pigmented colorants: dependence on media and time - Cornell ...

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Figure 2.9: Pictomicrographs of pigments Egyptian blue, Malachite, and Vermilion. Adapted from [Weh75]. Pigment Volumetric Concentration (PVC): PVC = Pigment Volume (Pigment + Filler + Binder) Volume Further, color is meaningless without longevity. Thus, another important pigment attribute is lightfastness, the ability of the pigment to retain its color unchanged under prolonged exposure to normal conditions of light. This attribute is fundamentally determined by molecular structure, as some molecules degrade or change in continuous presence of light. Permanence refers to a pigment’s chemical stability to any environmental factor, including light, heat, heat, water, acids, al- kalis, or mold. For example, ultramarine blue in extremely lightfast, but will fade on exposure to acids (possibly existing in the support or the air) [Mac05]. These effects are not uniform across all pigments. The most permanent of pigments are inorganic synthetics, and of those that deteriorate, the fastest fading materials are organic. Inorganic pigments that do change, however, do not fade but gray or darken. While is may seem obvious that artists’ paint demands pigments which resist marked change, independent testing and standardized labeling in the USA has only 21
ecome more common recently. The American Society for Testing and Materials (ASTM) developed testing procedures and standards for classifying a pigment’s reaction to light in 1984. The Standard Test Methods for Lightfastness of Colorants Used in Artists’ Materials approximate the color change that can be expected over time in pigments used in artists’ paints in normal indoor exposure [D4384]. The ratings range from I excellent to V very poor. The tests only apply to certain binding materials and a rating for a pigment in one media does not necessarily equate to the same rating in another media. For example, pigments typically last longer inside the protective coatings of oil or acrylic than gum arabic (as in watercolor). For artists, paints should only be considered when they have a ASTM rating of I or II (excellent or very good lightfastness). Under these ratings, the pigment will remain unchanged for 50 to 100 years or more under exposure to light. The most salient pigment attribute for painters is its color. There are many factors inherent in pigments that influence the color of a paint. Color is fundamentally created by the absorption of specific wavelengths of light by electrons oscillating across double chemical bonds in pigments [Mac05]. In addition, color is largely influenced by the particle size, shape and distribution of the pigment. Table 2.1 describes a representative distribution of modern artist’s pigment grades; the smallest of pigments are much larger than a dye molecule, while the largest pigments can be seen by the naked eye. There are many pigment properties determined by particle size, including light scattering properties that are important for artists. The fundamental attribute is the ratio of surface area to volume. Surface area A is of order O(r 2 ), while volume V is of order O(r 3 ) (where r is the radius of a particle). The ratio 22
Page 1 and 2: PIGMENTED COLORANTS: DEPENDENCE ON
Page 3 and 4: ABSTRACT We present a physically ba
Page 5 and 6: Acknowledgements This work would no
Page 7 and 8: Table of Contents 1 Introduction 1
Page 9 and 10: List of Tables 2.1 Average pigment
Page 11 and 12: 3.15 Photoreceptor absorption .....
Page 13 and 14: B.15 Variation of spectral reflecta
Page 15 and 16: corrode the surfaces of materials.
Page 17 and 18: Figure 1.1: Detail of the Azor-Sado
Page 19 and 20: However, since mural artwork is typ
Page 21 and 22: at a very high quality (albeit limi
Page 23 and 24: heterogeneous sum of very different
Page 25 and 26: which linseed oil derives (the most
Page 27 and 28: oration of a rigidly painted layer
Page 29 and 30: ing will hit the ground and reflect
Page 31 and 32: tion of paint tubes in 1841 and the
Page 33: Figure 2.8: Natural pigments of ant
Page 37 and 38: A V = O(r2 ) O(r3 ) = 1 O(r) 24 (2.
Page 39 and 40: Table 2.2: Pigment specific gravity
Page 41 and 42: provide the underlying color to a p
Page 43 and 44: though the speed of light in air is
Page 45 and 46: In general, when light travels from
Page 47 and 48: materials while lit from behind. Li
Page 49 and 50: Table 2.4: Index of refraction η f
Page 51 and 52: to completely congeal. Hence, these
Page 53 and 54: ond together to form proteins. Exam
Page 55 and 56: to its original state by any means.
Page 57 and 58: While it has been used since the 19
Page 59 and 60: organic binder found in more conven
Page 61 and 62: 3.1.1 Visible Light Spectrum Light
Page 63 and 64: Figure 3.2: Hue, brightness and sat
Page 65 and 66: measures how much light is reflecte
Page 67 and 68: Figure 3.6: Additive color mixing o
Page 69 and 70: Figure 3.9: The physical amount of
Page 71 and 72: The vascular tunic lies on the wall
Page 73 and 74: Figure 3.11: Cross section of the r
Page 75 and 76: Not all areas have the same sensiti
Page 77 and 78: identify and distinguish between va
Page 79 and 80: that range between zero and full in
Page 81 and 82: spectrum. This insures that the res
Page 83 and 84: Figure 3.19: Graphical representati
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X x = (X + Y + Z) Y y = (X + Y + Z)
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color into the appropriate RGB colo
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components in the image (the smalle
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haviors of subtractive mixing and i
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of perceptually equal sizes. Unfort
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enabling one to transform between t
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andwidth as converted signals are s
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Figure 3.28: Retinal ganglion recep
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example shown in Figure 3.28. Under
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Figure 3.31: The work of Josef Albe
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sensations for each trial and picke
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Chapter 4 Previous Work There is no
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different location. Subsurface scat
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describes the scattering and absorp
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only accounts for a small percentag
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σ ′ t = σa + σ ′ s and α
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104 Figure 4.4: A model of an alaba
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effects or are too computationally
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108 Figure 4.6: Results using Kubel
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specifying pigments works adequatel
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color representation, it is not fea
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time. A metallic surface patina is
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the system consisted of wetness and
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or darkening enables the museum per
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in front of a displayed work. Felle
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light exposure. This effect is espe
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over time. Perceptually, these hues
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The rate of change of the concentra
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over white grounds) suffer the grea
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protects the deeper remaining color
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light source. This method is used w
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chemical smog and have been identif
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Chapter 5 Preparation & Measurement
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tending transparent pigments used i
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140 Figure 5.1: Spectral reflectanc
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the requirements of the work at han
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144 Figure 5.2: Left: Magnified vie
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Table 5.2: Relevant data regarding
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historically one of the best grades
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created far too strong of a binder,
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too brittle and cracking. While wor
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154 Figure 5.4: Reflectance values
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5.1.5 Painting After the layers of
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The gray card reflected 18% of the
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160 Figure 5.8: The optical setup f
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Note that harmonics reflect at the
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Note that the calibration factors f
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Chapter 6 Experimental Results 6.1
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168 Figure 6.1: Lapis Lazuli in dif
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(such as CIE standards C, D50, orD6
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172 Table 6.2: Perceptual differenc
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174 Figure 6.3: Munsell plots of La
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and j has a saturation of red rsat,
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178 Figure 6.4: Variation of spectr
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visible spectrum are increasing at
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182 Figure 6.5: Munsell plots of La
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trying to match color ca from the p
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as it ages. This is in direct contr
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teractive viewer. In our applicatio
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190 Figure 7.1: Our simulated canva
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where n is the normal at the curren
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In summary, our implementation prov
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Chapter 8 Conclusion We have studie
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inks are beginning to find their wa
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Appendix A Derivation of K-M theory
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∆i − =(K + S) idx 202 ∆j −
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Equation A.8 is now: Rearranging yi
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and if the paint is infinitely thic
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One concatenates the layers into a
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210 Figure B.1: Cold Glauconite in
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Table B.1: Color conversions from t
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214 Figure B.4: Munsell plots of Co
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216 Figure B.5: Burnt Sienna in dif
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Page 233 and 234:
220 Figure B.8: Munsell plots of La
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222 Figure B.9: Red Ochre Tint in d
Page 237 and 238:
Page 239 and 240:
226 Figure B.12: Munsell plots of C
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228 Figure B.13: Variation of spect
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230 Figure B.15: Variation of spect
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Table B.13: Color conversions of Bu
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234 Figure B.18: Munsell plots of C
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236 Figure B.20: Munsell plots of R
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References [Alb71] Josef Albers. In
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240 [GLL + 04] Michael Goesele, Hen
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242 [KM31] Paul Kubelka and Franz M
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[Rat72] Floyd Ratliff. Contour and
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