Asphaltum
Also called bitumen, a naturally occurring tarry compound. Mixed with oil it produces a rich, semitransparent, warm brownish black that has been used by painters since ancient times. Asphaltum never fully dries and can cause disfiguring cracks, particularly if used thickly. When properly prepared and handled, as by Rembrandt or Rubens, its inherent problems can be minimized. [ top ]
Beveling
On a panel support, the paring down of the back edges to an angle to facilitate fitting the finished painting into its frame. Since this was a common practice in Rembrandt's time, the absence of a bevel on one or more sides can indicate that the work has been cut down. [ top ]
Cartoon
A full-size preparatory drawing for transfer to a painting. The word derives from the Italian cartone, the heavy paper on which such designs were made. [ top ]
Chiaroscuro
From the Italian chiaro (light) and oscuro (dark), the depiction of light and shadow in paintings. The term is generally associated with dramatic effects, as exemplified in the work of artists such as Caravaggio, Georges de La Tour, and Rembrandt. [ top ]
Cross section
A sample used in the examination of materials and layer structure of a given point on a painting. These minute paint samples (typically 1/2 mm across) are embedded in resin. Once solidified the composite is ground down to expose the paint stratigraphy and examined with reflected light under a microscope. Magnification is generally 100-300x. Cross sections can also be examined under ultraviolet reflected light (see Fluorescence). In addition to providing a view of the buildup of the paint, cross sections sometimes allow for the identification of pigments optically or by using various instruments for elemental analysis. [ top ]
Dead coloring
The preliminary blocking in or underpainting that establishes the tonal values of a picture and serves as the base for overlying paint layers. The process is described in Karel van Mander's highly influential Het Schilder-Boeck of 1604. (See Lay in and Underpainting) [ top ]
Dendrochronology
A method of dating wooden objects, including panel supports used for paintings, based on examination of the annual growth rings of trees. The width of these rings varies according to climate and other conditions that determine growth. When compared with established chronologies of tree rings, the sequence of the rings in a given board indicates the felling date of the tree from which it was taken and thus provides at least the earliest possible date of its use. This terminus post quem assists in placing a painting in an artist's oeuvre. [ top ]
Fluorescence
Certain materials-media, varnishes, and a few pigments such as organic lakes-emit visible light, or fluoresce characteristic colors and intensities, when excited by ultraviolet (UV) light (q.v.).When the surfaces of paintings are examined under illumination from UV lamps in darkened rooms, additions or retouchings can sometimes be observed since these often appear dark in relation to paint layers and varnish, both of which can fluoresce more strongly with age. [ top ]
Glaze, glazing
A layer or layers of translucent paint applied over an opaque and generally lighter underlayer, which acts like a colored filter to modify and enrich color and/or create a sense of depth. The glazing technique is best exploited in oil painting, where the transparency of the paint permits the production of a wide range of tone and hue. The terms apply to both the paint film and the technique. (See Lake pigments) [ top ]
Ground
The overall preparatory layer or layers of material applied to a support as a structural and coloristic base for subsequent painting. Rembrandt and painters of his circle frequently used so-called double grounds applied in two layers, often of different colors. [ top ]
Haptical
Relating to or based on the sense of touch. In Rembrandt's paintings the term can be used to describe the creation of textures of extraordinary tactility through the use of variegated brushwork and scratching into paint. (See Impasto) [ top ]
Impasto
Paint applied in thick or heavy strokes that stand out in relief [ top ]
Imprimatura
Also called priming, a thin paint layer applied over the ground either generally or locally to modify its color or tone in preparation for subsequent painting [ top ]
Infrared reflectography
An analytical imaging method that uses infrared (IR) radiation for the study of underlayers and underdrawings invisible to the naked eye (infra is Latin for below). Infrared wavelengths are just longer than those of the visible light spectrum. IR radiation penetrates certain colors and reveals images that arise from the contrast between materials that absorb IR--such as carbon-based pigments used in painting and underdrawing materials- and materials that reflect IR--such as white pigments often used in grounds. While IR photography using sensitized film records images derived from the near infrared, IR reflectography uses a video system incorporating an IR tube and is sensitive to a longer wavelength of radiation that can better penetrate the upper paint layers. IR imaging techniques are particularly well suited to the study of fifteenth- and sixteenth-century Northern European panel paintings. Their application for works of Rembrandt and his school is generally limited to panel paintings, for which they have been used to clarify darkened shadow areas. [ top ]
Lake pigments
Pigments made by precipitating a dyestuff onto an inert base such as aluminum hydroxide. Until organic dyestuffs were synthesized in the nineteenth century, the coloring material of lake pigments was derived from various natural sources, both vegetable and insect; rose madder, for example, is made from the herbaceous perennial Rubia tinctorum. Lake pigments are translucent, particularly in oil, and are often used for glazing. (See Glaze, glazing) [ top ]
Lay in
A preliminary rough blocking in or underpainting (q.v.) [ top ]
Macrophotography
The technique used to photograph details of paintings, either one-to-one or enlarged, using a camera with a short-distance focusing lens. Macrophotographs provide a very precise record of a picture's surface, showing brushwork, crack systems, and other minutiae and are invaluable tools for the study and documentation of technique and condition. [ top ]
Microphotography
The technique used to photograph details of a painting using a microscope and thus always larger than one-to-one. Microphotographs record features too fine for the naked eye to discern, such as the size and distribution of pigment particles, minute damages, and retouches over cracks. [ top ]
Modello
Italian for model, used to describe a small preliminary version of a painting. A modello can be either very sketchy or highly finished; it often served as a demonstration piece for a patron or as a working model for assistants. [ top ]
Morellian
The term applied to the quasi scientific approach to connoisseurship invented by the Italian art critic Giovanni Morelli (1816--1891). Morelli's method of attribution concentrates on the characteristic manner in which different artists depict certain secondary features (such as hands or earlobes). [ top ]
Neutron activation autoradiography
A method of generating images from the chemical elements that make up the various pigments and other materials used in paintings. The painting is irradiated with lower energy thermal neutrons in a nuclear reactor, creating faint, transient radioactivity of its materials. The emitted radiation of the different elements is recorded on a series of photographic films placed in close contact with the painting for predetermined periods of time over a number of weeks. Blackened areas that appear on the film when it is processed show elements emitting radiation at specific times, determined by their half-life. For example, four days after irradiation, calcium and phosphorus, elements of bone black pigment, are the principal generators of the autoradiographic images shown in this catalogue. Since the distribution of pigments results from the painting process, neutron activation autoradiography provides a unique insight into an artist's working methods and also provides information about condition. However, the superimposition of imaged emissions from different layers can make the radiographs difficult to interpret. [ top ]
Panchromatic film
Panchromatic emulsions, used in film for both black and white and color photography, are sensitive to all visible wavelengths (pan is Greek for all). Silver halides, which were used in the earliest photographic emulsions, are mainly sensitive to the blue-violet end of the spectrum. Dyes were added to extend the range of sensitivity to all visible wavelengths – to green light in the 1880s and to red in 1905; further refinements followed. The introduction of panchromatic film brought about a great improvement in the quality of illustrations. [ top ]
Primary colors
In painting these are the three colors red, yellow, and blue, from which all others can be made, according to a theory first recorded in print in the seventeenth century. The secondary colors orange, green, and purple are made by mixing two of the three primaries. An individual pigment reflects a portion of the spectrum and absorbs the rest. Therefore mixtures of paint conform to a subtractive system whereby the perceived brightness of the reflected light is progressively diminished with each addition; a mixture of all three primaries creates a muddy brown. In colored light, on the other hand, the primaries are red, green, and blue. Mixtures of colored light conform to an additive system; superimposition of red, green, and blue light produces white light. The difference between additive and subtractive primaries was not fully understood until the early nineteenth century. [ top ]
Priming (See lmprimatura) [ top ]
Principaels
The archaic Dutch term for portraits done from life that served as the models for copies made for members of the sitter's family. Seventeenth-century Dutch inventories indicate that the production of such portraits, which were generally of high quality, was a conm10n practice in the Netherlands. [ top ]
Pentitnento
An artist's alteration-literally "change of mind"- to an already painted area. Pentimenti sometimes become more apparent with age, and they also can be revealed through X radiography (q.v.), neutron activation autoradiography (q.v.), or infrared reflectography (q.v.). [ top ]
Quartz
A naturally occurring form of crystalline silica, SiO2 . Silica is one of the most commonly found minerals on the earth's surface and is a relatively inexpensive material. It was used as a filler component in grounds (q.v.) by Rembrandt and members of his circle. [ top ]
Retouching
Traditionally, artists' final touches or revisions. The term is also used to describe a procedure in the restoration of pictures in which areas of old loss or damage are inpainted to a greater or lesser degree to make them less obtrusive and less distracting to the viewer. In modern conservation, guidelines dictate that such retouching or inpainting should be reversible and limited to the area of loss. Although the need to observe these strictures may seem obvious, in the past restorers have taken considerable liberties in the form of retouching over original paint. Within modern guidelines different philosophies operate, and latitude regarding the extent of retouching is left to the individual conservator, who determines what is appropriate in a given situation. Most conservators aim to render loss or damage invisible with retouching, but there are other approaches, including the use of a neutral tone or applying retouching that is visible at close quarters but indiscernible from normal viewing distance. [ top ]
Scalloping
Also called cusping, garlanding, and stretchmarks, these are the local wavy distortions at the canvas edge caused by the initial stretching of the canvas. In Rembrandt's time this stretching was generally done by lacing the canvas within a loom or framework. Scalloping is sometimes easier to discern in an X radiograph than on the actual picture surface. The absence of scalloping on one or more edges can indicate that the support is a section of a larger prepared canvas or that the finished work was cut down. [ top ]
Scrumble
A thin semi opaque paint layer applied over a darker underlayer; the two layers combine optically to create a cool, hazy or subdued effect. The term can also be used as a verb, indicating the technique. [ top ]
Sketch
A freely executed study, drawn or painted, either functionally related to a finished work or an end in itself. The term is also used for the rough underpainting stage of a more finished painting. [ top ]
Strainer
A wooden framework with fixed corners for stretching canvas [ top ]
Stretcher
A wooden framework with expandable corners for stretching canvas. Wedge-shaped keys are inserted into slots in the inner corners to expand the stretcher in order to make a slackened canvas taut again. Keyable stretchers were introduced in the mid-eighteenth century. Until then canvas was usually stretched on strainers (q.v.). [ top ]
Tacking edge
The margins of a canvas that are folded around and tacked to the edges of a stretcher or strainer [ top ]
Tomography
A technique of X radiography that shows details in one plane in focus and blurs those in adjoining planes [ top ]
Transfer
A procedure in which a picture's original support is separated from the paint and ground and replaced with a new support. In the process the original ground may also be removed. This radical intervention is seldom undertaken in modern conservation practice. [ top ]
Tronie
Archaic Dutch term meaning head or face or facial expression. Tronies are not portraits but representations of imaginary subjects. [ top ]
Turbid medium effect
An optical effect whereby, according to Rayleigh's law, light objects seen though a turbid medium, that is, a semi opaque layer or veil, appear warm (for example, the light of the setting sun seen through the earth's atmosphere) and, conversely, dark objects seen through a turbid medium appear cool (for example, distant mountains seen through mist). By extension, the same translucent paint film appears warm over a light underlayer and cool over a dark underlayer. Painters have long exploited the effect. (See Scumble) [ top ]
Ultraviolet
The more energetic portion of the electromagnetic spectrum just beyond the visible region. (See Fluorescence) [ top ]
Underpainting
A paint layer or layers applied in anticipation of subsequent layers. It can take many forms, indicating the composition as well as the tonal and color values or serving as the base for glazes and scumbles. [ top ]
X radiography
An analytical method used in the examination of the structure, technique and condition of paintings. X-ray sensitive film is placed in contact with a painting. Low-voltage X rays pass through the painting and then through the film. The processed film, which is called an X radiograph, shows an image that reveals the degree to which the X rays have penetrated or have been blocked by the materials present, depending on their density and distribution. Viewed on a light box, the denser elements appear light and those less dense appear dark. It is generally possible to read both the paint and ground layers in traditional paintings because of the ubiquitous use in them of lead white as well as other pigments derived from heavy metals and to a lesser degree of pigments made from iron earths. Because light areas on the painting containing lead white also appear light on the X radiograph, a close correlation between the two images is often observed, but since all layers are superimposed X radiographs require careful interpretation and direct comparison with the subject. [ top ]
X-ray diffraction analysis (XRD)
A technique for identifying materials of crystalline structure, which include many pigments. A beam of X-rays targets a microscopic sample in a type of camera housing. The crystalline structure of the sample deflects the X rays and creates a diffraction pattern on photographic film, which is compared to known standards. Since crystalline pigments have a clearly identifiable structure the results obtained from XRD are unambiguous. [ top ]