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

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ceptually appears as adding white to the sample, giving a faded appearance. Sev- eral other pigments experienced similar results, though not all pigments underwent changes during the experiment. In unprotected atmospheres (without the use of activated carbon filters) it would take three (outdoor) to six (indoor) years to accumulate a dose (concentration times magnitude) of ozone exposure from the atmospheric ozone concentrations measured and reported in the work. Pigment size is also a major factor influencing the surface area exposed to the air, which may influence the rate of reaction with the chemical. Similarly, nitrogen dioxide is a common air pollutant formed in the atmosphere from the nitric oxide emissions from fuel combustible sources. Whitmore and Cass found more than half of the natural organic pigment <strong>colorants</strong> studied had a significant color change ∆E >2 from exposure to 0.50 ppm NO2 in air for 12 weeks [WC89]. A dose of this magnitude would be experienced inside an unprotected museum in a few years (2-6 years) in an urban setting. The procedure for the experiment was similar to that of the ozone exposure, mentioned previously. All of these chemical effects are cumulative and irreversible. In relation to the duration of a piece of artwork, these pigment changes occur rather quickly. Care must be taken to protect artwork from such harsh conditions. All in all, the appearance of color of <strong>pigmented</strong> materials in not constant and can be the result of a number of different factors. Through the use of spectropho- tometers, one can accurately measure theses changes over time. Through the use of mathematical predictive color mixing systems, such as Kubelka Munk theory, further changes can be predicted. Hopefully, this knowledge will minimize the risk of further deterioration of artwork for future generations. Equally enticing is the use of the data to travel back in time to see a painting in its original brilliance. 135
Chapter 5 Preparation & Measurement 5.1 Sample creation To study the nonlinear relationship of paint appearance with varying pigments and binding media over time, a number of paint samples were created. Pure pigments were dispersed in a number of different binding media and each applied to a primed piece of canvas. Great care was taken to make sure the samples were of the highest quality. The diffuse reflectance of each sample was measured over the visible spectrum at different intervals in time. 5.1.1 Importance of handmade samples Historically, painters knew their pigments intimately, as they would hand select materials from reliable sources and mix their paints by hand. After the introduction of commercial paint manufacturing, artists were separated from this process and bought tube colors without knowledge of their origin. Further obscuring the origin of their pigments, paint manufacturers sold their colors under confusing and sometimes misleading proprietary names. The practice of documenting the exact 136
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PIGMENTED COLORANTS: DEPENDENCE ON
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ABSTRACT We present a physically ba
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Acknowledgements This work would no
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Table of Contents 1 Introduction 1
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List of Tables 2.1 Average pigment
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3.15 Photoreceptor absorption .....
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B.15 Variation of spectral reflecta
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corrode the surfaces of materials.
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Figure 1.1: Detail of the Azor-Sado
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However, since mural artwork is typ
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at a very high quality (albeit limi
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heterogeneous sum of very different
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which linseed oil derives (the most
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oration of a rigidly painted layer
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ing will hit the ground and reflect
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tion of paint tubes in 1841 and the
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Figure 2.8: Natural pigments of ant
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ecome more common recently. The Ame
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A V = O(r2 ) O(r3 ) = 1 O(r) 24 (2.
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Table 2.2: Pigment specific gravity
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provide the underlying color to a p
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though the speed of light in air is
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In general, when light travels from
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materials while lit from behind. Li
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Table 2.4: Index of refraction η f
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to completely congeal. Hence, these
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ond together to form proteins. Exam
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to its original state by any means.
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While it has been used since the 19
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organic binder found in more conven
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3.1.1 Visible Light Spectrum Light
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Figure 3.2: Hue, brightness and sat
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measures how much light is reflecte
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Figure 3.6: Additive color mixing o
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Figure 3.9: The physical amount of
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The vascular tunic lies on the wall
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Figure 3.11: Cross section of the r
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Not all areas have the same sensiti
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identify and distinguish between va
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that range between zero and full in
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spectrum. This insures that the res
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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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Page 99 and 100: Figure 3.28: Retinal ganglion recep
Page 101 and 102: example shown in Figure 3.28. Under
Page 103 and 104: Figure 3.31: The work of Josef Albe
Page 105 and 106: sensations for each trial and picke
Page 107 and 108: Chapter 4 Previous Work There is no
Page 109 and 110: different location. Subsurface scat
Page 111 and 112: describes the scattering and absorp
Page 113 and 114: only accounts for a small percentag
Page 115 and 116: σ ′ t = σa + σ ′ s and α
Page 117 and 118: 104 Figure 4.4: A model of an alaba
Page 119 and 120: effects or are too computationally
Page 121 and 122: 108 Figure 4.6: Results using Kubel
Page 123 and 124: specifying pigments works adequatel
Page 125 and 126: color representation, it is not fea
Page 127 and 128: time. A metallic surface patina is
Page 129 and 130: the system consisted of wetness and
Page 131 and 132: or darkening enables the museum per
Page 133 and 134: in front of a displayed work. Felle
Page 135 and 136: light exposure. This effect is espe
Page 137 and 138: over time. Perceptually, these hues
Page 139 and 140: The rate of change of the concentra
Page 141 and 142: over white grounds) suffer the grea
Page 143 and 144: protects the deeper remaining color
Page 145 and 146: light source. This method is used w
Page 147: chemical smog and have been identif
Page 151 and 152: tending transparent pigments used i
Page 153 and 154: 140 Figure 5.1: Spectral reflectanc
Page 155 and 156: the requirements of the work at han
Page 157 and 158: 144 Figure 5.2: Left: Magnified vie
Page 159 and 160: Table 5.2: Relevant data regarding
Page 161 and 162: historically one of the best grades
Page 163 and 164: created far too strong of a binder,
Page 165 and 166: too brittle and cracking. While wor
Page 167 and 168: 154 Figure 5.4: Reflectance values
Page 169 and 170: 5.1.5 Painting After the layers of
Page 171 and 172: The gray card reflected 18% of the
Page 173 and 174: 160 Figure 5.8: The optical setup f
Page 175 and 176: Note that harmonics reflect at the
Page 177 and 178: Note that the calibration factors f
Page 179 and 180: Chapter 6 Experimental Results 6.1
Page 181 and 182: 168 Figure 6.1: Lapis Lazuli in dif
Page 183 and 184: (such as CIE standards C, D50, orD6
Page 185 and 186: 172 Table 6.2: Perceptual differenc
Page 187 and 188: 174 Figure 6.3: Munsell plots of La
Page 189 and 190: and j has a saturation of red rsat,
Page 191 and 192: 178 Figure 6.4: Variation of spectr
Page 193 and 194: visible spectrum are increasing at
Page 195 and 196: 182 Figure 6.5: Munsell plots of La
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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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220 Figure B.8: Munsell plots of La
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222 Figure B.9: Red Ochre Tint in d
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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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