A glossary of common terms used in describing the materials and techniques of traditional oil painting

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

  • Abrasion — Changes to part of the surface coating, paint layer or paint and ground caused by scraping, rubbing or over-cleaning with an abrasive product.
  • Accretion — An accidental deposit of “foreign” material that was not part of the painting process. Dried liquid residue, foodstuff or fly specks are examples of these types of deposits.
  • Acrylic ground — acrylic dispersion grounds used in place of traditional gesso.  They are quite flexible, unlike gesso.
  • Alligator cracks or alligatoring — Drying cracks that resemble the pattern of certain animal skins, such as an alligator.


  • Binder or Binding Medium — the film-forming material that holds together the pigment particles in oil paint
  • Blanching — A localized, opaque, whitish discolouration in the paint or varnish layer. It can appear in spots on or in the surface of a painting or its coating. Blanching may occur when the binding medium in an oil film has been altered (e.g. by inappropriate cleaning) or when a varnish film has been degraded.
  • Bleeding — The spreading of paint into adjacent areas of a painting, which may be intentional (caused by the artist) or unintentional (caused by water or solvent action).
  • Bloom — A dull, cloudy film that appears on the surface of an oil painting that has been improperly varnished or stored.
  • BEVA 371 film — A heat-activated adhesive commonly used for attaching canvas to a support like a panel. It is easily reversible with heat or solvents.  BEVA 371 film is reversible with heat in the 130-140-degree Fahrenheit range.


  • Color Index Name Code — an international shorthand for identifying pigments that has been adopted by paint manufacturers. The first character, “P”, stands for pigment. The second represents the hue (for example, B for Blue, O for Orange). The final element is a number code for the colouring agent. 
  • Corner or Diagonal Cracks — Mechanical cracks often found at the corners of paintings. They can result from inappropriate keying out or from dropping the painting on its corner.
  • Cracks or Craquelure — Surface or deep checks in one or more of the varnish, paint or ground layers. Cracks are caused by a combination of mechanical forces and the response of the paint, ground and support layers to relative humidity fluctuations, periods of low relative humidity and low temperatures.
  • Cross Bar or Cross Brace — An extra horizontal or vertical piece added between the main bars to strengthen a strainer or a stretcher.
  • Cupping — On the surface of a painting: lifting in which islands of paint, separated by cracks, develop concave centres with raised edges, like shallow cups.


  • Drying Cracks — Cracks occurring during drying that can be wide, exposing paint layers or ground layers below, and that have rounded or sloping edges and no cleavage. Although frequently disfiguring, drying cracks are usually stable and do not spread.
  • Drying Rates


  • Feather Cracks — Mechanical cracks in a pattern resembling a feather which are caused by a line of contact against the back of the painting (e.g. a scrape) or a glancing contact on the canvas with a hammer when keying out.
  • Flaking — The partial or complete detachment of fragments of paint layers or ground from an underlying layer. Untreated flaking will result in the loss of paint layers and ground in the form of a lacuna.


  • Gesso — the traditional ground made from hide glue (aka rabbit skin glue), slaked plaster of paris, or white chalk as the pigment.
  • Glaze — A transparent layer (oil or resin-rich; usually pigmented) applied by an artist on the surface of a painting. The glaze can be composed of a single or multiple layers.
  • Glazing – The technique of applying a very thin, transparent colored paint over a dried painted surface to alter the appearance and color of the surface.
  • Ground — An opaque white or coloured preparation layer applied to the support as a base for the paint layers. Grounds were traditionally composed of chalk or white lead combined with glue or oil. Today, grounds formulated with modern pigments and acrylic medium are common.
  • Hardboard (or high-density fibreboard) — A compressed wood board that has a density of 800–1200 kg/m3 and that can be smooth on one or both sides. Hardboard is commonly found under the name Masonite.
  • Impasto — Paint standing in relief on the surface of a painting following pronounced brush strokes or the thick application of a layer of paint.
  • Imprimatura — A thin layer of paint applied over a ground by the artist to provide the base tone for the painting. The toning is usually done with a  transparent colour after the artist has transferred a drawing onto the ground and (in the Flemish technique) strengthened it with ink.
  • Lightfastness
  • Lightfastness Rating
  • Liquin — Liquin is an alkyd medium that speeds the drying of oil paints, and adds transparency. If one is to use it at all, the safest way is to add it to all layers in the painting, but Virgil suggests that the amount added be minimal.
  • Long paint — The terms ‘long & short’ refer to the consistency of paint squeezed from the tube. If you squeeze paint out of a tube and it comes out as a long, stretchy rope, it’s long. Long paint is, also, called “ropey.”


  • Mediums — oil painting mediums are used to modify the paint that comes out of the tube in some way. For example, if the paint has a stiff, pasty consistency, an artist might add some medium to it to improve its brushing characteristics.


  • Organics pigments — pigments that contain carbon.  Compared to inorganic ones (without carbon), they tend to be less opaque and stronger in tints. They will also hold their purity and brilliance better when mixed with other organics. Sometimes they get murky when mixed with inorganics. Synthetic organic pigments also tend to be more transparent, lighter in weight, and higher in tinting strength (Source: James Gurney, “Color and Light”. )
  • Opacity Rating — rating a pigment by its covering power.
  • Paints
  • Pigment Name
  • Pigments
  • PVA Size — Poly Vinyl Acetate Size — a neutral pH contemporary size for fabric support, best diluted with distilled water.  Recommended by conservation scientists over traditional rabbit skin glue.  PVA provides a good size layer that seals the fabric but does not re-absorb atmospheric moisture, swell and shrink like rabbit skin glue does. There are hundreds of different formulae of PVA.
  • Primer — a synonym for ground, and not to be confused with sizes, imprimaturas, or isolating varnishes
  • Priming — the act of applying a ground to a support.
  • Rabbit skin glue — a traditional size for fabric support and panel supports.  The size consisted of a hide glue that was melted in a double boiler with a white pigment (powdered chalk, slaked plaster of paris, or gypsum) and applied while still warm.  Rabbit skin glue tends to re-absorb atmospheric moisture, swell and shrink. It is a cause of cracking in old oil paintings on canvas. For that reason, conservation scientists recommend using neutral PH PVA size instead.
  • Scumbling — The technique of applying a layer of opaque paint over a previously painted passage of a different colour or tone. The lower layer is not completely obliterated, resulting in an uneven, broken effect.
  • Short Paint — The terms ‘long & short’ refer to the consistency of paint squeezed from the tube. If you squeeze paint out of a tube and it comes out like thick toothpaste, it’s short.
  • Sizing — a thin application of a substance that will mitigate the absorbency of canvas or wood to prevent oil from soaking into the cellulose fibers and initiating the rotting of them.  See PVA and Rabbit Skin Glue.
  • Tinting Strength — How much of a given paint is needed to tint a mixture the desired amount.  The less paint needed, the stronger the tinting power.
  • Toxicity
  • Transparency – One of the qualities of paints that can be exploited. To paint passages with the highest degree of transparency, choose transparent pigments, those consisting of relatively fine crystals.  Transparent paints are used for the deepest shadows, darks in the foreground and special effects.
  • Trompe L’oeil — A fool-the-eye realism wherein a shallow depth of field is employed in the setup. A typical setup is often a board or wall with small or relatively flat objects attached to it and strongly lit by a single light source. Each object depicted is rendered with the highest possible level of realism. Visible brushstrokes and painterly effects are eschewed in the interest of creating the most convincing illusion possible.
  • Turpenoid — a.k.a. odorless mineral spirits (OMS,) a mild solvent that is sometimes used in oil painting mediums in combination with linseed oil or stand oil, and for rinsing paint brushes. Note that the absence of detectable odor is not to be interpreted to mean that therefore it’s without potential health consequences of inhaling its vapors or ingesting it.
  • Turpenoid Natural —  a mixture of a citrus peel solvent and linseed oil. Turpenoid Natural has such powerful solvent action that it will eat through oil paint on paintings hundreds of years old, which makes it a good choice for cleaning brushes that have dried paint on them, but not a good choice for thinning oil paints or using as a painting medium or medium ingredient.
  • Underpainting
  • Varnish — Resins in oil or solvent, used primarily for protecting the surface of the painting.
  • Varnish Aging — Natural resin varnishes turn first golden in hue and then progressively darker with age, causing serious distortion of the artist’s original colours.

Search Traditional Oil Painting

Try searching for a specific term on our website. Some examples: safflower oil, burnt sienna, varnishing.