Illustrated Glossary

Damage caused by mechanical action such as rubbing, scraping, or repeated handling, resulting in the thinning or loss of surface material. Abrasion often produces a dull, roughened appearance and may expose underlying layers or supports.

The gradual accumulation of materials on the surface of an object over time. This can include dust, dirt, soot, corrosion products, or other environmental deposits that adhere to a work of art or historic material. Accretions may obscure the original surface, alter the appearance, or contribute to long-term degradation if not carefully managed.

Adhesive residue refers to the remaining traces of glue, tape adhesive, mounting pastes, or other bonding materials left on the surface of an artwork or object after the original adhesive element has been removed or deteriorated. These residues can cause discoloration, staining, embrittlement, surface distortion, and long-term chemical or mechanical damage. In conservation, identifying the type of adhesive and safely reducing or removing its residue is essential to prevent further deterioration and restore visual integrity.

A network of cracks that forms in a painting over time as part of its natural ageing process. These fissures typically run through all layers, including the ground, paint, and varnish. Ageing cracks result from the slow, cumulative movement of the support—whether canvas, panel, or another substrate—responding to continuous, subtle fluctuations in temperature and relative humidity. As the support expands and contracts over the years, the more brittle paint and ground layers are unable to accommodate these dimensional changes, eventually developing a characteristic crackle pattern that reflects the painting’s material history and environmental exposure.

The component of a paint that acts as the agglutinant, holding pigment particles together and adhering them to the support. The binder forms the continuous, cohesive film that constitutes the paint layer once it dries or cures. Its chemical nature varies according to the painting technique—for example, drying oils in oil painting, animal glue or egg in tempera, or acrylic polymer emulsions in modern paints—giving each medium its characteristic handling properties, appearance, and long-term behavior.

A whitish or hazy appearance that forms in a paint or varnish layer as a result of microscopic defects—such as voids, granules, or fine fissures—that develop over time. These micro-irregularities scatter incident light, causing the affected area to appear lighter or more opaque than the surrounding surfaces. Blanching is often associated with ageing, environmental fluctuations, or localized changes in the optical properties of the coating.

The unwanted diffusion or migration of a colorant—such as dye, ink, or pigment—into adjacent areas of a work of art. Bleeding typically occurs when excess moisture, water, or certain solvents mobilize the colorant, allowing it to travel beyond its original boundaries. This alteration can blur edges, change tonal values, and compromise the visual integrity or legibility of the object.

A raised protuberance on a surface, often bubble-shaped, resulting from the separation of an applied layer—such as paint, varnish, or adhesive—from its underlying substrate. Blisters commonly form due to factors like moisture, heat, chemical reactions, or mechanical stress, and they can compromise both the appearance and stability of the affected material.

A superficial cloudy or dull area that forms within a varnish layer. Blooming is most commonly caused by the deposition of atmospheric pollutants—such as ammonium sulfate—or by condensed moisture trapped in or on the varnish, often resulting from application under humid conditions. These factors alter the varnish’s optical properties, producing a whitish or hazy appearance on the surface.

Undulations, waves, or bulges that appear in a material—such as canvas or paper—that is intended to remain flat. Buckling typically results from uneven tension, fluctuations in humidity, or dimensional changes in the support or mounting materials.Buckling affects an area creating waves in a gradual, continuous way

Localized protrusions on a surface caused by pressure or deformation originating from within or beneath the material. Bulges may result from trapped moisture, structural distortions, detached layers, or the expansion of underlying components. Unlike buckling, which creates waves across a larger area, bulges form isolated bumps.

The powdering or friability of a paint surface caused by the deterioration or failure of the binding medium. As the binder breaks down—often due to weathering, ultraviolet exposure, or ageing—the pigment particles lose cohesion and are easily brushed or rubbed off, giving the surface a dusty or chalky appearance.

A small, thin fragment that breaks away from a surface as a result of external force, impact, or localized mechanical stress. Chips often expose the underlying material, creating sharp-edged losses that interrupt the original surface. They may occur in paint layers, plaster, ceramics, wood, and other brittle or rigid materials, and can be early indicators of structural weakness or damage from handling, accidental knocks, or environmental conditions.

A separation or loss of adhesion between layers in a stratigraphic structure—such as between paint layers, between paint and ground, or between the ground and the support. Cleavage occurs when materials fail, become incompatible, or respond differently to environmental changes. It can manifest as lifting, tenting, or flaking and, if left untreated, may lead to further paint loss or structural instability.

A broad, uneven wrinkling of a material, such as paper or canvas, without sharp creases or folds. Cockling typically occurs when moisture causes differential expansion or contraction across the surface, producing a textured, wavy appearance. Do not confuse cockling and buckling: cockling refers to fine, irregular wrinkles, whereas buckling describes broad, continuous waves.

The process of stabilizing degraded, weakened, or friable areas of a material by introducing or applying substances that bind and hold them together. Consolidation strengthens fragile surfaces—such as flaking paint, powdering pigments, or deteriorated paper—without altering the original appearance, ensuring both structural stability and long-term preservation.

Localized distortions in a canvas painting in which the corners pull inward toward the center of the artwork. Corner draws are usually caused by uneven tension during stretching, changes in relative humidity, or shrinkage of the canvas or ground layers.

The deterioration of metals or metal-containing materials caused by chemical or electrochemical reactions with their environment. In art conservation, corrosion typically results from exposure to moisture, pollutants, salts, or other reactive agents, leading to surface alteration, loss of material, or the formation of corrosion products that may affect the object’s stability or appearance.

The formation of fractures or fissures in a material caused by internal or external stresses. In art conservation, cracking may result from aging, environmental fluctuations, mechanical forces, or inherent material weaknesses, and can affect both the stability and appearance of an object.

A network of small cracks or fine fracture lines that forms in a paint layer, varnish, or glaze. In art conservation, crackle may result from aging, drying stresses, environmental fluctuations, or incompatibilities between layers, and can affect both the appearance and structural stability of the surface.

Microscopic fissures that develop in the surface of a hardened or dried material, typically as a result of aging, environmental fluctuations, or internal stresses. In a varnish layer, crazing can alter light refraction and produce a hazy or opaque appearance.do not confuse with Blooming or Blanching, Crazing is a physical cracking (visible network of micro-cracks), Blooming is a optical effect from moisture or disruption, not cracks.

A line, ridge, or visible mark formed in a flexible material as a result of folding, bending, or wrinkling, whether accidental or intentional. In conservation, creases may weaken the material along the fold and can be associated with distortion, fiber breakage, or surface abrasion.

A condition in which aged or weakened paint begins to lift and curl along crack edges, creating small concave or cup-shaped deformations in the paint layer. Cupping often indicates loss of adhesion and can progress to flaking or paint loss if not stabilized.

A series of regularly spaced scalloped or wave-like distortions visible along the edges of a canvas painting. Cusping is typically caused by the original stretching of the canvas over a stretcher or strainer, where tension is applied unevenly between tacking points. These distortions are often considered inherent to the painting’s original preparation rather than later damage, although changes in humidity, re-stretching, or lining can make them more pronounced or alter their appearance.

A straight, deliberate or accidental separation in a support caused by a sharp slicing action. In conservation, cuts may compromise structural integrity and often require stabilization or mending to prevent further damage.

The process of reducing or neutralizing the acid content of an artwork or artistic object, typically through the application of alkaline agents. Deacidification not only neutralizes existing acids but also deposits an alkaline reserve (buffer) to counteract future acid formation and slow long-term deterioration.

Changes or alterations in the overall form, plane, or dimensions of an object caused by internal or external stresses or forces. In conservation, deformations may include warping, buckling, dents, distortions, or shifts in alignment, and can affect both structural stability and visual appearance.

Similar to cleavage. The separation of a paint layer into its constituent strata, often caused by aging, environmental fluctuations, or loss of adhesion between layers. Delamination can lead to flaking, loss of material, and instability of the painted surface.

A localized impression, hollow, or depression formed on the surface of an object as a result of applied pressure or impact. Dents typically deform the material without breaking it, creating a displacement of fibers or substrate layers rather than a full rupture. In art conservation, dents may appear in paper, canvas, wooden panels, metal objects, or frames, and can be caused by handling, storage pressure, accidental impacts, or contact with protruding objects. Depending on the material and severity, dents may be reversible through controlled humidification, reshaping, or other conservation treatments.

A small, localized depression or indentation on a surface, typically shallow and rounded in form. Dimples may occur in a variety of materials—such as paper, canvas, wood, metal, or coatings—and can result from pressure, impact, manufacturing irregularities, or inherent material characteristics. In art conservation, dimples are usually minor distortions but may disrupt surface gloss, texture, or the visual continuity of an artwork. Treatment options vary depending on the substrate and may include controlled humidification, gentle reshaping, or surface consolidation when associated with more complex structural issues.

An unwanted alteration or shift in the original color of an object or material, typically resulting from aging, light exposure, pollutants, chemical reactions, or previous treatments. Discoloration may appear as darkening, yellowing, fading, or localized staining, and often affects both the aesthetic appearance and the interpretation of an artwork. In some cases, discoloration is irreversible, although some forms—such as surface staining or certain oxidation products—can be reduced through carefully controlled conservation treatments. Understanding the cause and extent of discoloration is essential for determining appropriate intervention and long-term preventive measures.

A turned-down corner of a sheet of paper or document, typically resulting from careless handling or the habitual marking of pages. Dog-ears may weaken the paper fibers and encourage further tearing or creasing.

Cracks that form during the natural drying or curing of paint layers, when upper layers shrink more rapidly than those beneath them. This tension produces raised ridges and exposed underlayers, often in a pattern resembling alligator skin, and indicates incompatibility or poor drying conditions

Loose, fine particles that accumulate on the surface of an artwork from the surrounding environment. Dust can attract moisture or pollutants, become embedded in porous materials, and contribute to long-term soiling if not safely removed.

A condition in which a material loses flexibility and becomes rigid, fragile, and prone to snapping, tearing, or powdering. Embrittlement results from aging, oxidation, acidity, or environmental stress and poses significant handling risks.

The temporary application of a protective tissue, adhered with a reversible adhesive, to stabilize fragile surfaces—such as flaking paint or delicate paper—during conservation treatment, transport, or structural repair.

A pigment or dye known to be unstable or light-sensitive, leading to fading or chromatic alteration when exposed to light, heat, or environmental stress. Fugitive colors compromise long-term appearance and require light-level precautions.

A material used to reintegrate areas of loss—such as gaps, cracks, abrasions, or missing sections—before surface finishing or inpainting. Fillers are chosen for compatibility, reversibility, and stability within the conservation process.

The controlled application and shaping of a filler material used to reconstruct losses, reestablish surface continuity, and prepare an area for retouching or further conservation treatment.

Severe instability in which paint or ground layers lift, curl, or detach from the support, often due to cleavage, cracking, or environmental fluctuations. Flaking poses an immediate risk of material loss and requires urgent stabilization.

A section of a flexible material bent onto itself, forming a ridge or crease. Folds may weaken fibers, distort imagery or text, and become permanent if not properly relaxed or treated.

Rust-colored or brownish spots that appear on aged paper due to oxidation of embedded metallic impurities, often encouraged by humidity and fungal activity. Foxing affects both appearance and long-term stability.

Fine, powdery debris or excrement left by wood-boring insects as they tunnel through materials. Frass is a diagnostic sign of active or past infestation and often accompanies structural damage.

A treatment using controlled gaseous agents to eliminate insects, mold, or other biological threats. Fumigation aims to arrest active infestations and prevent further damage while minimizing impact on the object.

See Mold

Accumulated dirt, skin oils, soot, and environmental pollutants deposited on or embedded within an artwork’s surface over time. Grime can obscure details, alter color, and interact chemically with underlying materials.

A preparatory layer—such as gesso, priming, or undercoat—applied to a support (canvas, panel, paper) to create a uniform, receptive surface for painting. The ground influences adhesion, texture, and long-term stability of the paint layers.

The presence and activity of biological agents—such as insects, larvae, microorganisms, or fungus—actively damaging or occupying an object. Infestations can cause structural loss, staining, and deterioration, and require prompt intervention

A conservation technique in which losses in a painting, drawing, or decorated surface are visually reintegrated using carefully matched, reversible materials. The purpose of inpainting is to restore design continuity without covering or altering any original paint, ensuring visual harmony while maintaining ethical standards.

Deterioration resulting from infestation by insects such as termites, beetles, moths, or silverfish. Damage may include holes, tunneling, frass deposits, weakened structures, and surface loss, often requiring both treatment of the infestation and repair of affected areas.

A condition in which a component of an artwork—such as paint, ground, or support—has lost stability and is actively failing or at risk of detaching. Insecure elements indicate weakened structure, compromised adhesion, or ongoing deterioration requiring prompt stabilization.

A small, triangular wedge inserted into the corner slots of a stretcher to expand the joints and increase tension on a canvas. Keys allow fine adjustment of the stretcher’s dimensions, helping maintain even tautness across the painting over time.

An area where paint, ground, or decorative surface is missing, exposing the underlying layer or support. Lacunae disrupt visual continuity and often require filling and inpainting to restore aesthetic coherence.

A form of delamination in which paint, ground, or other surface material detaches and rises away from the underlying layer, creating raised edges or air pockets. Lifting poses a high risk of loss and often requires immediate consolidation.

A structural conservation method used to reinforce weakened or brittle canvas paintings by adhering a secondary fabric to the reverse. Lining compensates for loss of strength in the original support and helps stabilize tears, deformations, and overall fragility.

The process of replacing or filling in missing material in a work of art or object to restore visual continuity and structural integrity. Loss compensation may involve inpainting, filling, or reconstructing areas that have been lost due to damage, deterioration, or wear, while ensuring compatibility with the original materials.

Missing portions of one or more layers of an artwork—such as paint, ground, or support—typically resulting from flaking, tearing, abrasion, insect activity, or mechanical damage. Losses affect both structural integrity and visual coherence.

A darkened, discolored band that forms around the edges of artworks on paper due to prolonged contact with acidic mat board or backing materials. Mat stains indicate acid migration and often accompany overall yellowing or embrittlement.

The act of repairing tears, splits, or cuts in paper, textiles, or other flexible supports by reattaching fibers, bridging gaps, or reinforcing weakened areas. Mending restores structural integrity and minimizes visual disruption.

Fungal growths that develop on organic materials when moisture, warmth, and poor air circulation are present. Mold feeds on the substrate, causing staining, weakening, and decay, and poses health risks that require careful remediation.

Paint applied at a later date over the original surface of an artwork, usually to mask damage, losses, or previous restorations. Overpaint is not part of the artist’s original intent and often ages differently, becoming visually discordant or obscuring original details over time.

Changes made by the artist during the creation of a work, such as repositioned figures or altered compositional elements, that remain beneath the visible surface. These earlier decisions may become visible over time as paint layers age, wear, or become more transparent.

A penetrating hole or perforation created by an impact from a pointed or forceful object. Punctures disrupt the support structure and often include associated tears, distortions, or compression of surrounding material.

See Inpainting

Linear abrasions caused by contact with a sharp or rough object, resulting in surface loss that may penetrate the paint, ground, or varnish layers. Scratches alter texture, continuity, and reflectance of the surface.

Dimensional reduction of a material caused by loss of moisture, heat exposure, aging, or chemical change. Shrinkage can produce tension, warping, cracking, and distortion in supports or surface layers.

The accumulation or deposition of particulate matter—such as dust, soot, grease, fingerprints, or airborne pollutants—on the surface of an artwork. Soiling dulls appearance, alters color, and may combine with moisture to form more tenacious grime.
See also: Grime.

Circular or radiating cracks that originate at a single point of impact and spread outward in a pattern resembling a spider web. Spiral cracks indicate localized trauma and may extend through multiple layers of the artwork.

A rupture occurring along the grain of wood or at the joint between two originally connected panels, usually caused by stress, shrinkage, or environmental fluctuations. Splits weaken structural integrity and may require reinforcement or realignment.

A discolored or blemished area caused by the absorption or penetration of foreign substances—such as water, oils, adhesives, or dyes—into the surface or structure of an artwork. Stains may be permanent or partially reducible through treatment.

The conservation process of diminishing or removing discolorations, tidelines, or intrusive blemishes—most commonly in paper supports—through controlled chemical or aqueous methods while preserving original material.

A rigid wooden framework used to support a canvas that lacks expandable corners, meaning its dimensions remain fixed. Unlike stretchers, strainers cannot be keyed out and therefore offer limited adjustability over time.

A wooden framework designed to support a canvas while allowing adjustment of tension through expandable, keyable corners. Stretchers ensure long-term tautness of the canvas and reduce strain on the painted surface.

Lines, ridges, or cracks appearing in the ground and paint layers of a painting where the canvas rests against the inner edges of a stretcher or crossbar. These marks result from insufficient tension or canvas movement over the support members.

A conservation treatment in which narrow strips of fabric are adhered along the edges of a canvas painting to reinforce weakened or damaged tacking margins. The added strips provide additional strength and support, allowing the painting to be safely re-stretched without placing stress on the original canvas.

In art conservation, strip lining is considered a minimally interventive alternative to full lining, as it preserves the original canvas while improving structural stability and reducing the risk of further tears or distortion at the edges.

The underlying material that forms the physical foundation of an artwork—such as canvas, panel, paper, metal, stone, or composite board. The support’s characteristics strongly influence the artwork’s stability, appearance, and conservation needs.

The margin of canvas or fabric used to secure the artwork to its auxiliary support, typically by nails, staples, or tacks. Tacking edges bear mechanical stress and are often the first areas to show wear, distortion, or tears.

A break or separation in paper, fabric, or another flexible support caused by excessive tension, impact, or handling. Tears compromise structural strength and frequently require mending or reinforcement.

A visible line or boundary left on a surface—most commonly on paper—where water or another liquid has dried unevenly. As the liquid migrates and evaporates, it carries soluble materials such as dirt, degradation products, or discoloration to the edge, where they become concentrated and form a distinct line.

A protective, transparent coating composed of resin dissolved in a volatile solvent, applied to the surface of a painting to enhance saturation, modify gloss, and safeguard against dirt and abrasion. Over time varnish may discolor and require removal or replacement.

Distortion or bending of a support—such as canvas, panel, or paper—that should remain flat, caused by uneven moisture absorption, heat exposure, or internal stresses. Warping can affect paint layers and overall structural stability.

Deterioration caused by exposure to water or high moisture, resulting in staining, swelling, planar distortion, mold growth, bleeding of media, or weakening of structural components. Water damage often requires immediate intervention to prevent ongoing deterioration.