Cleaning – process of removing dirt and/or discolored varnish from the painting surface. Cleaning is an irreversible treatment and one of the most demanding tasks of painting conservation.

Colorimetry – the science and technique of measuring colours according to objective criteria.

Fill/Filling – material (such as gesso or spackle) is used to replace lost paint and ground so that the area of loss becomes level with surrounding paint.

Fourier Transform Infrared Spectroscopy (FTIR) – an analytical technique that permits the classification of a broad range of organic compounds and some inorganic pigments. An FTIR microscope permits samples as small as about 10 microns to be used for this analysis.

Gesso – traditionally a lean layer of animal glue and chalk and/or lead applied to the support to form a white ground on which to paint.

Gloss – subjective term used to describe the relative amount and nature of mirror-like (specular) reflection. Trade practice recognizes the following increasing levels of gloss: Flat (or matte)—practically free from sheen even when viewed from oblique angles, Eggshell, Semigloss, and Full gloss—smooth and almost mirror-like surface when viewed from all angles.

Ground – the material applied to a support in order to prepare it for painting. The term is synonymous with the "priming." Different types of grounds can be loosely associated with different periods and schools of painting.

Impasto – the texture created in the paint surface by the movement of the brush. Impasto usually implies thick, heavy brushwork, but the term also refers to the crisp, delicate texture found in smoother paint surface.

Infrared Reflectography – an imaging technique for studying underdrawing and underpainting (the preparatory sketch on canvas that precedes the application of painting). Infrared light penetrates upper layers of paint and is then absorbed by the underdrawing. This differential absorption can then be imaged by an infrared-sensitive camera.

Lifting – separation of the paint layer from the substrate (ground or canvas in this case), often resulting in distortion or loss of paint.

Lining – a new piece of fabric attached to the reverse of a canvas painting, providing additional support for the picture.

Loss – describes a localized area of artist's material that is missing, perhaps causing a disruption in the design. Can apply equally to support, design layers, or coatings.

Photomicrograph – a highly magnified image taken with a camera attached to a microscope.

Polarized Light Microscopy (PLM) – an examination that permits the identification of pigments and fibers. Pigment particles used for PLM are typically in the size range of 1–20 microns, or less than a thousandth of an inch.

Raking light – the placement of a light source to one side of the painting at a low angle to the surface, so that the light glances across the painting. This examination reveals surface distortions, such as raised paint or undulations in the canvas.

Retouching/Inpainting – the work done by a restorer to replace areas of loss or damage in a painting. Contemporary conservation ethics dictate that retouching or inpainting must be confined to the specific area of loss and materials used must be reversible.

Scumble – to apply a thin layer of semi-opaque paint over a color to modify it. A scumble is a layer of paint used in this way.

Stretcher – a wooden framework that supports and maintains the tautness of a piece of canvas. Stretcher designs have been modified throughout the centuries.

Transmitted light – the placement of a light source behind the painting. With this technique, light is transmitted through cracks, tears, paint losses, and thinly painted areas, thereby differentiating them from more heavily painted areas.

Ultraviolet – ultraviolet (UV) illumination is used as a scientific aid in the examination of paintings. Because different painting materials exhibit characteristic fluorescence colors when exposed to ultraviolet light, UV illumination can be used to identify areas of retouching and to determine different types of varnish.

Underdrawing – a preparatory drawing directly on a ground, which is subsequently covered with paint. Such drawings are often executed with charcoal, chalk, pencil, or paint and brush.

Varnish – a coating applied to the surface of painting.

X-radiography – an imaging technique that is very helpful in revealing changes that may have occurred during the different stages of development of the painting. Pigments containing heavier metals absorb X-rays more than other pigments and X-radiographs register these differences, revealing changes of the composition by the artist as well as losses of original paint.

X-ray Fluorescence Spectroscopy (XRF) – a nondestructive examination tool that permits the characterization of most inorganic pigments through the identification of their elemental constituents.

Compiled by Piotr Rabicki, Education Intern, Department of Conservation with assistance from Chris McGlinchey, Conservation Scientist, The Museum of Modern Art

Sources

Bomford, D., J. Kirby, J. Leighton, and A. Roy. Art in the Making: Impressionism. The National Gallery Publications Limited, London, 1990.

Canadian Conservation Institute. CCI Notes. Ottawa, 1998.

Carr, D. W. and M. Leonard. Looking at Paintings: A Guide to Technical Terms. The J. Paul Getty Museum, Malibu, California, 1992.

Hansen, E. F., S. Walston, and M.H. Bishop, eds. Matte Paint, Its history and technology, analysis, properties, and conservation treatment. A Bibliographic Supplement to Art and Archeology Technical Abstracts, Vol. 30, 1993.