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abrasion: A paint loss caused by excess friction during improper varnish removal or a varnish loss caused by friction.
acrylic: A family of synthetic resins made by polymerizing esters of acrylic acids.
alkyd: A synthetic resin which is the condensation product of a polybasic acid such as phthalic, a polyhydric alcohol such as glycerin and an oil fatty acid.
alla prima: An Italian phrase meaning painted solely wet in wet and usually, but not necessarily, at a single sitting. It is used most commonly with reference to oil painting.
binder: The nonvolatile portion of a coating vehicle which is the film-forming ingredient used to bind the pigment particles together.
blanching: A term applied to lacquer when they become partially opaque, cloudy or transparent upon application or drying. Fast-evaporating solvents may cool the film enough to cause water condensation, precipitating solid materials.
blending: Blending is most commonly used with reference to academic painting to mean the blending together of separate touches of color for half tones until the graduations of tone and the marks of the brush are imperceptible.
blocking-in: Usually refers to the broad application of masses of light, shade, and color, in the early stages of a painting. It helped to obliterated rapidly the glaring bright of the ground.
bloom: A bluish fluorescent coat which forms on the surface of some films.
body: Common term for the degree of viscosity of a paint or varnish, as "a lot of body" or "not much body." A practical term used to give a qualitative picture of consistency.
chalking: The presence of a loose powder on the surface of a paint after exposure to the elements.
chiaroscuro: The use of graduation of light and dark to describe forms in drawing and painting.
color: A generic term referring exclusively to all colors of the spectrum, including white and black. Color is described by three properties: hue, lightness and saturation. (1) Hue (color, character, dominant wavelength): blue, green, red, etc. (2) Lightness (brightness, reflectance, value): position on the gray scale between pure black and pure white (3) Saturation (purity, grayness, cleanliness, muddiness, chroma): purity or intensity of color.
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 film.
crawling: The tendency of a liquid to draw up and bead on the surface.
crazing: Fine lines or minute surface cracks occurring on painted surfaces due to unequal contraction in drying or cooling.
crocking: Removal of color on abrasion or rubbing.
drier: Any catalytic material which when added to a drying oil accelerates drying or hardening of the film.
drying oils: Oils which have the property of forming a solid, elastic surface when exposed to air in thin layers. The drying oils most commonly used in oil painting were linseed oil, walnut oil and poppy oil. Examples of non-drying oil unsuitable for painting are olive oil and almond oil.
efflorescence: A phenomena whereby a whitish crust of fine crystals forms on a painted surface. These are usually sodium salts which diffuse through the paint film from the substrate.
egg tempera painting: Egg (either whole, yolk or white) can be used as a pigment binder. Tempera painting was very popular until the late fifteenth century.
emulsion: A suspension of fine particles or globules of a liquid within a liquid.
enamel paints: Historically, enamel has described decorative and protective glassy coatings on metal as well as glassy, decorative coatings on glass. Enamel has also implied certain organic coating such as paints or lacquers.
extender: A pigment which contributes very little hiding to the system, but does reinforce the film and alter the gloss.
fly specks: The bodily waste discharged by flies. Fresh specks can be cleaned off with moistened cotton swabs; however, aged specks can not be cleaned off at all.
fugitive pigment: A phrase used to describe a pigment's impermanence and tendency to fade or change color under the influence of natural effects such as sunlight.
gesso: Traditionally a lean layer of size and chalk to form a ground on which to paint.
glair: Egg white. It is used in egg tempera painting and as a coating material.
glaze: 1) To cover paler under painting with a layer consisting of transparent pigments and excess medium. Traditionally used to add color to forms modeled in monochrome opaque paint. 2) To impart a glass-like surface. Aged glaze is very sensitive to solvents.
gloss: The shine, sheen or luster of the surface of a coating. Specular gloss: the ratio of reflected to incident light at specified angles of incidence. Most common are angles of 20, 60 and 85 degrees. See also sheen.
grime: Surface dirt: a combination of air-borne soot, nicotine, and cooking grease. Dirt can be in the varnish, on top of the paint layer, or on top of the varnish.
ground: A layer of opaque paint applied to a support to provide a suitable color and texture on which to draw or paint.
haze: The dullness of a surface removable by polishing. It usually results from faulty solvent balance or incompatibility of ingredients.
impasto: The texture created in a paint surface by the movement of the brush. Impasto usually implies thick, heavy brushwork, but the term also refers to the crisp, delicate textures found in smoother paint surfaces.
inpainting: Paint applied over losses only. This is a technique commonly used by conservators to unify a painting that has suffered paint loss.
lacquer: A term which usually indicates that the material dries by evaporation and forms a film from the nonvolatile constituents.
lake: A colored natural or synthetic dye absorbed onto a semi-transparent base and used as a pigment.
latex: a generic term describing stable dispersions of resin particles in a water system.
leaching: When solvents are applied to a paint film, solvent soluble compounds are removed and the film becomes more brittle.
lean paint: Lean oil color is paint in which the oil or fat content has been reduced, usually by indirect means such as diluting the paint with turpentine.
light fastness: (1) ability to withstand color changes on exposure to light (2) the relative degree of change or lack of change in color of materials exposed to the same amount and character of light.
lightness: (Brightness, reflectance, value) Position on the grey scale between pure black and pure white.
linseed oil: The most popular drying oil used as paint medium. The medium hardens over several weeks as components of the oil polymerize to form an insoluble matrix. Driers can be added to accelerate this process.
loaded: A painting is said to be loaded when it is painted thickly, often with a heavy impasto. A loaded brush is one charged to its full capacity with paint.
luster: The gloss of a finish.
medium: The component of paint in which the pigment is dispersed.
mildew: Organic surfaces exposed to high temperature-humidity atmospheres are attacked by fungus growth. This dark discoloration, usually a mold type of fungus but more commonly called "mildew."
mineral spirits: A petroleum fraction with boiling range between 300 to 400ºF.
mottling: A film defect associated with spraying. Appears as circular imperfections.
natural varnish: Tree resins (mastic and dammar), fossil resins (copal and amber), and insect resin secretions (shellac).
oil: A general term from a water-insoluble viscous liquid
oleoresinous: Indicating a material which has been made by the combination of an oil and a resin.
opacity: Hiding power or the degree of obliteration.
opaque: Impervious to light or not translucent.
orange peel: A pebbled film surface similar to the skin of an orange in appearance. It is caused by too rapid drying before leveling takes place.
over paint: This paint was not applied by the artist but applied at a later date. It not only covers the original paint, but its presence often indicates an excessive alteration of the image. Over painting is not an acceptable conservation technique.
paint layer: The paint layer is the actual layer or layers of color more-or-less opaque applied by the artist in the execution of the painting.
pentimento: Derived from the Italian meaning "repentance." Pentimenti are the changes in composition which a painter makes while producing a painting. These alterations are often visible in the infra-red, to x-rays and sometimes to the naked eye.
pigment: A finely divided, insoluble substance which imparts color to the material to which it is added.
polar solvents: Solvents such as alcohols, ketones, etc., which contain oxygen, etc. These have high dielectric constants.
polymer: A large molecule formed when many molecules are linked together by polymerization.
priming: The application of sizes and/or grounds to a support to prepare the painting's surface, modify its absorbency, texture and color.
resin: An organic polymer in the form of a crystalline or amorphous solid, or viscous liquid, of wither natural or synthetic origins.
retouching: The work done by a restorer to replace areas of loss or damage in a painting.
sagging: The tendency of a wet paint film to flow downward and become thicker on vertical surfaces.
saturation: Purity or intensity of color. Degree of freedom from grayness.
scumble: Very thin layer of opaque or semi-opaque paint that partially hides the underlayer.
shade: The difference in appearance between colors of similar hue.
sheen: A specular reflectance taken at a low angle, usually 85 degrees.
sinking: The absorption of paint medium by a lean underlayer to produce a matte or dead surface.
size: An adhesive diluted in water. Usually means and animal glue consisting of collagen and gelatin, rabbit skin glue, parchment glue, and edible jelly are all forms of gelatin.
stretcher: A rigid wooden frame over which a canvas is usually stretched. The stretcher can be expanded by tapping keys (wedges) inserted at the corners.
strainer: A stretcher from with fixed corners. It cannot be expanded.
synthetic resin: Complex, substantially amorphous organic semi-solid or solid materials built up by chemical reaction of simple molecules.
synthetic varnishes: Polyvinyl acrylate.
tacking edges: The outside edges of a stretched canvas through which tacks are inserted attaching it onto the stretcher.
tempra: Usually refers to egg (either whole, yolk, or white) used as the medium but can also refer to glue size.
thermoplastic: The term applied to resins which soften and flow when heated.
thermosetting: The term applied to resins which become hard after heating and cannot be resoftened.
toughness: The ability of a material to take bending, impact, etc., without cracking.
turpentine (spirits): The traditional solvent or thinner for a drying oil (such as linseed oil) distilled from the resin that is exuded by certain trees, e.g., the European larch, white fir, and American longleaf pine.
ultraviolet: The light rays which are outside of the visible spectrum at its violet end.
varnish: An applied surface film, usually of a transparent, cloudless resin. It imparts an even gloss to the surface, wetting the paint, and providing protection for it.
water sensitive binder: Glue, gum arabic, starch, cellulose esters. These materials were used by artists in the past and present in the construction of oil paintings.
white spirit: Turpentine substitute consisting of naphtha thinners (solvent distilled from petroleum). They are colorless hydrocarbons, boiling range 100 to 160ºC, used as a paint thinner.