• About This Glossary

• à grain

• abrasion

• absorbent ground

• additive

• aqueous lining

• atmospheric perspective

• backing board

• basket weave

• basse

• binder

• binding medium

• blocking in

• bolt

• bolt match

• BSE (backscattered electron)

• canvas

• canvas stamp

• chain lines

• cleavage

• color merchant

• commercially primed

• consolidant

• consolidate

• Conté crayon

• cradle

• craquelure

• cross section

• cross-sectional analysis

• crossbar

• crosshatching

• cusping

• darkfield illumination

• deckle edge

• delamination

• DIC

• double thread fault

• drier

• drying cracks

• edge-lining

• electron microprobe analysis (EMPA)

• en plein air

• extender

• facing

• false-color infrared

• field easel

• figure

• filler

• fluorescence

• foldover

• foxing

• FTIR (Fourier transform infrared microspectroscopy)

• furnish

• glaze

• glue-paste lining

• graphite

• ground

• hardboard

• haute

• horizon line

• hyperspectral

• ICA spring stretcher

• impasto

• infrared reflectogram

• infrared reflectography

• inpainting

• interleaf

• IRR

• Japanese paper

• keying out

• keys

• laid paper

• lake pigment

• lay-in

• laying in

• lead soap formation

• linear perspective

• lining

• lisse

• marine

• mat burn

• metal soap formation

• miter

• modeling

• mortise and tenon joint

• mount

• mounting

• natural-resin varnish

• oil

• orthogonals

• overpaint

• palette

• palette knife

• panel

• paysage

• peinture claire

• pentimento (plural: pentimenti)

• perspective

• photomicrograph

• pigment

• plain weave

• plein air

• PLM (polarized light microscopy)

• pre-primed

• preparatory layer

• primary cusping

• priming

• radio opaque

• radio transparent

• raking light

• Raman microspectroscopy

• rebate

• relining

• reserve

• retouching

• scumble

• secondary cusping

• SEM/EDX (scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy)

• semiglaze

• SERS (surface-enhanced Raman spectroscopy)

• size

• sizing

• skinning

• specular light examination

• standard-format supports

• stereomicroscopic examination

• strainer

• stretcher

• stretcher-bar cracks

• stump

• stumping

• substrate

• support

• surface dry

• synthetic varnish

• tacking edge

• tacking margin

• tangential

• tapping out

• taquets bois

• thread count

• thread-angle map

• thread-count match

• thread-density map

• traction cracks

• transmitted-infrared imaging

• transmitted-light imaging

• twill weave

• ultraviolet radiation

• underdrawing

• underpainting

• UV (ultraviolet)

• UV fluorescence

• vanishing point

• varnish

• warp thread

• warp-angle map

• warp-thread match

• warp-thread repair

• wash

• watermark

• wax-resin lining

• weave

• weave match

• weft thread

• weft snake

• weft-angle map

• wet-in-wet

• wet-on-wet

• wet-over-dry

• wove paper

• X-radiography

• X-ray

• XRF (X-ray fluorescence spectroscopy)

• About This Glossary

  • Several sources were particularly helpful in compiling this glossary: American Institute for Conservation of Historic and Artistic Works, Painting Conservation Catalog, vol. 2, Stretchers and Strainers (Paintings Specialty Group of the AIC, 2008); David Bomford, Jo Kirby, John Leighton, and Ashok Roy, Art in the Making: Impressionism, exh. cat. (National Gallery, London/Yale University Press, 1990); Anthea Callen, The Art of Impressionism: Painting Technique and the Making of Modernity (Yale University Press, 2000); Anthea Callen, Techniques of the Impressionists (New Burlington Books, 1982); Canadian Conservation Institute, Condition Reporting: Paintings, pt. 3, Glossary of Terms (Government of Canada, 1994), https://www.cci-icc.gc.ca/resources-ressources/ccinotesicc/10-11-eng.aspx; Anne F. Clapp, Curatorial Care of Works of Art on Paper (Lyons & Bueford, 1987); Francis W. Dolloff and Roy L. Perkinson, How to Care for Works of Art on Paper (Museum of Fine Arts, Boston, 1985); E. J. Labarre, Dictionary and Encyclopedia of Paper and Paper-Making, 2nd ed. (Swets & Zeitlinger, 1952); Ralph Mayer, The Artist’s Handbook of Materials and Techniques (Viking, 1982); Knut Nicolaus, The Restoration of Paintings (Könemann, 1999); Iris Schaefer, Caroline von Saint-George, and Katja Lewerentz, Painting Light: The Hidden Techniques of the Impressionists (Skira, 2008); Silvie Turner, The Book of Fine Paper (Thames & Hudson, 1998); and James Watrous, The Craft of Old-Master Drawings (University of Wisconsin Press, 1957).

• à grain

  • By the late nineteenth century, commercially primed canvas—whether purchased ready-stretched or by the roll—was available in two principal thicknesses of ground application: à grain, indicating a single layer of ground; and lisse, indicating two layers. À grain preparations retain more of the canvas texture than lisse applications.

• abrasion

  • The removal of original paint from the surface of the artwork. When mentioned in condition summaries and previous conservation treatments, abrasion often refers to damage incurred through previous cleaning (with solvents or water) or physical contact with the paint surface. Abrasion by wiping or scraping back paint with a palette knife can also be part of the artist’s technique.

• absorbent ground

  • A type of ground particularly popular in the second half of the nineteenth century that, often due to its composition, absorbed some of the medium from oil paints, resulting in a faster-drying, matte surface. Although the composition of absorbent grounds varied greatly, many used large proportions of chalk and an aqueous binder such as glue as part of the mixture. See also ground.

• additive

  • Materials added to paint other than pigments and binders. These can include extenders and materials such as wax or resins, which may function to stabilize the paint or improve its working properties.

• aqueous lining

  • A lining process that uses an aqueous, or waterborne, adhesive such as glue, paste, or a glue-paste mixture. See also lining.

• atmospheric perspective

  • A method of creating the illusion of depth by decreasing the color contrast and strength of borders, and by rendering colors cooler or bluer for objects in the distance, as if by an intervening atmosphere. Also called aerial perspective. See also perspective.

• backing board

  • Boards—currently made from foamcore or Coroplast, but in the past made from hardboard, cardboard and Masonite—attached to the verso of a painting to provide a buffer for fluctuating temperature and humidity and protection from grime and contact. These can be attached directly to the verso of the stretcher or held in place via pressure from the framing hardware.

• basket weave

  • A weave in which multiple weft threads are woven into multiple warp threads. A double weave is referred to as a two-by-two basket weave. When thicker threads are used, the basket weave can accentuate the checkerboard weave pattern.

• basse

  • See standard-format supports.

• binder

  • The material used to hold various solid, particulate components, including pigments and extenders, of paint together and which additionally serves to bind the solids together upon drying and adhere the paint material to the support. Often this material is a liquid, either naturally, as with oils, or when dissolved in water, as with gum arabic, the medium in watercolors. Also called binding medium.

• binding medium

  • See binder.

• blocking in

  • See laying in.

• bolt

  • The length of fabric, usually between 100 and 200 m in canvas preparation, created by a single length of warp threads on a loom. Bolts were further divided into rolls, which were individually sized and prepared for distribution to color merchants.

• bolt match

  • See weave match.

• BSE (backscattered electron)

  • See SEM/EDX (scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy).

• canvas

  • Textile—usually composed of linen, cotton, hemp, or jute, or combinations of these—used as a primary support for painting and traditionally as a secondary support for pastel or chalk drawings on paper.

• canvas stamp

  • See color merchant.

• chain lines

  • Widely spaced lines formed in paper made on a laid mold screen, most clearly seen when light is transmitted through the paper sheet. See also laid paper.

• cleavage

  • A condition in which one or more of the layers of an artwork—including varnish, paint, and ground layers—are in the process of separating from the support or from each other. Causes of cleavage include shrinkage of the support and poor adhesion between or within layers.

• color merchant

  • Shop selling artists’ materials, including pigments, easels, palettes, oil paints, watercolors, drawing instruments, and supports. These became increasingly common in nineteenth-century Paris and sometimes provided additional services such as framing and restoration. In some cases, supports prepared by a color merchant bear a corresponding stamp on the support verso or stretcher. Also called colormen or marchands de couleur.

• commercially primed

  • Supports, such as canvas, that are industrially prepared and primed in large batches. In canvas preparation, the result is a roll of pre-primed canvas that is often cut down, either by the artist or a color merchant, and individually stretched.

• consolidant

  • Liquid material, usually solvent- or waterborne, used in conservation treatments to readhere lifting, broken, or flaking materials to the support.

• consolidate

  • See consolidant.

• Conté crayon

  • Fabricated drawing sticks. Although originally manufactured from powdered graphite, these crayons would later be comprised of pigments and clay to substitute natural black, red, and white chalks; depending on their manufacture they can produce powdery to slightly greasy characteristics.

• cradle

  • A series of interwoven wooden strips applied in a grid pattern used to reinforce a solid support such as a wooden panel or hardboard.

• craquelure

  • Network of cracks.

• cross section

  • See cross-sectional analysis.

• cross-sectional analysis

  • In this technique, a microscopic sample—including any combination of ground, paint, and surface layers—is taken, usually from the edge of a painting or an area of paint loss, and mounted in a transparent resin. The resin block, once hardened, is ground and polished, exposing all the constituent layers of the sample in one plane. Cross sections can be observed and documented with a microscope in reflected light and ultraviolet fluorescence; they can also be subjected to analysis with SEM/EDX, FTIR, and Raman microspectroscopy.

• crossbar

  • An additional vertical or horizontal bar that functions to support the main stretcher or strainer members. Also called cross brace.

• crosshatching

  • A technique in both painting and drawing in which volume or texture is created by two sets of strokes of varying interval and thickness, usually close to perpendicular to one another, that create a kind of X shape.

• cusping

  • The pattern created along the edges of a stretched textile where the weave distorts in reaction to stretching and the attachment to a secondary support, such as a stretcher. Also called scalloping.

• darkfield illumination

  • An optical microscopy technique used for the examination of opaque samples, such as paint cross sections. The sample is illuminated from above through the objective and the light is reflected off of the sample that is placed against a dark background.

• deckle edge

  • An irregular (wavy or feathered) edge that is typically formed on all four sides of a handmade sheet of paper where pulp has seeped under the inner edge of the paper mold’s removable wooden frame (deckle) during formation; the deckle fits over the mold to contain the paper pulp as it drains through the screen surface.

• delamination

  • The separation of components of an artwork such as the original support from the lining.

• DIC

  • A technique of illuminating and imaging microscopic samples that shows phase differences in the sample in a relief-like fashion. When examining cross sections with reflected light microscopy, DIC enhances certain aspects of the sample and also masks certain types of imperfections, such as scratches due to the grinding and polishing process.

• double thread fault

  • A defect of hand weaving in which two warp threads are temporarily woven as a single thread.

• drier

  • A solution of metallic compounds added to paint mixtures to reduce drying time. Also called siccative.

• drying cracks

  • A condition of painted surfaces caused by uneven rates of drying between layers. Drying cracks can occur in the paint or varnish layers and tend to be wide with rounded edges. Also called traction cracks and shrinkage cracks.

• edge-lining

  • The reinforcing of the tacking margins of a canvas painting by local lining along the edges of the support with a secondary fabric. Also called strip lining.

• electron microprobe analysis (EMPA)

  • A scientific method of analysis used to determine the composition of small volumes of samples. The instrument uses an electron beam to generate X-rays characteristic of the elements in a few cubic micrometers (μm) of a sample (1 μm = 1/25,400 of an inch). This technique is able to give accurate quantitative analysis of the concentration of specific elements in an artist’s materials, even for small concentrations and for the analysis of lighter elements, such as sodium, aluminum, and silicon, that can be found, for example, in the pigment ultramarine blue.

• en plein air

  • See plein air.

• extender

  • Inert additives, such as calcium carbonate (chalk) and calcium sulfate (gypsum), to paint intended to give bulk to the pigment. Kaolin (hydrated aluminum silicate or China clay) is often used as an extender in chalks, crayons, and pencils.

• facing

  • The act of applying paper material, often Japanese tissue, to part or all of an artwork to facilitate treatment or protect endangered paint layers. Often paintings were faced with tissue and wheat starch paste to stabilize the paint layer during the lining process. If this layer was not diligently removed after lining or consolidation, facing residues remain that can present aesthetic and structural problems over time.

• false-color infrared

  • Unlike a true-color image, a false-color image depicts objects with colors arbitrarily assigned based on the sensitivity of specific materials at certain energies in the spectrum. A false-color image is created by combining information from three individual images input into each of the red, green, and blue (RGB) channels of a color image and enables detection of specific features that are not otherwise apparent. False-color imaging usually relies on at least partial information from outside the visible spectral range (300–700 nm), such as infrared. As opposed to a normal, grayscale infrared image taken with a broadband filter (each covering approximately 200–300 nm), the false-color infrared images created in this study combine information from different spectral bands captured with a hyperspectral camera, which simultaneously acquires a number of images from 960–1730 nm in narrow, 3.4-nm-wide bands. The specific bands assigned to each channel are chosen so that their combination in the resulting false-color infrared image allows the greatest legibility of the features in question.

• field easel

  • A portable easel designed for plein air, or outdoor, use. A field easel was usually small to medium-sized and had telescopic or collapsible legs based on a tripod design (three vertical legs joined at one end), often with a horizontal cross brace for stability, and a small ledge and sliding head that held the canvas or board support. Such easels were also available with an independent vertical element intended to support an umbrella, or as box easels, which incorporated a storage compartment for the artist’s materials.

• figure

  • See standard-format supports.

• filler

  • See extender.

• fluorescence

  • Emission of light by an object or material when exposed to UV radiation.

• foldover

  • The crease made in a canvas where it is folded over stretcher or strainer bars. The original foldover corresponds to the first stretching of the canvas. If a canvas is mounted onto a new stretcher of slightly different dimensions, a new foldover is created. Also called turnover.

• foxing

  • Typically the chemical action of mold on metallic salts present in paper that develops with elevated humidity and temperature to produce small spots of decomposition, visible as reddish-brown discoloration.

• FTIR (Fourier transform infrared microspectroscopy)

  • This extremely versatile technique allows researchers to characterize a vast array of materials, such as pigments, fillers, binders, and varnishes. Scientists compress a few microscopic particles of a sample into a thin film, place it under a microscope, and record a graph—called a spectrum—that shows peaks at the discrete frequencies at which the sample absorbs the incoming infrared radiation. By comparing this spectrum with a reference database, scientists can identify an unknown material.

• furnish

  • The materials from which paper is manufactured. This term can be used to describe the type of plant fiber used in the raw stock (such as wood pulp and rag) as well as the general composition or combination of materials.

• glaze

  • A transparent or translucent paint layer, usually highly saturated and incorporating extra medium. Traditionally, glazes were used to add volume to form or to change the value and hue of a particular area.

• glue-paste lining

  • See aqueous lining.

• graphite

  • An allotropic form of pure carbon used by artists unprocessed as a stick or lump set into a port crayon (metal holder) or compressed into thin rods and encased in wood-cased pencils. In 1795 a substitute for natural and pure carbon, the fabricated graphite pencil, was invented in France. It consists of finely powdered graphite mixed with clay and water and fired at a high temperature. The ratio of clay to graphite determines the hardness or softness of fabricated graphite pencils. Soft pencils require very little pressure to lay down significant amounts of graphite on the surface, creating broad, dark lines, while hard pencils deposit less graphite on the surface and create fine, silvery lines.

• ground

  • An opaque layer applied to the canvas, usually over a sizing layer, to prepare the canvas to receive paint. Thinner grounds, including à grain, leave more of the canvas texture apparent, while thicker grounds, including the double-layer lisse, mute the canvas texture. Grounds in the nineteenth century were commercially available in white and a variety of pale colors, and in both absorbent and nonabsorbent consistencies. Also called priming or preparatory layer(s).

• hardboard

  • A solid support made from pressed wood fibers.

• haute

  • See standard-format supports.

• horizon line

  • A line that denotes the boundary between the sky and the ground. The horizon is also an indication of the viewer’s eye level.

• hyperspectral

  • Hyperspectral imaging collects a series of imagesfrom 960 to 1730 nm in narrow, 3.4-nm-wide bands. Many materials absorb and therefore have what is called a spectral signature at a specific wavelength. Hyperspectral images can therefore help identify specific materials, such as pigments, based on this signature. They can also be combined in various ways to form false-color images.

• ICA spring stretcher

  • The Intermuseum Conservation Association (ICA) spring stretcher, designed by Richard Buck in 1950, is the most common type of spring-tension stretcher. It is constructed with spring-loaded corners intended to exert continuous, even tension on the canvas as it changes in response to fluctuations in humidity. The stretcher was available, under the name Superior Spring-Stretcher, until 2001.

• impasto

  • Thick, textural application of paint.

• infrared reflectogram

  • See infrared reflectography.

• infrared reflectography

  • This technique exploits the varied transmission, absorption, and reflection properties of infrared radiation by artists’ materials. The degree of penetration depends on the thickness of the paint, the pigments used, and the wavelength of the infrared radiation. Many paints appear partially or completely transparent, while others, such as black, absorb the infrared radiation and appear dark. An infrared-sensitive camera captures the light reflecting off the surface of the painting. The resulting image is known as an infrared reflectogram. Infrared reflectography is used to distinguish pigments, inscriptions, underdrawings (particularly those done in carbon-rich materials such as charcoal and pencil over a white or light-colored ground), and changes in a composition not visible to the naked eye.

• inpainting

  • Painting done by a conservator to restore areas of loss or damage in an original paint layer. Inpainting is limited to the area of loss and is carried out in a medium that remains readily distinguishable from the original, does not discolor, and can be easily removed in the future.

• interleaf

  • Material between the layers of a lining, usually a secondary, inert fabric or a solid support such as hardboard.

• IRR

  • See infrared reflectography.

• Japanese paper

  • Typically handmade paper composed of the inner bark of the gampi, mitsumata, or mulberry plants. Although these papers do not contain a watermark, they often reveal faint mold impressions from the bamboo screens on which the paper sheets were made.

• keying out

  • The act of tapping the keys to expand the stretcher and increase tension on a canvas support. See also keys.

• keys

  • Small wedges, often roughly triangular in shape, inserted into the joints of a stretcher to allow the stretcher to be expanded and tension on the canvas increased. This process is called keying out or tapping out.

• laid paper

  • A type of handmade or machine-made paper formed on a mold screen of closely spaced, parallel wires (laid lines) that are secured in place by widely spaced wires (chain lines) woven around the laid lines. When the paper mold is dipped into water containing a fine dispersion of paper fibers, the fibers settle selectively along the wires as the water drains off; the formed sheet bears the laid wire screen pattern that is most clearly seen when light is transmitted through the paper sheet. Handmade papers prior to the last quarter of the eighteenth century were formed on a single laid and chain screen secured along the chain lines to the wooden ribs of the mold. When the mold was lifted from the pulp to form the sheet, a slight vacuum was created by the ribs, causing thicker pulp formation along the chain lines, which appeared as shadows in the finished sheet. These shadows are characteristic of paper formed on a single screen (or single-faced mold); such sheets are sometimes referred to as antique laid paper. When a second set of wires is added between the screen and the ribs of the mold, suction along the chain lines is prevented, thus eliminating the shadows. Paper made on these double-faced molds, as they are known, is sometimes referred to as modern laid paper.

• lake pigment

  • A translucent pigment made by precipitating a dye onto an inert substrate. Common lake pigments in the nineteenth century include madder and carmine (cochineal).

• lay-in

  • See laying in.

• laying in

  • The act of establishing either the major elements of a work in solid paint or the initial paint layers. The lay-in is a form of underpainting, also referred to as the ébauche or block-in.

• lead soap formation

  • A condition in which lead compounds form when lead in pigments or driers in the paint or ground layers reacts with fatty acids in the oil or varnish. Frequently these lead soaps form aggregates that can move toward the surface of a work, appearing as small, sometimes white protrusions or bumps. These protrusions can sometimes cause cracks, losses, and destabilization of the paint layer(s) over time.

• linear perspective

  • A technique of creating the illusion of three-dimensional space on a flat surface such that the relative scale, shape, and location of an object are guided by a series of parallel lines called orthogonals (imagined or drawn) that converge as they recede, meeting at a distant point on the horizon, called a vanishing point. Two-point linear perspective refers to two different vanishing points, which can occur when the artist has incorporated two different viewpoints into the painting. Three-point perspective would incorporate a third vanishing point, usually above or below the horizon, as in buildings seen from above or below. See also orthogonals, perspective, vanishing points.

• lining

  • The act of structurally reinforcing the original canvas or paper support with a similar or like material to provide strength or reinforcement to the artwork. A painting can be lined with a second textile or canvas with an adhesive, typically aqueous materials, wax-resin mixtures, and Beva 371. Works of art on paper are traditionally lined with Japanese kozo (paper made of the inner bark fibers of the mulberry plant), adhered overall with prepared wheat starch paste.

• lisse

  • By the late nineteenth century, commercially primed canvas—whether purchased ready-stretched or by the roll—was available in two principal thicknesses of ground application: à grain, indicating a single layer of ground; and lisse, indicating two layers. A lisse (French for “smooth”) application fills the interstices of the canvas weave to a greater degree than à grain applications.

• marine

  • See standard-format supports.

• mat burn

  • Brown discoloration that develops over time in paper that is in direct contact with a mat manufactured with inferior materials, such as paper stock that contains wood pulp. Under certain atmospheric conditions, particularly with elevated humidity and temperature, acid from the window bevel of poor-quality mat board can migrate into the paper adjacent to it and cause oxidation of the cellulose.

• metal soap formation

• miter

  • A way of joining two abutting members such that both are carved at equal angles to create the desired angle of the joint. For example, in most frames and stretchers, both members would be cut at a 45 degree angle to make a 90 degree joint.

• modeling

  • In two-dimensional art forms (such as drawing or painting), modeling is the depiction of three-dimensional objects achieved through the representation of light and shadow.

• mortise and tenon joint

  • A type of joint made of two components: the tenon, or the projecting end of the member, and the mortise, or the slot into which the tenon fits on the receiving member. Variations include full mortise and tenon, in which both the front and back sections of the mortise are mitered, and half mortise and tenon, in which only the front part of the mortise is mitered and the back is a simple lap joint. Also called tongue and groove.

• mount

  • See mounting.

• mounting

  • Adhering a canvas painting to a rigid support such as a board. Also called marouflage.

• natural-resin varnish

  • A varnish layer made from the dissolved resin of natural origin, including plants, trees, or insects. Natural resins include damar and mastic. See also varnish.

• oil

  • In the present study, this term generally refers to drying oils used in artists’ paint, usually linseed oil but also poppy and walnut oils, among others. Drying oils form a film when exposed to air and cure over time.

• orthogonals

  • Lines drawn within the geometry of linear perspective to guide the scale and angular recession of objects and figures in space. Such lines extend into space perpendicular to the picture plane and represent parallel vectors.

• overpaint

  • Paint or restoration material applied over the artist’s original paint. Most often applied by another artist or a restorer at a later date, overpaint was used to cover damages and make aesthetic changes to the artwork. It is often excessive and is generally avoided in favor of localized inpainting.

• palette

  • Either the range of colors used by an artist for a particular work or the hard surface used by an artist to stage and mix colors.

• palette knife

  • A spatula-like tool used for mixing and applying paint and ground layers. Palette knives usually consist of a handle and a thin, flexible, blunt-tipped metal blade.

• panel

  • Traditional description for flat, wooden supports used for painting. The term can also refer to more modern supports such as hardboard and Masonite.

• paysage

  • See standard-format supports.

• peinture claire

  • A method of including opaque, pale, or white pigments in color mixtures. Also called blonde painting.

• pentimento (plural: pentimenti)

  • A compositional change made by the artist during an artwork’s execution.

• perspective

  • A technique of depicting volumes and spatial relationships on a flat surface. See also linear perspective, atmospheric perspective.

• photomicrograph

  • An image taken through a microscope.

• pigment

  • Colored particles used in artistic media such as oil paint, pastel, chalks, and watercolor.

• plain weave

  • Weave pattern where the weft threads are woven over every other warp thread. Also called tabby weave. 

• plein air

  • The act of painting or drawing outdoors. Also called en plein air.

• PLM (polarized light microscopy)

  • This technique uses a light microscope with two polarizing filters (one above and the other below the specimen) to characterize the optical and morphological properties of a specific material. A minute sample is mounted on a glass slide, dispersed in a transparent medium, and examined in transmitted light. The microscopist studies the color, shape, size, sample homogeneity, refractive index, and other optical phenomena of pigments and fibers and how they interact with light. These observations, when compared to a database of reference materials, allow an experienced analyst to determine the individual pigment or fiber material present in a sample.

• pre-primed

  • Indicates a canvas of large dimensions that was primed before being cut to size and mounted on a stretcher. The presence of ground extending to the edges of the canvas is indicative of pre-priming. Canvases were sometimes pre-primed by an artist or assistant, but, by the late nineteenth century, more commonly by commercial manufacturers who sold pre-primed canvas ready-stretched or in rolls for artists to stretch themselves.

• preparatory layer

  • See ground. 

• primary cusping

  • Strong cusping of a textile support that results from stretching before preparation—either by an artist or color merchant stretching an individual canvas before priming or as an effect of larger commercial or industrial preparation of a canvas. See also cusping.

• priming

  • See ground.

• radio opaque

  • A term used to describe materials of high atomic weight (for example, lead white paint), which block X-rays and appear light in X-ray images. See also X-radiography.

• radio transparent

  • A term used to describe materials of low atomic weight (for example, canvas), which are easily penetrated by X-rays and appear darker in X-ray images. See also X-radiography.

• raking light

  • Illumination from an oblique angle used to highlight the topographical features of an artwork.

• Raman microspectroscopy

  • With this noninvasive technique, scientists can quickly and easily identify a wide range of materials nondestructively. Using a microscope, spectra can be recorded from samples as small as 1 micron (one thousandth of a millimeter) across, and individual pigment particles can be analyzed, either as loose samples or on the surface of cross sections. Visible and invisible laser light is focused through a microscope, and the small portion of light that interacts with the material under study (a phenomenon known as the Raman effect) is scattered back into the microscope onto the detector. This scattered radiation is recorded as a function of wavelength and displayed as a spectrum, a graph in which each particular compound has a characteristic fingerprint. Complementary to FTIR, this technique can characterize both inorganic compounds (such as pigments, fillers, and minerals) and some organic compounds, although with organic substances it is sometimes impaired by the fluorescence of the materials under the laser.

• rebate

  • Small margin inside a frame against which a painting or work of art rests. Also called rabbet.

• relining

  • This term can refer to the lining of a painting and also to the act of removing a lining from a painting and lining it again.

• reserve

  • An area of a work of art left unfinished to be executed later. In practical terms, a figure may be left in reserve while the background of a work is built up, then completed afterward.

• retouching

  • This term is commonly used interchangeably with inpainting; however, it can also refer to overpaint or repaint, generally in reference to a conservator’s intervention. Retouching may also include toning of original paint that has been damaged or abraded. See also inpainting.

• scumble

  • An opaque paint layer applied so thinly it appears as a translucent veil over the preexisting layers. Sometimes a scumble is applied roughly or with a stiff-bristle brush that retains an uneven texture and thickness.

• secondary cusping

  • Cusping related to the stretching of a pre-primed canvas to a stretcher, usually by either a color merchant or the artist. See also cusping.

• SEM/EDX (scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy)

  • This technique utilizes electrons, rather than light, to create an image of a sample. It allows for the analysis of very small quantities of materials. The sample is coated with a thin film of carbon or gold, and a small beam of electrons is focused on the sample’s surface. Secondary electrons allow scientists to obtain a three-dimensional image at very high magnification and resolution (up to 100,000×); backscattered electrons (BSE) highlight the distribution of the elements, recording them in different shades of gray according to their atomic weight; and X-ray fluorescence emission allows analysts to determine which elements are present and to infer inorganic (mineral and synthetic) pigments and fillers. The EDX spectrum consists of a graph containing a series of peaks, each one occurring at a precise energy characteristic of a particular element. It is important to note that this technique gives information about what elements are present in a sample but not about their relationships to one another; it also does not indicate the organic compounds (such as binding medium) present. For these reasons, it is best complemented with polarized light microscopy or a molecular fingerprinting technique such as Raman microspectroscopy or FTIR.

• semiglaze

  • A translucent paint layer usually incorporating extra medium and both translucent and opaque pigments.

• SERS (surface-enhanced Raman spectroscopy)

  • A type of Raman microspectroscopy that requires specific preparation of the sample before analysis. Because of its extremely high sensitivity and its ability to quench fluorescence, it is particularly well-suited to the identification of natural organic colorants like those used to make lake pigments. A silver colloid, a suspension of silver nanoparticles obtained by chemical reduction of a silver salt (generally silver nitrate), is typically employed. Prior to analysis, the sample is exposed to hydrofluoric acid vapors in order to increase the absorption of the dye on the metal surface of the silver colloid, thus enhancing the SERS signal. After that, a small drop of the silver colloid is deposited onto the sample and analysis is carried out with a Raman microscope.

• size

  • See sizing.

• sizing

  • Material additives, commonly gelatin or glue, added to a support, such as wood, canvas, or paper, to seal it and reduce its ability to absorb paint and other media. In the preparation of canvas, hardboards, and panels, the size is applied before the ground layers. For paper, this material is incorporated internally in the pulp stage or applied to the surface of the formed paper during its manufacture to increase its resistance to water penetration (introduced by ink or watercolor). The process of applying the size layer is called sizing.

• skinning

  • Areas of paper where the fibers have been abraded, or “skinned,” from the surface. The term can also refer to the disruption of a paint surface due to abrasion or solvent action.

• specular light examination

  • Examination of an art object with the illumination angled directly in front of the work in order to maximize specular reflection, or reflection of the light, off the three-dimensional and glossy areas. Images taken under this condition can sometimes show artist changes not readily apparent with other kinds of illumination such as raking light.

• standard-format supports

  • The range of ready-made commercial supports—canvas, panel, paper, and card—available in an array of fixed sizes that are constant regardless of manufacturer. Standard-size supports are numbered from 1 to 120 and are available in three shapes: portrait (figure), landscape (paysage), and seascape (marine). These three formats have their longer dimension in common, with the short side becoming progressively shorter, so that the portrait format is the closest to being a square, the seascape the narrowest, and the landscape between the two. Some suppliers offered additional variations on select landscape and marine formats, further classifying them as haute (tall) and basse (short). The dimensions of these supports range from 12 to 130 by 22 to 195 cm.

• stereomicroscopic examination

  • Examination of an object with a stereomicroscope, which utilizes reflected light and is designed with two oculars, one corresponding to each eye, to give a three-dimensional visualization of the object at a magnified scale.

     

• strainer

  • A wooden framework with fixed corners used to mount textiles for painting. It is the secondary or auxiliary support for a canvas painting.

• stretcher

  • The wooden framework with expandable joints over which a canvas painting is stretched and attached. It is the secondary or auxiliary support for a canvas painting. Also called a chassis.

• stretcher-bar cracks

  • Cracks along the edges of the stretcher members, including the crossbars, from repeated contact between the canvas and stretcher over time.

• stump

  • See stumping.

• stumping

  • A drawing technique used to blend powdery media in which a piece of soft paper, felt, or leather, rolled to form a point (stump), is held at an angle and rubbed back across the paper surface to transfer the media.

• substrate

  • An inert substance, such as chalk, onto which dyes are precipitated. In the present study, the term is used with regard to lake pigments.

• support

  • The physical substrate of an artwork. Can include textiles, wood, and other types of board, metal, and paper.

• surface dry

  • A paint layer that is dry to the touch.

• synthetic varnish

  • A type of varnish introduced in the twentieth century that is comprised of a dissolved synthetic polymer. See also varnish.

• tacking edge

  • See tacking margin.

• tacking margin

  • The edges of the textile support that extend over the sides of the stretcher or strainer and by which the support is attached, often with tacks. Also called tacking edge.

• tangential

  • A longitudinal cut of wood made perpendicular to the rays and tangential to the annual growth rings. In a cut of this type, the annual rings appear as irregular, wavy patterns. Also called tangential section.

• tapping out

  • See keys.

• taquets bois

  • Small spacers used to transport paintings of the same size face to face while wet. A taquet bois usually consisted of a small wooden cylinder with metal points protruding from either side, almost like a two-sided pushpin. Such spacers are usually associated with plein air painting as they provided a method of transporting paintings between the outdoors and the studio without damaging the still-wet paint surface. Spacers could also have been utilized as a way to safely store paintings between painting campaigns.

• thread count

  • The number of threads per centimeter in the horizontal and vertical directions of a textile support, as determined by specially developed, automated software. Researchers from the Thread Count Automation Project—including Rick Johnson of Cornell University, Don Johnson of Rice University, and Robert Erdmann of the University of Arizona—use a program that precisely counts the threads in a canvas and maps variations in the weave density from an X-ray. The results can provide information about weaving and priming processes and can be used to identify canvases cut from the same fabric.

• thread-angle map

  • Heat map for the warp and weft threads generated by Thread Count Automation Project software that displays the angles of corresponding threads across the painting. These maps give indications about the weaving and preparation processes and mainly show cusping, both primary and secondary. In addition, weft-angle maps reveal weaving features such as weft snakes and warp-thread repairs.

• thread-count match

  • A statistical agreement between thread-count measurements among two or more canvases.

• thread-density map

  • Heat maps generated by Thread Count Automation Project software that illustrate the deviation of thread counts from the average thread count in the warp or weft direction across an entire painting. Patterns in thread-density maps can be used to determine whether paintings have canvas supports that came from the same bolt of fabric, or bolt matches.

• traction cracks

  • See drying cracks.

• transmitted-infrared imaging

  • This technique is similar to infrared reflectography (IRR), except that the light source is placed behind the canvas, painting, or drawing so that the light is transmitted through it. It has proved especially useful in discovering artists’ changes that are not visible in X-ray or infrared images, as well as original canvas stamps obscured from view as a result of lining.

• transmitted-light imaging

  • Imaging a work of art, usually with a canvas or paper support, illuminated from behind so that the light passes through the artwork.

• twill weave

  • Diagonal pattern of weaving.

• ultraviolet radiation

  • See UV (ultraviolet).

• underdrawing

  • Compositional sketch drawn usually directly on top of the ground layer in painting or directly onto the paper support in watercolor. Underdrawings can vary in media and level of detail, from simple contours to drawings that are volumetric and heavily detailed.

• underpainting

  • The initial painted layers of a work, which are often subsequently covered. Underpainting can include the initial laying in or blocking in of major compositional forms. Also called ébauche.

• UV (ultraviolet)

  • Invisible to the naked eye, UV radiation has energies beyond the visible light portion of the electromagnetic spectrum. Materials at the surface of an artwork may exhibit fluorescence in characteristic colors in response to UV radiation, depending on their chemical composition. For example, zinc oxide typically has a greenish-yellow fluorescence when viewed under UV, while certain red lakes often display a pinkish-orange fluorescence. UV-induced fluorescence is visible to the naked eye and can be documented photographically. UV imaging is used to help verify or differentiate surface coatings, pigment composition, and reworkings or restorations and can aid in their identification when coupled with other means of point analysis. UV radiation is also routinely used to study the fluorescence from constituent layers of cross sections under a microscope.

• UV fluorescence

  • See UV (ultraviolet).

• vanishing point

  • A point on the horizon where parallel lines executed in linear perspective meet. See also linear perspective.

• varnish

  • Resin-based surface coatings on a work of art. Spirit varnishes are made with resins dissolved in a volatile solvent that harden to form a film as the solvents evaporate. These coatings are usually transparent and are intended to protect the surface of a painting from grime and pollution, saturate the colors, and produce a consistent surface gloss.

• warp thread

  • Fixed longitudinal threads on the loom during the weaving process.

• warp-angle map

  • See thread-angle map.

• warp-thread match

  • Two or more canvases that match in overall thread count (average and distribution) and have thread-density patterns that appear to match in the warp direction. This indicates that the canvases originated from the same bolt (100–200-meter length) of raw canvas. The canvases are aligned laterally on the bolt, but their distance apart cannot be determined. Thread counts and density maps are generated by Thread Count Automation Project software.

• warp-thread repair

  • A starburst-like feature of a weft-angle map—generated by Thread Count Automation Project software—that corresponds to a repair made to the warp thread of a canvas during the weaving process. See also thread-angle map.

• wash

  • Thin paint layer produced by diluting the paint with water or solvent, depending on the binding media. Washes tend to appear more matte and are more liquid than glazes or semiglazes.

• watermark

  • Formed in paper by attaching wire designs (such as coats of arms, crests, or letters) to the paper mold screen; fewer fibers collect over the wire designs during the sheet formation, resulting in thinner areas visible in transmitted illumination. Watermarks can be studied to learn more about the paper’s date and manufacture.

• wax-resin lining

  • Process of lining a painting using a mixture of wax and natural resin as the adhesive. See also lining.

• weave

  • Woven pattern in textiles created by overlapping warp and weft threads. Common weave patterns include plain, or tabby, weave; twill; and basket weave.

• weave match

  • Two or more canvases which match in overall thread count (average and distribution) and have thread-density patterns that appear to match. Thread counts and density maps are generated by the Thread Count Automation Project software. Also called bolt match.

• weft thread

  • In the weaving process, the weft threads are laterally woven through the fixed warp threads.

• weft snake

  • A feature of the weft-angle map—generated by the Thread Count Automation Project software—that appears as a row of weak, cusping-like features away from the edges of the painting and corresponds to a hand-weaving fault. See also thread-angle map.

• weft-angle map

  • See thread-angle map.

• wet-in-wet

  • The application of wet paint onto a still-wet paint layer; the two paints may be blended or mixed together on the canvas. The presence of wet-in-wet paint application can be used to identify parts of a picture that were painted within a short time frame. Also called wet-into-wet.

• wet-on-wet

  • The application of wet paint onto a still-wet paint layer without mixing or blending the two paints.

• wet-over-dry

  • The application of wet paint onto a paint layer that has already dried or set up. This generally indicates some passage of time between the two applications. Also called wet-on-dry.

• wove paper

  • A type of handmade or machine-made paper formed on a mold screen of finely woven wires lacking the pattern of laid and chain lines. When the paper mold is dipped into water containing a fine dispersion of paper fibers, the fibers settle onto the wire screen as the water drains off; the formed sheet bears the wove wire screen pattern that is most clearly seen when light is transmitted through the paper sheet.

• X-radiography

  • X-radiography involves exposing a painting to X-ray radiation and imaging the transmitted X-rays on film or digitally. Materials vary in their ability to absorb or transmit the radiation, depending on their thickness, density, and chemical composition. X-radiography can reveal changes in composition, artist’s brushwork, damages, and details in the support not visible to the naked eye. Because all of the layers of the painting are superimposed on one plane, the reading of X-ray images (commonly called X-rays) requires careful interpretation.

• X-ray

  • See X-radiography.

• XRF (X-ray fluorescence spectroscopy)

  • This noninvasive means of analysis utilizes a focused beam of X-rays to excite the atoms that constitute the artwork and successively analyze the fluorescence emitted by the investigated species. It provides a characteristic fingerprint of the elements contained in the sample area, thus allowing the identification of the work’s inorganic components (pigments, extenders, metallic elements, and the like, but not binding media or organic pigments).

Click a glossary term on the left to view its definition.