied.


Sigmoidal/mechanical cracking

Sigmoidal cracks are those which may result from a blow to a canvas painting. They form a concentric circular pattern which resembles a cobweb. If the canvas has been scratched or rubbed from behind the mechanical cracks may resemble a feather.



Glue layer applied to a support to promote adhesion between it and the ground layer. Traditionally rabbit skin or some other animal skin glue is used.



Plain frame, usually of wood, over which fabric canvas is stretched to form the support for a painting. A strainer does not have keys so its size cannot be adjusted once the canvas is stretched over it. See also stretcher.



Plain frame, usually of wood, over which fabric canvas is stretched to form the support for a painting. Unlike a strainer, a stretcher has Keys in its joints, which are used to expand it once the canvas is stretched over it.


Stretcher bar mark

An impression of the stretcher visible on the surface of a canvas painting. These appear as fairly continuous, parallel, straight cracks in the Paint and Ground layers, and usually occur when a canvas painting is slack on its stretcher.



Material on which a picture is painted, such as canvas, wooden panel or plaster-covered wall. Auxiliary structures, such as stretchers are also referred to as secondary supports.


Surface dirt

Loose dust or impacted dirt on the surface of a painting or object.


Tacking edge

Part of a fabric canvas support which is folded around the stretcher or strainer and secured there with tacks or staples. It may be primed and/or painted.



Paint which is comprised of finely-ground coloured pigment mixed to a paste with water, then combined with egg yolk as a binding medium. Tempera may be diluted with water.



Paint and/or ground which has started to flake and has moved outwards from the support to form pitched tents. Tenting is usually the result of changes in the dimensions of the support, such as canvas shrinkage.


Traction cracking

See drying cracks.


Transmitted light

A light source is placed behind a canvas painting. The light is transmitted through paint losses, cracks, tears, and thinly painted areas and the technique is used to identify possible points of weakness.


Ultraviolet (UV)

Paintings may be examined using UV light. Some painting materials and varnishes exhibit characteristic fluorescence colours which may used to identify them. UV light may also identify areas of retouching.



Preparatory drawing which is subsequently covered with paint. Drawings are often executed in graphite, charcoal, paint or chalk, using a pencil, pen or brush.


Vacuum table

Plate with a suction device and sometimes a heating element. Used to treat deformations in supports or to line paintings through the application of gentle, even pressure and/or heat.



Protective coating applied to the surface of painting. There are a wide variety of varnishes, made of combinations of resin, spirit, oil and wax.



Picture which is painted directly onto the surface of a wall or onto another support, such as canvas, which is attached to the wall. Frescoes and murals are examples of wall-paintings.



Paint which is a combination of very finely-ground coloured pigment mixed to a paste with water and gelatine. The moist paste is put in tubes or allowed to dry in small pans. The paint is diluted with water and applied onto supports such as paper.



Used to examine paintings to reveal changes to the composition by the artist and subsequent losses. Pigments containing heavy metals such as lead absorb X-rays more than others and X-radiographs register the differences.


X-ray Fluorescence Spectroscopy (XRF)

Method of examination used to identify inorganic pigments through their elemental constituents.

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