K Relations Between Measured and Calendar Age
The basic assumptions of radiocarbon dating are a constant rate of radioactive decay uninfluenced by external factors and constant concentration of 14C in the biosphere. The first assumption has been found correct. The second assumption has been found only approximately correct. The rate of 14C production depends on the stability of cosmic-ray flux. Dendrochronology tree ring dating method together with high precision 14C dating allowed for measurement of variation in 14C production back to...
b Reflection and Scattering
When light is incident on a transparent material such as glass, the light is reflected from the surface as well as refracted as it passes into the material. As shown in Figure B.4, the angle of incidence i is equal to the angle of reflection i' angle of incidence i angle of reflection i' B.4 Fig. B.4. The paths of rays of light incident on a glass plate at angle of incidence i and then about 4 reflected at the air glass interface and the remainder refracted at an angle r. As the light ray exits...
b Hiding Power
Hiding power is the measure of a paint's ability to cover a surface opaquely so that an underlying paint cannot be seen in visible light. Absorption is one factor in the hiding power of a paint. Darker colors absorb more intensely than lighter colors and hence have a greater hiding power. The refractive index can play a major role in determining hiding power. The amount of light scattered or reflected from the interface of a composite of two materials depends strongly upon the difference...
Color Characteristics
Homage to the Square Saturated, a painting by Josef Albers Color Plate 10 , is composed of overlapping red squares. The squares differ from each other, and these differences can be accurately described by noting three characteristics hue, value, and saturation. Hue identifies the color red, in this case as distinct from other hues yellow, green, or violet, for example . Value is the lightness or darkness of the hue as it relates to a scale of white to black Figure 4.2 . We can distinguish one...
Pigment Response to Xrays Emission
Pigments have been characterized by their color and their relative transparency to infrared and x-radiation. The induced emission of x-rays also provides a means for pigment identification. An incident x-ray photon is absorbed and an electron is ejected from the atom, leaving an unfilled state. There is a specific set of energy states occupied by the electrons. No two electrons can occupy the same state. An electron in the atom makes a transition to fill the empty state, and an x-ray is...
I Polarized Light Microscopy
The polarizing light microscope is used in the study of materials of paintings because one can identify crystalline pigment materials. The unique characteristic of the polarizing microscope Figure I.7 is the presence Biaxial Crystals, the Pigment, and Refractive Indices Data from Brill, Light Plenum Press, New York, 1980 Data from Brill, Light Plenum Press, New York, 1980 Fig. I.7 Incident light is polarized and passes through the sample and crossed polar analyzer to an image of a brightly...
C Infrared Reflectography and Hiding Thickness
When it comes to the study of under-sketching rather than underpainting, scientific emphasis switches to infrared reflectography. X-rays are scarcely able to make any distinction between a plain chalk ground Fig. C.6 and one only slightly altered by addition of a thin sketch line in charcoal and bone black. But infrared radiation of wavelengths around 2.0 microns, having penetrated the upper paint layers, in particular the pigment, will be reflected at the level of the sketch and by virtue of...
Pigment Response to Neutrons
A beam of neutrons incident on a painting will induce reactions within the elements present in the pigments. These reactions lead to the emission of beta rays and gamma rays. As is the case in x-ray emission, the energies of the emitted gamma rays identify the elements. Beta-ray emission allows one to examine the distribution of elements across a painting in a manner similar to x-radiography. An autoradiograph of Anthony Van Dyck's Saint Rosalie Interceding for the Plague-Stricken of Palermo...
K Accelerator Mass Spectrometer
A new era of application of radiocarbon dating came with development of the alternative method of 14C detection based on direct analytical determination of the concentration ratio of 14C and stable carbon isotopes in the analyzed sample K7 . The conventional 14C counting methods provide information about concentration of 14C in the sample based on radioactive decay and measurement of beta particles emitted from the sample. A more efficient method for 14C measurement would be a direct analytical...
Encaustic
Wax has been used as a binding agent in paint since antiquity, and the most compelling examples of its use to date remain the famous portraits produced at Roman settlements in Egypt during the first and second centuries a.d. Figure 2.11 Portrait of a Woman, J. Paul Getty Museum . The simplest method of wax painting is called encaustic, a term derived from Latin and referring to the use of heat, which is required to liquefy the colors. In modern usage, a bleached white beeswax is combined with...
Dating and Pigment Identification
At this point we go beyond routine visual examination procedures and attempt to date the painting. The suspect work of art can be dated by dendochronology Appendix L if a wooden panel support is used or by carbon-14 techniques Appendix K if a canvas is used as support. One can also reach conclusions about a painting's date by determining the elemental composition of inorganic pigments. Element identification can be made by x-ray fluorescence, XRF Appendix F , or by particle-induced x-ray...
Fluorescence
Photons of visible light are not absorbed in layers of varnish and binding media but are transmitted through them. In contrast, the higher-energy photons in the ultraviolet UV region of the spectrum are strongly absorbed in varnishes and binding media. The absorption of ultraviolet photons results, in some cases, in the emission of photons in the visible region of the spectrum. The absorption of light photons of high energy and reemission of photons of lower energy, in the visible region, is...
Fresco
Fresco is an ancient technique of painting on masonry walls. The color in Diego Rivera's murals at the Detroit Institute of Arts Color Plate 6 was applied to damp plaster hence the term fresco, or fresh in Italian . The material used to paint frescos does not conform to our usual definition of a paint, which specifies the presence of a binder. The pigment is ground in water, which has no binding strength. Water is a vehicle, or diluent, which evaporates during the drying process. The water is...
Pigment
A leading manufacturer of artist's paint currently lists at least 108 different colors of oil paint. The pigments selected for these colors are uniform in particle size, compatible with oil binders, are reasonably resistant to atmospheric gases and light, and are for the most part permanent. These modern pigments are also relatively uniform in consistency, workability, and drying time from color to color. Even though some of the 108 colors are mixes of two or more pigments a flesh color might...
The Chromaticity Diagram
The sensation of color depends primarily on the composition of light, which is a mixture of white light and colored light which in itself can be a mixture of wavelengths as in the case of purple . The colored light may have a dominant wavelength, or hue, and the extent to which the hue dominates is known as saturation or chroma . The saturation decreases as the hue is diluted with white light. There are three types of receptors in the eye that respond to different wavelengths Chapter 4 . This...
b Artists Pigments Materials and Methods
B-1 R.L. Feller, Ed. , Artists' Pigments National Gallery Art, Washington, 1986 6th edition. B-2 A.P. Laurie, The Painter's Methods and Materials Dover Publications, New York, 1967 . B-3 A. Roy, The Materials of Van Gogh's Cornfield with Cypresses, National Gallery, Technical Bulletin, Vol. 11, pp 50-58, 1987. B-4 D.V. Thompson, The Materials and Techniques of Medieval Paintings Dover Publications, New York, 1959 . B-5 R.H. Harley, Artists' Pigments, c. 1600-1835 Butterworth Scientific, London,...
Tempera
Tempera refers to paint containing a binder of egg. Its vehicle is water, which dilutes the paint but evaporates during drying. Tempera produces a very durable but somewhat brittle paint film. It is usually applied to a rigid wooden panel Color Plate 7 that has been coated with gesso, a mixture of animal glue, water, chalk, and, at times, white pigment. The rigid support typically made of wood prevents the paint film from flexing enough to cause cracking or flaking. In order to maintain binding...
A Successful Forger
It is difficult to be a successful forger. Not only must the forger possess impressive artistic skills, he must have a general knowledge of a particular historical period as well as an understanding of the materials and methods employed by artists of the period. One starts with the support for European paintings the choices are wooden panels or canvas, depending on artist, time period, and geographic location. Both types of support can be easily dated, so the supports must be obtained from a...
h Fourier Transform Infrared Spectrometry
The infrared region of the electromagnetic spectrum is the region on the longer-wavelength side of the visible spectrum. Infrared radiation can not be seen by our eyes, but we sense it as heat all hot objects give off considerable infrared radiation . Infrared reflectography described earlier in this book, uses near infrared radiation, that is, infrared radiation just beyond the red part of the visible light spectrum. The infrared radiation used in IR reflectography goes out to wavelengths of...
Pigment Response in the Infrared
In the infrared portion of the spectrum the wavelengths are greater than 700 nanometers with photon energies less than 1.8 electron volts 76 eV . These infrared photon energies, typically around 1 eV, are so low that the photons are not absorbed by most pigments. The paint layers are therefore relatively transparent to infrared radiation. Infrared radiation penetrates the upper paint layers but is absorbed by dark preliminary drawings that reside beneath them. The remaining radiation is...
I Crystal Optics
The index of refraction n of a transparent medium is defined as the ratio of the velocity c of light in vacuum to the velocity v in the medium Glasses, liquids, and cubic crystals have a single refractive index and are optically isotropic the optical properties are independent of direction and orientation of the light to the crystal axes . Other transparent media with lower symmetry and more complex crystal structure than cubic crystals are optically anisotropic, and thus have more than one...
b Dispersion
The index of refraction or decrease in velocity depends on wavelength, with the velocity decrease more pronounced for blue light than for red. Thus, when parallel beams of red and blue light enter glass, the blue light is bent more at the air glass interface than the red light Figure B.6 . This spreading of the beam is called dispersion. The dispersion curve in the visible region of crown glass is shown in Figure B.7. Although the difference in refractive index between that for blue, n 1.51,...
Beyond Analysis
The analysis of paintings provides extremely valuable information to those concerned with the conservation, authenticity, and art-historical aspects of these very complex art objects. Analysis also establishes for the practicing artist a body of practical knowledge concerning historical methods and materials. We have made the general argument that the information obtained through scientific methods of analysis in conjunction with an understanding of how paintings interact with the forces of...
eNeutron Activation and Autoradiography
E-1 M. Ainsworth et al., Art and Autoradiography The Metropolitan Museum of Art, New York, 1982 . E-2 W.J. Young, Ed. , A.A. Gordus, Neutron Activation Analysis of Streaks from Coins and Metallic Works of Art in Application of Science in Examination of Works of Art Museum of Fine Arts, Boston, 1973 . E-3 B. Keisch, Secrets of the Past Nuclear Energy Applications in Art and Archaeology US AEC, 1972. E-4 E.V. Sayre et al., Eds. P. Meyers, The Structure of Works of Art and Historic Artifacts, in...
CrossSection Analysis of Sample from Detroit Industry by Diego Rivera
Contributed by LEON P. STODULSKI, Detroit Institute of Arts JERRY JOURDAN, BASF, Inc. Buon fresco technique requires applying very finely ground natural and synthetic alkali stable pigments suspended in water onto wet plaster. As the plaster sets by chemical reaction with atmospheric carbon dioxide, the pigments become an integral part of the wall surface. This produces a very tough, colored surface. The extent to which this technique produces pigment embedded in the wall's surface and not...
h Chromatography
Chromatography is the name for a group of analytical procedures widely used in the identification of many organic materials. The name for the general procedure came from its first application in 1906, when an extract from leaves was flushed through a column packed with calcium carbonate. The extract separated into a number of differently colored bands as it passed through the column. Each band essentially represented a different compound contained in the extract. All chromatographic techniques...
Examination and Analysis
We have described a painting as an object made from a variety of materials carefully chosen by the painter. But how is it constructed, what are its materials, and how is our visual response generated by the result of their combination A series of analytical techniques has been developed to help answer these questions. The techniques employed in the scientific analysis of paintings follow a sequence beginning with an external view with the unaided eye. Much information is available from this...
gi Nuclear Reactions
In this section we present the basic terminology and concepts involved in nuclear reactions. We are primarily concerned with two reactions 1 The nucleus can be excited to a higher energy state analogous to promoting an electron to a higher energy state in atomic spectroscopy the nucleus can then de-excite by y-ray emission 7 is the Greek letter gamma 2 A different nucleus Y may be formed as a result of the nuclear reaction between an incident proton or neutron and the target nucleus X. In most...
Simultaneous Contrast
Included in Aristotle's book On Sense and the Sensible is a description of the three primary ways of mixing colors. One approach is to mix a quantity of one color of paint with a quantity of another color, producing a third, distinctive color of paint, ready to be applied to the painting surface. A second is to place a transparency of one color over an area of another color. In most cases, the transparency is accomplished by adding binder or diluent to the paint to disperse the particles of...
c Scientific Analysis
C-1 L. Bragg, X-ray Crystallography Scientific American, July 1988. C-2 B.D. Cullity, Elements of X-ray Diffraction Addison-Wesley, Reading, Mass., 1978 2nd Edition. C-3 R.E. Dickerson and I.Geis, Chemistry, Matter and the Universe, W.A. Benjamin, Menlo Park, CA., 1976 . C-4 L.C. Feldman and J.W. Mayer, Fundamentals of Surface and Thin Film Analysis, North-Holland, New York, 1986 . C-5 S.J. Fleming, An Evaluation of Physics-Chemical Approaches to Authentication in Authentication in the Visual...
Dendrochronology TreeRing Dating of Panel Paintings
Contributed by PETER IAN KUNIHOLM The Malcolm and Carolyn Wiener Laboratory for Aegean and Near Eastern Dendrochronology Department of the History of Art and Archaeology Cornell University Many European paintings are painted on solid wooden panels or boards, typically oak for Netherlandish paintings. The wood is usually split radially so that, in ideal circumstances, a sequence of annual growth rings from pith to sapwood is present. These sequences are then matched, one against another, by the...
b Varnishes and Refraction
One is between the air and varnish, with An 0.5, and the other is between the varnish and paint, with An 1.1. The varnished paint surface is glossy, and more light is reflected from the varnished surface than from the unvarnished surface, leaving less light to be transmitted to and absorbed by the paint layer. The reflection of light at the paint layer under a coat of varnish is less than that for the unvarnished paint layer because An is smaller at the paint-varnish interface than at the...
Color Light and Space
In the world around us, color appears to be attached to everything we see. It changes as the light changes, but usually within predictable limits, or at least we recognize that a color linked to an object appears a certain way in a certain kind of light. We are conditioned enough by this that we often identify an object by its color. And we are conditioned enough by the change of light to recognize the same object by color even though the condition of light has changed the color of the object....
k Radiocarbon Dating in Art Research
K-1 R.E. Taylor, Radiocarbon Dating An Archaeological Perspective, Academic Press, London, 1987. K-2 M.A. Geyh and H Schleicher, Absolute Age Determination, Springer-Verlag, Berlin, 1990. K-3 R.E.M. Hedges, Nucl. instr. and Meth., B 52, 1990, p. 428. K-4 J.J. Hester, J. Field Archaeol., 14, 1987, p. 445. K-5 R. Gillespie, Radiocarbon User's Handbook, Oxford Committee for Archaeology, Oxford, 1984. K-6 G. Harbottle, E.V. Sayre, and R.W. Stoenner, Application of Science in Examination of Works of...
Pigment Response to Xrays Absorption
In the x-ray portion of the electromagnetic spectrum the wavelengths are around 1 nanometer, a distance nearly one thousand times smaller than wavelengths in the visible spectrum. Consequently, the photon energies are a thousand times greater than the energies of photons in the visible region. In the x-ray region, photon energies are typically in the range of 1,000 to 20,000 electron volts 1 to 20 kiloelectron volts, or keV with an upper level in the range of 100 keV. Above that level, photons...
G Neutron Activation Analysis and Autoradiography
Almost all of neutron activation analysis depends on the relatively high probability that a slow-moving neutron can be captured by an atomic nucleus. This reaction forms a new isotope with a mass number one unit larger than the target atom In this reaction the atomic number Z of the nucleus is unchanged. When the atoms of an element are bombarded by neutrons in a reactor, some of them will absorb a neutron and become radioactive. For example, in the case of sodium, A sodium nucleus with 12...
n Organic Binders Analytical Procedures
N-1 H. Humecki, Ed. , M. Derrick. Infrared Microspectroscopy in the Analysis of Cultural Artifacts, Practical Guide to Infrared Microspectroscopy. New York Marcel Dekker, 1995, 287-322. N-2 S. Halpine. A New Amino Acid Analysis System for Characterizing Small Paint Samples Identification of Egg Tempera and Distemper in a Painting by Cosimo Tura. Studies in Conservation 37 1992 , 22-38. N-3 S. Halpine. An Investigation of Artists' Materials Using Amino Acid Analysis Introduction of the One-Hour...
Introduction Rmn
The word fake has many connotations, including fraud, deception, and forgery. Here, we explore the procedures and methods that can be used to determine whether a painting has been wrongly attributed to a given painter. Forgeries are endemic in the art world. When millions, even tens of millions of dollars, are involved in the purchase of works of art, it is expected that spurious paintings will be represented as authentic works by master painters. The provenance or history of a painting can be...
Paint 1
The paint used by artists to project their ideas and observations can be as simple as a mixture of pigment and binder, with pigment providing the color and the binder joining the particles of pigment together and to the support. A paint may also contain a vehicle that dilutes the pigment binder mixture, allowing the paint to be spread more easily. Other materials may be added to the mixture to enhance the optical or textural characteristics, or to alter the working properties, by accelerating...
Natural Resins
Natural resins are sticky, water-insoluble substances that exude from a wide variety of trees. Most consist of compounds known as terpenoids. The resin that exudes from some types of trees contains copious amounts of natural solvents. One example is pine resin, from which turpentine, a natural solvent is distilled. Resins were known in ancient Egypt, and quite probably earlier. In Egyptian times, they were used in varnishes and figured in mummification procedures, among other uses. A...