Colour Analysis of Unison Pastels

Transcription

1 Colour Analysis of Unison Pastels Paul Centore c February 15, 2014 Abstract Munsell specifications, calculated from spectrophotometric measurements, are presented for Unison Colour s complete line of 422 artist s pastels. The pastels hue, value, and chroma distributions are delineated. Tables and figures are presented, that painters can use in making practical decisions about pastel employment and purchases. A list of duplicates (pairs of pastels whose names are different but whose colours agree to within a CIE DE 2000 value of 2 or less) is given. 1 Introduction A single manufacturer typically produces a few hundred pastels, of various colours. This wide variety is necessary because, unlike paints, pastels cannot be readily mixed to produce large quantities of new colours. The variety, however, requires a significant organizational effort from both artists and manufacturers. The current document helps to provide that organization for one pastel brand, Unison Colour, by analyzing their line of 422 colours. The analysis is performed largely in terms of the Munsell colour system, whose concepts of hue (red, yellow, etc.), value (light vs dark), and chroma (dull vs saturated) are basic to painting. Tables and figures are presented, that should help artists select Unison pastels intelligently, both when painting and when purchasing. Purchasing is especially an issue for online or catalog sales, where the artist cannot see the pastels directly. The Unison gamut is delineated in terms of hue, value, and chroma. Several pairs of duplicates, in which two different pastels produce very similar colours, are also identified. This report first describes the Unison pastel line, and then describes the Munsell system, which will provide rigorous terms of reference for the pastel analysis. The 1

2 PAUL CENTORE analysis procedure and results are given next, including tables and figures for practical use. Finally, an approach is suggested, involving contributions from painters and manufacturers, to extend this analysis to further pastel brands 2 Description of Unison Pastels Unison Colour has divided their complete line of 422 pastels into several series, listed in Table 1. The pastels in each series are numbered for individual reference. For example, Orange 9 is the 9 th pastel in the Orange series. There are five series of earth colours (Brown Earth, Natural Earth, Blue Green Earth, Yellow Green Earth, and Red Earth). Another seven series, that concentrate on certain hues, might be called spectral (Red, Orange, Yellow, Green, Turquoise, Blue Green, and Blue Violet). The Grey, Light, and Dark series are self-descriptive, containing mainly near-neutral colours. Finally, there are some miscellaneous series, containing the Additional, Portrait, and Special Collection series, as well as a series labeled John s Set after John Hersey, Unison s founder. Most of the series contain either 18 or 36 pastels. Typically, a box set contains all the pastels from one or more series. 3 The Munsell System Albert Munsell devised his colour specification system for painters and visual artists. It classifies surface colours by three perceptual attributes that are basic to painting: hue, value and chroma. Hue is universally understood. It says whether a colour is red, yellow, purple, etc. Munsell designates 10 basic hues: R (red), YR (yellow-red, or orange), Y (yellow), GY (green-yellow), G (green), BG (blue-green), B (blue), PB (purple-blue), P (purple), and RP (red-purple). Each basic hue is further subdivided into 4 steps, denoted with a numerical prefix. For example, the four greens are denoted 2.5G, 5G, 7.5G, and 10G. 2.5G is a yellower green, that is closer to GY than it is to BG. 10G is a bluer green, that is closer to BG than it is to GY. In all, then, the Munsell system specifies 40 hues (4 steps for each of the 10 basic hues). These 40 hues are equally spaced perceptually. One could interpolate any desired amount between two adjacent hues. For example, the hue 6GY is a yellowish green that is between 5GY and 7.5GY, but closer to 5GY. White, black, and greys are not considered hues in the Munsell system. Rather, they are designated N, for neutral. Many different colours can have the same hue. Figure 1, for example, shows the hue leaf for 6GY, a set of colours all of which have hue 6GY. The different c 2014 Paul Centore 2

3 COLOUR ANALYSIS OF UNISON PASTELS Series Number of Pastels Additional 62 Blue Green 18 Blue Green Earth 18 Blue Violet 18 Brown Earth 36 Dark 18 Green 36 Grey 36 John s Set 18 Light 18 Natural Earth 18 Orange 18 Portrait 12 Red 18 Red Earth 18 Special Collection 18 Turquoise 6 Yellow 18 Yellow Green Earth 18 Total 422 Table 1: Unison Pastel Series colours within a hue leaf are specified further by value and chroma. The empty boxes indicate colours that are in the Munsell system, but that are beyond the gamut of the process used to produce the figure. The hue leaf shades smoothly into the neutral axis, consisting of greys, shown on the left. Munsell value designates how light or dark a colour is. The theoretically darkest black has a value of 0, and is denoted N0. The theoretically lightest white has a value of 10, and is denoted N10. Between N0 and N10 are 9 progressively lighter greys, denoted N1 through N9. The spacing between the greys is perceptually equal. All colours have a Munsell value, not just the neutrals. For example, there are light blues and dark blues. A blue with value 8.5 has the same lightness as N8.5. Munsell chroma refers to how intense, or saturated, a colour is. For example, a lemon is an intense yellow, while masking tape is a dull yellow. A dull colour is closer to a neutral grey than an intense colour is. The Munsell system denotes 3 c 2014 Paul Centore

4 PAUL CENTORE N9 Chroma Value N8 N7 N6 N5 N4 N3 N2 Hue: 6GY N1 Figure 1: The Hue Leaf for 6GY in the Munsell System chroma numerically. Greys have chroma 0. A colour with a chroma of 10 or higher is generally perceived as saturated. Colours of low chroma, say 4 or less, are perceived as subdued, with a high grey content. The Munsell notation for a colour takes the form H V/C, where H stands for hue, V stands for value, and C stands for chroma. For example, the colour 10R 9/6 would be a very light (V is 9), moderately intense (C is 6), orangish red (H is 10R). A colour with chroma 0 is a neutral grey, which is denoted NV, where V stands for value. For example, N5 is a grey that is midway between white and black. The Munsell system is important to painters for two reasons. First, the attributes it identifies (hue, value, and chroma) are all vital to art. Second, the system provides a language to communicate rigorously about colour. The 1943 Munsell renotation 1 has standardized the calculation of hue, value, and chroma, from objective spectral measurements, so that these terms can be quantified. The standardization was based on a large number of colour judgements made by about 40 human subjects, to insure that Munsell specifications are perceptually meaningful. c 2014 Paul Centore 4

5 COLOUR ANALYSIS OF UNISON PASTELS 4 Analysis 4.1 General Procedure The data set for this analysis consisted of 422 samples, kindly provided by Unison Colour in January 2014, comprising their complete line of pastels. Each sample measured about 3 cm by 4 cm, and had been applied by hand on white paper, in a layer that was opaque (or nearly so). The samples were measured with an X-Rite i1pro2 spectrophotometer, using the M2 setting. The output of a spectrophotometer measurement is a sample s reflectances, at intervals of 10 nm, from 380 to 730 nm. CIE xyy values 2 were calculated for each sample, under the assumption of Illuminant C, which is the illuminant on which the Munsell system is standardized. 1 The 1943 Munsell renotation 1 provides a look-up table from Munsell colours to xyy coordinates. An inversion algorithm 3 was used to find a Munsell specification for each pastel, from its xyy coordinates. Tables 2 through 5 list these Munsell specifications. For researchers who would like to continue these investigations further, the reflectance spectra and the Munsell specifications are available in the computer files UnisonPastelsReflectanceSpectra.txt and MunsellSpecifications- ForUnisonPastels.txt, respectively, at the website centore. Figures 2 through 11 are a sort of inverse to Tables 2 through 5. These figures share the same chroma and value axes that appear in Figure 1. Rather than referring to a single hue, however, each of Figures 2 through 11 refers to a range of hues, which share the same Munsell letter designation. Figure 2, for example, shows all pastels whose hue is between 0R and 10R, so a pastel of hue 3.2R could appear alongside a pastel of hue 9.6R. The pastels in the figures are denoted by obvious abbreviations, given in Table 6. Each pastel in a figure is placed at coordinates given by its chroma and value, as in Figure 1. If multiple pastels with the same hue letter designation (but not necessarily the same numerical hue prefix) also have the same chroma and value, then those pastels are displayed in a sequence, separated by slashes. Painters can use Figures 2 through 11 to determine which Unison pastels have, at least approximately, the desired hue, value, and chroma. Informed choices can then be made when executing a painting. In addition, the figures can aid in purchasing decisions. Typically, colour reproductions in art supply catalogs, either in paper or online, are not accurate enough for confident purchasing decisions, especially given the wide gamut pastels can cover. The figures should provide a better basis for an artists to decide which pastels will be most helpful. 5 c 2014 Paul Centore

6 PAUL CENTORE Brown Earth Natural Earth Blue Green Earth 1 0.9Y 7.8/ YR 3.5/ G 7.8/ Y 7.0/ YR 3.7/ BG 7.2/ Y 6.6/ YR 5.7/ BG 6.3/ YR 5.4/ YR 6.7/ BG 5.8/ YR 3.6/ YR 7.2/ BG 4.7/ YR 2.7/ YR 7.1/ B 2.9/ YR 8.4/ YR 2.8/ G 7.0/ YR 7.4/ YR 3.9/ G 6.4/ YR 6.8/ Y 5.1/ BG 5.2/ YR 6.2/ YR 5.2/ BG 4.8/ YR 4.9/ YR 5.3/ BG 4.1/ YR 3.9/ YR 6.4/ BG 3.5/ YR 7.7/ YR 7.7/ GY 7.9/ YR 7.0/ YR 6.9/ GY 7.1/ YR 6.1/ Y 6.6/ Y 6.1/ YR 5.6/ YR 6.8/ Y 5.2/ YR 4.3/ Y 7.6/ Y 4.0/ YR 3.2/ Y 7.7/ G 3.6/ YR 8.5/ YR 7.5/2.4 Yellow Green Earth Red Earth YR 6.1/ Y 7.9/ R 8.2/ YR 5.2/ GY 7.6/ R 7.5/ R 4.0/ GY 7.0/ R 6.5/ R 3.0/ G 6.2/ R 5.6/ Y 7.9/ G 5.4/ R 4.9/ YR 7.4/ G 4.5/ R 2.9/ Y 5.9/ Y 7.9/ YR 7.8/ YR 4.9/ Y 7.3/ R 7.0/ YR 4.2/ GY 6.8/ YR 6.0/ YR 3.6/ Y 5.6/ R 5.2/ Y 8.3/ Y 4.9/ YR 4.0/ Y 7.1/ Y 4.6/ R 3.4/ Y 5.7/ Y 8.2/ YR 8.3/ Y 5.0/ Y 7.6/ YR 7.3/ Y 3.8/ Y 7.0/ YR 5.7/ Y 3.1/ Y 5.9/ R 4.8/ Y 4.8/ YR 3.9/ GY 3.8/ YR 3.2/5.5 Table 2: Munsell Specifications for Unison Earth SeriesPastels c 2014 Paul Centore 6

7 COLOUR ANALYSIS OF UNISON PASTELS Green Red Orange Yellow 1 9.5G 3.4/ R 3.6/ R 4.8/ YR 5.2/ G 4.5/ R 4.7/ R 5.0/ Y 6.4/ G 5.4/ R 5.9/ R 6.0/ Y 6.9/ GY 6.7/ YR 6.3/ R 6.3/ Y 8.4/ GY 7.5/ R 6.9/ R 6.5/ Y 8.9/ GY 8.2/ R 7.3/ R 7.9/ Y 9.1/ G 4.1/ R 3.2/ YR 6.1/ YR 6.6/ G 4.6/ R 3.5/ YR 6.7/ YR 7.3/ G 5.6/ R 5.1/ YR 7.1/ Y 7.6/ GY 5.9/ R 5.8/ YR 7.5/ Y 8.5/ GY 7.3/ R 6.8/ YR 8.0/ Y 8.8/ GY 8.2/ R 7.4/ YR 8.4/ Y 9.0/ G 3.2/ R 2.9/ YR 6.7/ YR 5.7/ GY 4.2/ RP 3.1/ YR 7.4/ YR 6.5/ GY 5.0/ RP 3.9/ YR 7.7/ YR 6.9/ GY 5.8/ RP 5.4/ YR 7.9/ Y 7.3/ GY 7.3/ RP 6.5/ YR 8.3/ Y 8.3/ Y 8.1/ RP 7.4/ YR 8.6/ Y 8.8/ BG 4.0/ G 5.3/6.1 Turquoise Blue Green Blue Violet G 5.9/ BG 4.5/ B 3.2/ P 8.4/ G 6.9/ B 4.9/ PB 4.2/ P 7.5/ G 7.6/ BG 5.6/ PB 5.8/ P 6.9/ G 8.1/ B 6.2/ B 7.2/ PB 6.0/ G 4.2/ B 7.3/ B 7.8/ P 4.1/ GY 5.4/ B 7.8/ B 8.7/ P 3.3/ GY 6.3/ B 4.1/ PB 8.6/ GY 7.1/ B 5.0/ PB 8.0/ GY 7.6/ B 6.4/ PB 7.0/ GY 8.4/ B 7.3/ PB 5.9/ GY 4.4/ B 7.9/ PB 4.8/ GY 5.1/ B 8.5/ PB 4.4/ GY 6.1/ B 4.0/ B 7.8/ GY 7.6/ B 4.6/ PB 7.0/ GY 8.5/ B 5.8/ PB 6.0/ GY 8.9/ B 7.3/ PB 4.7/ BG 7.9/ PB 3.8/ G 8.5/ PB 2.7/6.8 Table 3: Munsell Specifications for Unison Spectral Pastels 7 c 2014 Paul Centore

8 PAUL CENTORE Grey Dark 1 5.1Y 3.8/ YR 3.1/ BG 4.8/ R 2.7/ GY 6.2/ YR 2.7/ BG 6.6/ YR 3.1/ G 7.2/ Y 2.9/ Y 8.2/ Y 3.6/ P 4.1/ BG 2.7/ PB 5.2/ BG 2.8/ PB 6.2/ G 3.8/ PB 7.4/ G 3.4/ PB 7.9/ GY 3.8/ G 8.2/ GY 3.8/ Y 2.2/ PB 2.7/ B 3.5/ P 3.3/ PB 5.3/ B 2.5/ PB 6.5/ B 1.9/ Y 7.8/ PB 2.7/ Y 8.5/ PB 2.0/ Y 5.5/ Y 5.8/5.6 Light Y 6.7/ YR 9.4/ Y 7.6/ Y 9.2/ Y 8.3/ Y 9.2/ Y 8.7/ YR 9.1/ Y 8.7/ YR 8.9/ Y 9.2/ R 8.7/ Y 9.3/ R 8.8/ Y 9.4/ R 8.4/ GY 8.7/ R 8.1/ GY 8.2/ RP 8.6/ G 7.9/ RP 9.0/ BG 6.8/ RP 9.1/ B 6.2/ P 8.6/ B 4.8/ PB 8.9/ B 3.4/ BG 8.8/ B 2.1/ BG 9.2/ G 9.1/ G 9.0/1.1 Table 4: Munsell Specifications for Unison Grey, Dark, and Light Pastels c 2014 Paul Centore 8

9 COLOUR ANALYSIS OF UNISON PASTELS Additional (1-38) Additional (39-62) Special Collection 1 4.5PB 8.6/ Y 4.3/ YR 6.1/ B 8.4/ Y 5.7/ YR 6.6/ BG 8.4/ Y 7.2/ YR 5.3/ P 8.2/ Y 8.1/ YR 4.8/ RP 8.0/ BG 2.7/ R 4.4/ RP 7.2/ G 4.0/ R 4.3/ Y 9.1/ G 5.1/ R 3.5/ Y 8.9/ G 6.2/ RP 3.7/ Y 8.2/ GY 7.5/ RP 2.8/ Y 9.1/ G 8.0/ P 4.3/ Y 8.8/ B 1.9/ P 3.7/ Y 8.4/ PB 2.4/ PB 4.4/ YR 7.0/ B 3.7/ PB 4.8/ R 5.7/ B 5.2/ B 3.8/ R 4.6/ B 7.1/ B 4.1/ YR 5.5/ B 8.1/ BG 3.9/ R 5.8/ RP 5.7/ GY 3.5/ R 5.6/ RP 5.8/ Y 3.4/ YR 7.9/ P 5.2/ YR 7.3/ RP 4.2/3.5 John s Set YR 6.6/ P 6.6/ R 3.9/ YR 4.9/ P 6.2/ R 5.1/ YR 3.9/ PB 6.3/ R 5.1/ YR 2.9/ PB 6.3/ R 5.8/ YR 7.7/ YR 6.9/ YR 6.7/0.7 Portrait 6 7.8YR 8.1/ YR 5.1/ YR 7.7/ R 5.1/ R 3.9/ YR 7.9/ RP 5.3/ RP 3.0/ YR 7.7/ PB 5.8/ P 2.6/ YR 8.1/ PB 5.8/ P 8.1/ YR 8.4/ PB 7.1/ P 7.4/ R 5.0/ PB 7.8/ P 6.6/ R 4.5/ G 6.5/ P 5.1/ R 3.1/ B 5.9/ P 4.2/ RP 3.8/ B 3.9/ RP 3.4/ RP 6.7/ BG 6.1/ GY 2.5/ RP 7.6/ G 5.5/ Y 3.4/ R 6.9/ B 5.8/5.4 Table 5: Munsell Specifications for Remaining Unison Pastels 9 c 2014 Paul Centore

10 PAUL CENTORE Abbreviation Unison Series Name A Additional BE Brown Earth BG Blue Green BGE Blue Green Earth BV Blue Violet G Green J John s Set NE Natural Earth O Orange Port Portrait R Red RE Red Earth SC Special Collection T Turquoise Y Yellow YGE Yellow Green Earth Table 6: Abbreviations in Figures 2 through 11 c 2014 Paul Centore 10

11 COLOUR ANALYSIS OF UNISON PASTELS 9 8 Light7 Light6 Light8 RE1 Light9 O6 RE2 BE8/BE26 R12 R6 7 RE8 Port12 R11 R5 Munsell Value 6 5 RE3 RE4 RE5 RE16 A18 RE10 J7 J2/J3 Port6 SC5 O5 O4 R3 A17/R10/J4 R9 O1 R2 Port7 SC6 A15 O3 O2 A14 4 A28 BE23 J1 3 BE24 Dark2 RE6 R13 RE12 Port8 SC7 R1 R7 R Munsell Chroma Figure 2: Unison Pastels of Munsell Hue R 11 c 2014 Paul Centore

12 PAUL CENTORE Light1 9 Light4 Light5 Munsell Value O18 BE19 BE7 P5/O12 RE13 A19 RE7 A25 BE13 NE13 Port1 BE20 A20 NE16 A26 A21 BE21 BE26/BE8 RE14 NE5 NE6 BE14 NE14 BE9 NE4 NE12 BE10 BE15 RE9 RE15/NE3 BE16 BE4 NE11 BE22/NE10 A27 A22 BE28 BE11 O17 Port4 O11 Port2 Port3 J6 O16 O10 Y15 Y14 R4 Y13 SC3 Y1 SC4 O15 Y8 J5 A16 O9 Y7/SC2 O13 O14 A13 O8 SC1/O7 4 BE17 BE29 A23 NE8 BE5 NE2 BE30 BE12/RE17 NE1 RE11 3 BE18 Dark4 Dark1 A24 NE7 BE6/Dark3 RE Munsell Chroma Figure 3: Unison Pastels of Munsell Hue YR c 2014 Paul Centore 12

13 COLOUR ANALYSIS OF UNISON PASTELS 9 8 Grey28 Grey26 Grey27 Light2/Light3 A7 Y6 Y12 A8 Y5 Y18 Grey25/Grey24 Grey18 BE31 Grey23 Y17 Grey6 YGE13 A42 G18 Grey17 YGE1 BE1 BE25 NE17 NE18 YGE14 Grey22 Y11 YGE7 Y4 A10 A11 Y10 A9 Y9 A12 7 A41 BE32 BE2 YGE15 Grey21 YGE8 Y16 Y3 Y2 Munsell Value 6 5 BGE15 A40 BE33 BGE16 NE9 BE34 YGE17 BE27/YGE16 Grey20 Grey19 YGE11 YGE12 YGE10 4 A39 BGE17 Grey1 BE35 Dark6 A38 SC18 NE15/BE3 3 Dark5 BE36 2 Grey Munsell Chroma Figure 4: Unison Pastels of Munsell Hue Y 13 c 2014 Paul Centore

14 PAUL CENTORE 9 8 Grey29 Grey30 G6 BGE13 G36 G12 G35 G30 7 A47 YGE2 G5 BGE14 YGE3 G4 G17 YGE9 G11 G34 G28 G29 Munsell Value 6 5 Grey3 G16 G32 G15 G10 G33 G26 G27 4 SC17 YGE18 G14 G31 Dark12/Dark11 3 A Munsell Chroma Figure 5: Unison Pastels of Munsell Hue GY c 2014 Paul Centore 14

15 COLOUR ANALYSIS OF UNISON PASTELS 9 Light17 Light18 BG18 8 Grey12 A48 Grey31 BGE1 G24 G23 7 Grey5 BGE7 G22 Munsell Value 6 5 J13 BGE8 A46 YGE4 J17 YGE5G3 A45 G21 G9 G20 YGE6 G2 G8 4 3 A44 Dark9 BGE18 G13 Dark10/G1 G25 G Munsell Chroma Figure 6: Unison Pastels of Munsell Hue G 15 c 2014 Paul Centore

16 PAUL CENTORE 9 Light16 Light15 A3 8 BG17 7 Grey4 BGE2 Grey32 BGE3 Munsell Value 6 5 Grey2 J16 BGE4 BGE9 BGE10 BGE5 T1 T3 4 BGE11 SC16 G19 BGE12 3 Dark8 A43/Dark Munsell Chroma Figure 7: Unison Pastels of Munsell Hue BG c 2014 Paul Centore 16

17 COLOUR ANALYSIS OF UNISON PASTELS 9 BG6 BG12 A2 8 A54 BV13 BG11 BG5 T6 7 A53 BG16 BG10/T5 BG4 BG9 Munsell Value 6 5 Grey34 Grey33 A52 J14 J18 T4 BG15 T2 BG14 BG8 4 3 Grey14 Grey35 J15 A51 BGE6 SC15 BG1 BG13 SC14 BG7 Dark15 2 Grey36 A49/Dark Munsell Chroma Figure 8: Unison Pastels of Munsell Hue B 17 c 2014 Paul Centore

18 PAUL CENTORE 9 Light14 A1/BV7 8 Grey11 BV8 J12 Grey10 7 BV14 J11 BV9 Grey16 Munsell Value 6 5 Grey15 Grey8 Grey9 BV15 BV16 J9 A61 A62 BV4 J10 BG3 BV10 SC13 BV11 4 BV17 BG2 SC12 BV12 3 Dark17 Dark13 BV18 A50 2 Dark Munsell Chroma Figure 9: Unison Pastels of Munsell Hue PB c 2014 Paul Centore 18

19 COLOUR ANALYSIS OF UNISON PASTELS 9 8 Light13 BV1 A4 A31 A32 BV2 7 BV3 A33 A59 Munsell Value 6 5 A57 A34 A60 4 A35 Grey7 SC10 BV5 SC11 3 Dark14 BV6 A Munsell Chroma Figure 10: Unison Pastels of Munsell Hue P 19 c 2014 Paul Centore

20 PAUL CENTORE 9 Light12 Light11 Light10 8 A5 Port11 R18 7 A6 Port10 R17 Munsell Value 6 5 A56 A55 J8 R16 4 A58 SC8 Port9 R15 A36 3 A29 SC9 R Munsell Chroma Figure 11: Unison Pastels of Munsell Hue RP c 2014 Paul Centore 20

21 COLOUR ANALYSIS OF UNISON PASTELS 4.2 Hue, Value, and Chroma Distributions Figures 12 through 14 are histograms of the entire Unison line in terms of hue, value, and chroma. Figure 12 shows that the Unison pastels cover the entire gamut of hues, though not evenly. There are about twice as many pastels in the hues between 5R and 5Y, as there are in the rest of the hues. Human skin tones mainly cluster between 5R and 5Y, so this predominance would provide fine colour distinctions for portrait or figure painting. Figure 13 gives the overall Munsell value distribution of the pastels. The bulk of the pastels fall fairly evenly between values 2.5 and 9.5. There are relatively few very dark or very light pastels. Tables 7 and 8 list the five darkest and five lightest pastels. The darkest pastels tend, not surprisingly, towards neutrality, and have Munsell values near 2. This minimum should be compared with oil or acrylic paints, in which the darkest blacks tend to have values near 1, a full value step darker than the darkest Unison pastels. The lightest pastels also tend towards neutrality, and also do not reach the extremes routinely achieved by oil and acrylic paints. Titanium white, for example, which is the standard artist s white today, has a value of about 9.8, while the lightest Unison pastels only reach 9.4, about half a value step lower. In general, then, Unison pastels have a restricted value range, when compared to paints. Pastel Munsell Specification Munsell Value Dark B 1.9/ Additional B 1.9/ Dark PB 2.0/ Grey B 2.1/ Grey Y 2.2/ Table 7: Darkest Unison Pastels Figure 14 is a histogram of the chromas of Unison pastels. The chromas peak at just over 2, and taper off steadily, reaching a maximum around 16. Very intense colours, with chromas of 10 or above, attract attention, so most artists tend to use them sparingly, as accents. The bulk of the colours in a painting are usually of low or moderate chroma, so the Unison pastel line fits this pattern. Tables 9 and 10 list the five least and five most saturated Unison pastels. The pastels in Table 9 all have chromas of 0.5 or less, so they are very neutral greys. Not surprisingly, they all belong to the Grey series. The very intense pastels in Table 10 all have similar hues, clustering around reddish orange. Their values are also similar, around 6 or 21 c 2014 Paul Centore

22 PAUL CENTORE Pastel Munsell Specification Munsell Value Light 1 9.1YR 9.4/ Grey Y 9.4/ Grey Y 9.3/ Light BG 9.2/ Light 3 4.6Y 9.2/ Table 8: Lightest Unison Pastels Figure 12: Hue Histogram of Unison Pastels c 2014 Paul Centore 22

23 COLOUR ANALYSIS OF UNISON PASTELS Number of Pastels Munsell Value Figure 13: Value Histogram of Unison Pastels Number of Pastels Munsell Chroma Figure 14: Chroma Histogram of Unison Pastels 23 c 2014 Paul Centore

24 PAUL CENTORE Pastel Munsell Specification Munsell Chroma Grey Y 7.8/ Grey Y 8.5/ Grey B 2.1/ Grey PB 6.5/ Grey Y 9.4/ Table 9: Least Saturated Unison Pastels Pastel Munsell Specification Munsell Chroma Additional YR 7.0/ Additional R 5.7/ Orange 7 1.8YR 6.1/ Orange YR 7.4/ Orange 8 3.8YR 6.7/ Table 10: Most Saturated Unison Pastels 7, so there is not much variety in the highly saturated pastels. 18 of the top 20 most saturated pastels, in fact, are in the mid-valued, warm part of the spectrum, clustering near orange. The other two, Blue Violet 12 and Blue Violet 11, have chromas of 14.8 and 13.2 respectively, and have a purplish-blue hue. 4.3 Duplicates In addition to Munsell characteristics, colour differences between pastels were also analyzed. The CIE DE 2000 difference formula, 2,4 commonly abbreviated E 00, was used. This formula depends on an illuminant, so Illuminant C, which is specified in the Munsell renotation standard, was used in calculations. The lower the E 00, the more similar two colours are. When the E 00 of two colours is low enough, even if it is not 0, the two colours are indistinguishable. It is not always clear how low E 00 should be for indistinguishability, but a cutoff of 2 was used for this analysis. E 00 values were calculated for every possible pair of Unison pastels. Table 11 shows all pairs, 18 in total, whose E 00 was 2 or less. A painter can verify for himself that these pairs are duplicates (or nearly so), by applying the two pastels in a pair, in thick layers, adjacent to each other. It will usually be difficult to tell where one colour stops and the other colour starts. From a practical point of view, a painter would not need to purchase one of the pastels in each pair. The manufacturer could similarly replace one of the pastels in each pair with a brand c 2014 Paul Centore 24

25 COLOUR ANALYSIS OF UNISON PASTELS First Pastel Second Pastel Difference ( E 00 ) Dark 16 Additional Natural Earth 15 Brown Earth Blue Violet 7 Additional Yellow Green Earth 4 Grey Natural Earth 14 Brown Earth Orange 11 Portrait Orange 11 Portrait Grey 28 Light Light 2 Light Portrait 6 John s Set Portrait 2 Portrait Natural Earth 18 Brown Earth Natural Earth 18 Brown Earth Orange 16 John s Set Additional 17 John s Set Natural Earth 17 Brown Earth Grey 31 Additional Light 2 Additional Table 11: Duplicate Pairs of Unison Pastels new colour, thus extending the line s gamut without increasing the number of pastels produced. 5 Other Pastel Brands The current document has analyzed only one pastel manufacturer, Unison. Comparative studies, involving other manufacturers, would be even more helpful to pastel artists. The calculations, including the production of the histograms and plots in this document, have been largely automated, using code written for Octave or Matlab. The measurements are straightforward and reasonably quick, once samples are available. A sample in this context is just a piece of paper to which the pastel has been applied, rather than the pastel itself. The current bottleneck is obtaining samples. While the author owns several hundred pastels from many brands, he has no complete line from any one brand. Other pastel artists, who do have complete sets, are invited to contribute to further 25 c 2014 Paul Centore

26 PAUL CENTORE pastel analysis by sending the author samples, which he can measure and analyze. The samples should meet the following conditions: 1. The area of each sample should be at least one square inch (or 6 square centimeters), 2. The samples should be applied to a standard pastel paper. White Canson Mi-Teintes paper is adequate, but sanded papers, such as Wallis or Sennelier LaCarte, work well, too, 3. The pastels should be applied thickly enough that the samples are opaque. When in doubt, add more pastel to a sample. Ideally, it should be impossible to discern the colour of the paper through the pastel sample, 4. The surface of the samples should be reasonably smooth, with no obvious irregularities. Rubbing the pastel with a finger produces a sufficient finish, 5. The samples should be clearly labelled, using the pastel manufacturer s naming convention, 6. Do not use any fixative, as this can alter colours. A protective sheet of Glassine can be used over each sheet of samples, to keep the pastel from rubbing off, and 7. There is no problem using a large number of smaller sheets (say 8.5 by 11 inches), for easier shipping. Once the samples are prepared, they can be mailed to the author, Paul Centore, at 62 Chicago Ave., Groton, Connecticut 06340, USA, who will measure them, and prepare a report, similar to this one, that he will post on his website. Artists should be aware that preparing samples can be considerably more time-consuming and tedious than it seems, especially since it is important to produce a thick, opaque layer. An entire set of samples can take eight hours or more, depending on the number of pastels. Apart from artists, pastel manufacturers are also invited to send samples of their lines. If the preparation process is too tedious, then the manufacturer can send a complete set of pastels to the author, who will prepare the samples himself, and generate a report. In addition to providing some exposure, the report might also be helpful at identifying unexpected duplicates, or gaps in gamut coverage, that can be used for revision and development of the pastel line. References 1. Sidney Newhall, Dorothy Nickerson, & Deane B. Judd. Final Report of the O. S. A. Subcommittee on the Spacing of the Munsell Colors, JOSA, Vol. 33, Issue c 2014 Paul Centore 26

27 COLOUR ANALYSIS OF UNISON PASTELS 7, 1943, pp CIE. Colorimetry. Vienna: CIE Technical Report No. 15:2004, 3 rd ed., Central Bureau of the CIE; Paul Centore, An Open-Source Inversion Algorithm for the Munsell Renotation, Color Research & Application, Vol. 37, No. 6, December 2012, pp Gaurav Sharma, Wencheng Wu, & Edul N. Dalal, The CIEDE2000 Formula: Implementation Notes, Supplementary Test Data, and Mathematical Observations, COLOR Research and Application, Vol. 30, Number 1, February 2005, pp c 2014 Paul Centore