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Glossary of Technical Terms

Selected technical terms that appear throughout NGA Online Editions.

abrasion A gradual loss of material on the surface. It can be caused by rubbing, wearing, or scraping against itself or another material. It may be a deteriorative process that occurs over time as a result of weathering or handling or it may be due to a deliberate attempt to smooth the material. 
beveling Angling along the edge of a panel or a stretcher bar.  
blistering The bubbling or bulging of the paint surface. Blisters are caused by excessive heat, insufficient adhesion to the layers beneath, or trapped pockets of air, liquid, or solids.  
cradling Attaching a woodent grid to the reverse of a panel to prevent the panel's warping.  
craquelure The network of cracks in the paint and ground. Also sometimes referred to crackle pattern.  
cusping Distortions near the edges of the canvas caused by tension from the nails or tacks that hold it to the stretcher or strainer. Also sometimes referred to as scalloping.  
cupping Distortion of the paint surface resulting in raised areas along the cracks.  
dendrochronology  A method of dating wood by examining the annual growth rings.  
flaking Loss of pieces paint and/or ground.  
glazing Applying transparent layers of paint that influence the colors or tonalities of the layers below.  
ground  The layer or layers used to prepare the support to hold the paint.  
imprimatura A colored priming layer used to establish the tonality of the painting.  
Infrared Reflectography A photographic or digital image analysis method which captures the absorption/emission characteristics of reflected infrared radiation.  The absorption of infrared wavelengths varies for different pigments, so the resultant image can help distinguish the pigments that have been used in the painting or underdrawing.  
inpainting Application of restoration paint to areas of lost original paint to visually integrate an area of loss with the color and pattern of the original, without covering any original paint.
 
lining A second piece of fabric attached to the back of a painting's original support fabric for physical reinforcement.  
overpaint A layer of paint that covers original paint.  
palette knife A long, thin, flexible spatula used for mixing paint, for transferring paint to the palette, and occasionally used to apply paint to the canvas.  
pen painting A method of painting in which one draws in black ink on top of a substrate prepared with an oil ground.  
pentimenti An alteration made by the artist to an area that was already painted.  
planing The smoothing or finishing of a wood surface.  
retouching Application of restoration paint to areas of loss in order to visually integrate them with the color and pattern of the orginal. Retouching can refer to inpainting or overpainting.   
repainting Paint applied after a work is finished.  
scumbling Applying opaque or semi-opaque, dry paint so that it partially covers and modifies the color below.  
scraping An decorative technique that requires the artist's deliberate removal of paint.  
sketching Drawing quickly to record a composition or the most significant features  of a subject.  
splintering The splitting or breaking of a wooden panel into sharp, slender pieces.  
support, canvas The fabric on which a painting is executed.  
support, transfer The removal and reattachment of the paint and sometimes the ground layer to a new support.  
support, panel The wooden panel on which a painting is executed.  
tacking margins The border of a canvas that is wrapped around the stretcher or strainer and tacked or stapled to the wood.  
tearing The deterioration or ripping of canvas.  
underdrawing A drawing executed on a ground before paint is applied.  
underpainting An initial layer of paint applied to a ground that begins to define shapes and values.  
warping Distortion in wood caused by instability.  
workshop The apprentices and employees who work within an artist's studio.  
wrinkling Small furrows and ridges in paint or fabric due to shrinkage, folding, or compression.  
X-radiography A photographic or digital image analysis method that visually records an object's ability to absorb or transmit  X-rays. The differential absorption pattern is useful for examining an object's internal structure as well as for comparing the variation in pigment types.  
Ultraviolet light (examination) Using the part of the light spectrum to study the fluorescence of varnishes and repaint.