[Five Azur Painting]


Table of Contents

[Five Azur Painting]
2017.[December].[06]
2017.[December].[17]



Name: Carl Garris
Date and Time:

2017.[December].[06]

Location: M&K lab
Subject: Testing color of five blue pigments


To recreate and thereby investigate “azur” pigments in BnF Ms. Fr. 640, we prepared paints in walnut oil and glair from the four pigments, including two grades of azurite. For our binding media, we used walnut oil and glair. Glair refers to strained egg white, which requires no special precautions to be taken in the lab. For the oil binding medium, we selected walnut oil because of its use in sixteenth-century Toulousaine paint at the advice of Pamela Smith in November 2017.
In our reconstruction, we manipulated the pigments and binding media used and attempted to keep all other variables constant. We did not think that a control group constituted a feasible option for this study. However, in preparing paints, there are several marks of “equivalence” which we can use in determining what makes two paints “equivalent”: mass/volume ratios, viscosity, and final color. As we are looking at final color for our dependent variable across the board, we cannot use the third option, “final color.” Of viscosity—the ease by which paint adheres to the brush and releases onto the substrate—and mass/volume—the amount of binding media vs pigment—it seems the latter is easier to keep constant. The experiment will be done twice, using mass/volume in one iteration and using viscosity for flow properties in a second iteration.
To attempt to understand the identity of vert dazur and cendres dazur described on 11r, the following text was considered and an experimental test devised with which to investigate it: “Azure ash are only good for landscapes because they die in oil. Only true azure holds on.” (fol. 11r).
The author practitioner provides qualitative properties for “azure ash” here—that it should die (i.e. lose color) in oil, whereas “true azure” should maintain its color. Through preparing the four pigments under consideration in both aqueous and oil media and subsequently analyzing color change, we can procure evidence for the identification of “azure ashes” and “true azure.”
Following the procedures outlined in the entry on 11r, we prepared paints from each of the four pigments under consideration, including two grades of azurite. We created four sets of paints—one set prepared in glair based on mass/volume, a second set prepared in walnut oil based on mass/volume, a third set prepared in glair based on viscosity, and a fourth set prepared in walnut oil based on viscosity. In all cases, we used one gram of the prepared pigment. In the mass/volume controlled paints, we made use of three grams of binding medium. In the viscosity controlled paints, we added indeterminate amounts of binding media (always exceeding three grams) to achieve proper viscosity for painting. We used separate brushes for each pigment and binding media to prevent cross contamination. We used separate plastic droppers to transfer walnut oil and glair likewise to prevent cross contamination. To isolate the pigments in small containers against a white background, we prepared plastic palette cups splitting a commercial plastic artist’s palette.

20171206_garris_azur_01
20171206_garris_azur_02
20171206_garris_azur_03
Image Guide:
The paints painted out onto a mixed media paper. Created by Carl Garris and Tillmann Taape. The columns are: verditer, smalt, lapis lazuli, azurite (unlevigated), azurite (levigated). The rows are: glair by weight, walnut oil by weight, glair by viscosity, walnut oil by viscosity.


Date and Time:

2017.[December].[17]

Location: Columbia University
Subject: Azur Color Analysis


Using photography corrected for white balance using the GIMP GNU Manipulation Program, the RGB values, representing the intensity of red, green, and blue light in each surface respectively on a scale of 0 (none) to 255 (greatest intensity). Using the GIMP GNU Manipulation Program, the average value of a 3-pixel radius circle in the center of each well was taken and tabulated. The results are seen below:


Table 1. The RBG Value of Pigments before and after preparation into paints. In each date point, the first number is the red value on a scale of 0 to 255, the second the green value on a scale of 0 to 255, and the third the blue value on a scale of 0 to 255.

 Verditer Pigment
 Verditer Paint
 Smalt Pigment
 Smalt Paint
 Lapis Lazuli Pigment
 Lapis Lazuli Paint
 Azurite (Unlevigated) Pigment
 Azurite (Unlevigated) Paint
 Azurite (Levigated) Pigment
 Azurite (Levigated) Paint
Mass/Volume Glair
 24.62.176
 9.29.87
 48.56.147
 10.11.36
 85.93.177
 20.29.75
 65.81.143
 25.40.63
 47.62.133
 16.24.61
Mass/Volume Walnut Oil
 24.56.166
 10.29.68
 44.52.138
 7.8.15
 78.89.168
 11.13.35
 63.84.148
 25.32.34
 51.64.136
 24.30.58











Viscosity Glair
 22.58.166
 9.34.102
 42.48.128
 18.20.45
 71.84.159
 19.25.74
 52.66.119
 35.47.60
 53.65.136
 19.31.57
Viscosity Walnut Oil
 24.60.175
 11.27.62
 39.51.130
 2.5.4
 90.101.182
 7.11.20
 56.70.128
 23.30.34
 55.67.138
 10.15.36


Across the table, we can see a decrease in intensity of color following the conversion of pigment into paint. In order to determine which of these transformations constituted a greater loss of color, two separate metrics have been designed. For use in both metrics, the difference between the pigment and paint RGB values have been calculated. Thus, the difference between the Mass/Volume Glair for Verditer is 15.33.89, determine through the following subtraction: 24.62.176 – 9.29.87. The first metric used in determining color change is to sum the RBG values from the difference figure together to determine the total change irrespective of position in red, green, or blue intensity. The second metric used in determining color change attempts to assign a quality value to each value. The quality value is determined through the following method: taking 36.44.94 as the average RGB change across the date collected, the difference of each RGB value from the average is calculated and summed, with values below the average value in the third (blue) position being taken as positive and with values below the average value in the first (red) and second (blue) positions being taken as negative. The reasoning behind this metric is that greater change (i.e. loss) in blue intensity represents a loss of blue color, whereas a greater change in red and green intensities represents a purification of the blue color (the removal of “noise”). Though based on the quantitative RGB values, this second metric is nevertheless subjective as it acts on the assumption that 0.0.255 (pure blue) is an ideal—such a color, unattainable by sixteenth-century means, is here accepted for sake of achieving a usable metric. The results are tabulated below.

Table 2. Delta Values for RGB data, achieved through taking the absolute value of the difference of the pigment and paint values.

 Verditer
Smalt
 Lapis Lazuli
 Azurite (Unlevigated)
 Azurite (Levigated)
Mass/Volume Glair
 15.33.89
 38.45.111
 65.64.102
 40.41.80
 31.38.82
Mass/Volume Walnut Oil
 14.27.98
 37.44.123
 67.76.132
 38.52.114
 27.34.78






Viscosity Glair
 13.24.64
 24.28.83
 52.59.85
 17.19.59
 34.34.79
Viscosity Walnut Oil
 13.33.113
 27.46.126
 83.90.162
 33.40.94
 45.52.102


Table 3. Metric 1: The summed R, G, and B Delta values from Table 2. This metric shows the total change in RGB value irrespective of change type.

 Verditer
Smalt
 Lapis Lazuli
 Azurite (Unlevigated)
 Azurite (Levigated)
Mass/Volume Glair
 137
 194
 231
 161
 151
Mass/Volume Walnut Oil
 139
 204
 275
 204
 139






Viscosity Glair
 101
 135
 196
 95
 147
Viscosity Walnut Oil
 159
 199
 335
 167
 199


Table 4. Metric 2: The quality value of each paint based on the difference from the average Delta, with lower blue values being taken as positive values and lower red/green values being taken as negative values.

 Verditer
Smalt
 Lapis Lazuli
 Azurite (Unlevigated)
 Azurite (Levigated)
Mass/Volume Glair
 -27
 -14
 41
 15
 23
Mass/Volume Walnut Oil
 -43
 -28
 25
 -10
 35






Viscosity Glair
 -13
 -17
 40
 -9
 3
Viscosity Walnut Oil
 -53
 -39
 25
 -7
 9


Based on metric one, the pigment-paint shifts rank in the following order, from least to greatest change: Viscosity Glair Azurite (Unlevigated) (95), Viscosity Glair Verditer (101), Viscosity Glair Smalt (135), Mass/Volume Glair Verditer (137), Mass/Volume Walnut Oil Verditer == Mass/Voume Walnut Oil Azurite (Levigated) (139), Viscosity Glair Azurite (Levigated) (147), Mass/Volume Glair Azurite (Levigated) (151), Viscosity Walnut Oil Verditer (159), Mass/Volume Glair Azurite (Unlevigated) (161), Viscosity Walnut Oil Azurite (Unlevigated) (167), Mass/Volume Smalt (194), Viscosity Glair Lapis Lazuli (196), Viscosity Walnut Oil Smalt ==Viscosity Walnut Oil Azurite (Unlevigated) (199), Mass/Volume Walnut Oil Azurite (Unlevigated) == Mass/Volume Walnut Oil Smalt (204), Mass/Volume Glair Lapis Lazuli (231), Mass/Volume Walnut Oil Lapis Lazuli (275), Viscosity Walnut Oil Lapis Lazuli (335).
Based on metric two, the pigment-paint shifts rank in the following order, from least to greatest quality: Viscosity Walnut Oil Verditer (-53), Mass/Volume Walnut Oil Verditer (-43), Viscosity Walnut Oil Smalt (-39), Mass/Volume Walnut Oil Smalt (-28), Mass/Volume Glair Verditer (-27), Viscosity Glair Smalt (-17), Mass/Volume Glair Smalt (-14), Viscosity Glair Azurite (Unlevigated) (-9), Viscosity Walnut Oil Azurite (Unlevigated) (-7), Viscosity Glair Azurite (Levigated) (3), Viscosity Walnut Oil Azurite (Levigated) (9), Mass/Volume Glair Azurite (Unlevigated) (15), Mass/Volume Glair Azurite (Levigated) (23), Mas/Volume Walnut Oil Lapis Lazuli == Viscosity Walnut Oil Lapis Lazuli (25), Mass/Volume Walnut Oil Azurite (Levigated), Viscosity Glair Lapis Lazuli (40), Mass/Volume Lapis Lazuli Glair (41).
The only pattern consistently identified from metric one is that greater color change occurred through preparing pigment into paint with the walnut oil medium than in the glair medium. While this data perhaps shows us something useful about the nature of oil as a binding medium, it does not help us identify “azure ashes” and “true azur”.
When we consider metric two, we discern an interesting pattern. All pigments perform worse in oil than in glair by a substantial (10) margin, with the exception of Azurite (Levigated) which performs 12 points better in oil than in glair assayed by Mass/Volume (changes in quality between glair and oil for viscosity-assayed Azurite [Levigated] and viscosity-assayed Azurite [Unlevigated] are under 10, and thus not deemed significant. A change of 10 is deemed necessary for significance as 10 was the maximum variation between RGB values taken of the same pigment in the initial photograph). Definitively, verditer and smalt perform quite badly when mixed with binding media, but lapis lazuli and azurite (levigated) perform quite well. However, this metric on its own is deceptive. If it is transformed once more, to show the difference in quality change between the glair vs. walnut oil transformations, the following data are produced:
Table 5. The difference in quality between pigments prepared in glair vs. in walnut oil.

 Verditer
Smalt
 Lapis Lazuli
 Azurite (Unlevigated)
 Azurite (Levigated)
Mass/Volume
 16
 14
 16
 25
 12
Viscosity
 40
 22
 15
 2
 6


Averaging these values between Mass/Volume and Viscosity, we achieve the following data:

 Verditer
Smalt
 Lapis Lazuli
 Azurite (Unlevigated)
 Azurite (Levigated)
Quality Diff. Between Glair and Walnut OIl
 28
 18
 16
 14
 9


Based on these data, it is clear that azurite and lapis lazuli are affected the least by the use of oil as a binding medium instead of glair. Verditer is clearly affected the most. Furthermore, Azurite in particular is separated from verditer by a substantial margin—nineteen points. Might azurite be the “true azure” to which the author practitioner refers, and verditer the “azure ashes”? Such a deduction could make sense considering their respective methods of production.


ASPECTS TO KEEP IN MIND WHEN MAKING FIELD NOTES