Pigment

Pigment imparts color to other materials. In paint, the pigment is a powdered substance which, when mixed in the liquid vehicle, imparts color to a painted surface.

The pigments used in paints are nearly all metallic compounds, but organic compounds are also used.

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Most black pigments are organic, e.g., bone black (animal black or charcoal) and lampblack.

Some of the metallic pigments occur naturally. The brilliant and beautiful coloring of the rock and soil in some parts of the United States, especially in the Grand Canyon of the Colorado River, the Painted Desert of Arizona, and Bryce and Zion canyons of Utah, is largely produced by such compounds, chiefly oxides.

Yellow ocher, sienna, and umber are oxides of iron. Litharge is a yellow oxide of lead. Red lead is also an oxide of this metal. Lead chromate, or chrome yellow, is an important yellow pigment. White lead, or basic lead carbonate, is a pigment long in use; it is rendered more durable by mixture with zinc oxide. Cadmium yellow is a sulfide of cadmium. Ultramarine is an important blue pigment, as is Prussian blue (ferric ferrocyanide). Green pigment is produced by mixing Prussian blue and chrome yellow. Vermilion (mercuric sulfide) is red. Pigments occur in plant and animal bodies. The bright colors of plants, for example, are the result of the presence of such substances as chlorophyll (green) and xanthophyll (yellow), both of which are also found in some animals. Among others are carotene, the yellow of carrots and certain other vegetables, and anthocyanin, which imparts blue, red, and purple to flowers. Blood receives its color from the hemoglobin in the red corpuscles. Coloration of human skin is caused by the presence of pigments

 

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Fugitive pigments

In painting, are non-permanent pigments (pigments that lighten in what is understood to be a relatively short time when exposed to light).

While most paintings are supposed to be done with permanent pigments, painters have made work wholly or partially with fugitive pigments for a number of reasons: ignorance as to the permanence of the pigments, prioritizing the appearance of the colors one can get with fugitive pigments over permanence, or the desire to have a painting change in appearance over time.

"Paintings fade like flowers", wrote Vincent to his brother Theo, and "All the colors that Impressionism has brought into fashion are unstable, so there is all the more reason to simply use them too brightly -  time will tone them down only too much".

These are just two passages from the letters that reveal that, like other painters of his day, Van Gogh was all too aware of the transient nature of certain colors that he used.

One of the most vulnerable colors is red lake, an organic pigment that can fade considerably under the influence of light. Changes in color varied significantly, depending on factors such as the type of red pigment used, how the pigment was made and how the artist applied this. The presentation examines this phenomenon with the aid of four of Van Gogh's Paris works. Scientific analysis has shown that the artist used a different kind of red lake in each of these paintings.

A broad interdisciplinary study was set up to gain understanding of how and why red lake paints deteriorate in paintings by Van Gogh and his contemporaries.

 

Mark Rothko

Rothko regarded his floating rectangles of color as objects, not as actions or color fields....vehicles for expressing emotion.

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A rare quality of light appears to radiate from a mysterious source within the canvas center. This seemingly magical effect was achieved by the optical illusion of pure areas of color set side by side and Rothko's painterly handling of the canvas edges, which were brushed into the adjoining field. This slight nuance of color contrast seems to cause a slight visual vibration to occur around the edges, creating the eerie sense of a glowing light from within. 

The Harvard Series

Originally hung in the dining room of Harvard's Holyoke Center in 1963 per deed of gift from the artist, the murals had suffered from tears, stains, graffiti, and severe color shifts caused by exposure to sunlight and instability in the artist's materials.

Rothko's estate has been sued repeatedly for his use impermanent colors in his works and many other artists are embroiled in lawsuits regarding shoddy craftsmanship.

Although Rothko has the reputation of being a poor technician, it is striking that he attempted a number of the thoroughly traditional materials and techniques, notably the grinding of his own pigments and the use of a variety of egg tempera (he adopted the late medieval technique of interposing an isolating egg-white glaze between layers of pigments or vanish,  unfortunately, egg white becomes very brittle with time and turns brown).

 

Seurat's Pigments

Georges Seurat first employed his “chromo-luminist” painting technique on A Sunday on La Grande Jatte – 1884 beginning in late 1885. Painting with small brushstrokes of pigments that were minimally mixed on the palette, he aimed to impart luminosity to the surface and to explore 19th century ideas of color theory, such as simultaneous contrast.

Pigment analysis has disclosed that the dots and dashes containing zinc yellow have darkened significantly: yellow, green-yellow, and orange brushstrokes have become dark yellow, olive-green, and reddish brown, respectively.

Additionally, the painting has further darkened due to the natural aging of the linseed oil medium.

By performing spectral reflectance measurements on darkened areas of the painting and on paint-outs of fresh unaltered colors, imaging the painting with color-managed digital photography, and image editing with Photoshop, a digital version of the original, more luminous appearance of La Grande Jatte was simulated.

 

1. INTRODUCTION

One of the most famous neo-impressionist paintings exemplifying pointillism is Georges Seurat’s A Sunday on La Grande Jatte – 1884, part of the permanent collection of the Art Institute of Chicago, and the subject of a major exhibition in 2004 including several scientific examinations.1

One of the examinations including pigment analysis and digital rejuvenation of a color-managed image of the painting.

A team was formed consisting of color and imaging scientists from the Munsell Color Science Laboratory, and from the Art Institute, painting conservators, conservation scientists, and photographers. We also worked closely with the curatorial staff. Through this collaboration, we were able to successfully create a CIELAB image and a full-size print of the painting suggesting its appearance during its first public display in May1886, at the Eighth and last Impressionist exhibition in Paris. (Strictly speaking, this predates the painted border added sometime in 1888-1889.)

2. SUMMARY OF METHODOLOGY

In-situ spectral reflectance measurements were made using a Gretag-Macbeth EyeOne and SpectroEye visible spectrophotometers of brushstrokes containing zinc yellow and a range of colors.

Many of the dots and dashes were also sampled to determine specific pigment composition. The spectral data ranged between 0.041 and 0.664 (reflectance factor), constrained by the fairly coarse canvas support and the aged medium.

A Jenoptik Eyelike Precision M11 digital camera and four Hensel Xenon strobes were used to image the painting. Two test targets were also measured spectrally and imaged, the GretagMacbeth ColorChecker DC (CCDC) and a custom target made using Gamblin Conservation Colors. A camera profile was created using the CCDC, relating digital signals to CIELAB coordinates. The average performance for the CCDC and Gamblin targets was 1.9ΔE00 and 2.4ΔE00, respectively.

The first step of the digital rejuvenation involved correcting for natural aging of the painting, which includes the yellowing of the linseed oil, the increased transparency of the lead white and the presence of the underlying paint and ground layers. Using the Kubelka-Munk theory, an “aging spectrum” was calculated; an area of pure aged lead white on the painting — the sailboat in the upper left — was used to determine a spectrum that when subtracted from the in-situ measurement would yield the same lightness as un-aged lead white. (All spectral calculations described in this summary used single-constant Kubelka-Munk theory.) CIELAB coordinates were plotted for both sets of spectra revealing monotonic behavior that was modeled empirically. These equations were used to create Photoshop custom Curves. La Grande Jatte could be un-aged by applying these sets of Curves.

Fresh paint outs of lead white, zinc yellow, emerald green, and vermilion dispersed in linseed oil and applied to a white board were prepared and measured spectrally. These were used as a reference for the unaltered colors and approximated the original colors used by Seurat. Because of differences in opacity between these paint outs and the painting, the spectra were adjusted by blending each with the spectrum of the underlying paint layers in either a 3:1 or 1:1 ratio.

In order to un-darken the zinc yellow, its tinting strength had to be estimated. Changes in tinting strength (or concentration) change the amount of light absorption. Below 470 nm, the amount of reflectance was due to absorptions by the yellow pigment and ageing. This principle enabled the estimation of the strength of Seurat’s zinc yellow. The fresh zinc yellow was scaled so that its spectrum when added to the ageing spectrum most closely matched the average in-situ yellow spectrum between 380 and 470 nm. A similar approach was used to un-darken brushstrokes containing zinc yellow mixed with either emerald green or vermilion.

Using Photoshop’s Magic Wand editing tool, darkened yellow, green-yellow, and orange dots were selected across the painting. For each color, there was a range of CIELAB coordinates, resulting from differences in pigment concentrations, thickness, and opacity. Assuming this range was invariant with color, translating their coordinates from darkened to un-darkened values would yield a realistic rendering, that is, retain their natural variability. Photoshop custom Curves were created to implement each translation. Following the un-darkening, the image was un-aged. The translational approach produced reasonable results. The digitally rejuvenated painting clearly possesses luminosity. The contrast is increased and the complementary haloes are much more visible, resulting in a greater sense of depth. In the sunlit grass, the dark holes now are points of colored specular highlights.

3. RESULTS

The following are images of La Grande Jatte before and after digital rejuvenation.

If we assume that the digital rejuvenation is a reasonable approximation to how the painting looked in 1889, we observe the increase in luminosity. The figures frozen in time are more distinct from the background. There is a greater sense of depth. The complementary haloes around many of the figures are more observable, further increasing their luminosity via simultaneous color contrast.

The area to the left of the little girl, seen in Figure 3, has been a topic of discussion among art historians because of its smudged appearance compared to the rest of the sunlit grass. Following digital rejuvenation, this area no longer stands out. The darkened dots and dashes made this region more noticeable, an effect not intended by Seurat.

Figure 4 depicts an example of how the figures are more distinct from the background grass.

 

 

Tattoos

What Are Tattoo Inks? ..........You can't be 100% certain!

 

Manufacturers of inks and pigments are not required to reveal the contents. A professional who mixes his or her own inks from dry pigments will be most likely to know the composition of the inks. However, the information is proprietary (trade secrets), so you may or may not get answers to questions.

Most tattoo inks are composed of pigments that are suspended in a carrier solution. Contrary to popular belief, pigments usually are not vegetable dyes. Today's pigments primarily are metal salts. However, some pigments are plastics and there are probably some vegetable dyes too. The pigment provides the color of the tattoo. The purpose of the carrier is to disinfect the pigment suspension, keep it evenly mixed, and provide for ease of application.

Tattoos and Toxicity

However, there are important health risks associated with tattooing, both from the inherent toxicity of some of the substances involved and unhygienic practices. Pigments and tattoo inks are not regulated by the US Food and Drug Administration.

Pigment Chemistry

The oldest pigments came from using ground up minerals and carbon black. Today's pigments include the original mineral pigments, modern industrial organic pigments, a few vegetable-based pigments, and some plastic-based pigments. Allergic reactions, scarring, phototoxic reactions (i.e., reaction from exposure to light, especially sunlight), and other adverse effects are possible with many pigments. The plastic-based pigments are very intensely colored, but many people have reported reactions to them. There are also pigments that glow in the dark or in response to black (ultraviolet) light. These pigments are notoriously risky - some may be safe, but others are radioactive or otherwise toxic.

 

India ink

India ink is a generic term for a lamp black or carbon black ink, made from a finely ground carbon pigment in an aqueous solution with a binder. It can be thinned with water, yet it dries to a permanent, insoluble film. India inks first reached wide use in Europe in the seventeenth century, although crude recipes for them were already known in the sixteenth. Sticks of black ink that could be liquefied in water began to be imported from the East in the seventeenth century and were known as "Chinese ink" or "Indian ink" Local production followed.

It was found that this ink could produce beautiful grey washes as well.  In the nineteenth and twentieth centuries India ink with its strong black tone when used in concentration became an ideal medium for the hard, precise lines of the metal pen.

 

 

Canaletto. San Marco: the Crossing and North Transept, with Musicians Singing. 1766. Pen and ink with washes.

Sumi Ink Stick

This black sumi stick is made from powdered carbon of burnt pine or lamp black and a binding agent. When its end is dipped in the water well of a suzuri and rubbed over the suzuri's level surface, carbon particles fall off and dissolve in the water to produce ink.

 

Watercolors

Artist watercolors contain a full pigment load, suspended in a binder, generally natural gum arabic. Conventional watercolors are sold in moist form, in a tube, and are thinned and mixed on a dish or palette. Use them on paper and other absorbent surfaces that have been primed to accept water-based paint. Clean up with soap and water.

Liquid watercolors contain dyes as well as pigments, suspended in an aqueous medium. They are especially brilliant and transparent. Because they are moist and fluid, they are suited to thin washes and airbrush application as well as conventional brushwork. Many of the more brilliant colors are fugitive, so liquid watercolors are used most often for illustrations that will be scanned for reproduction.

Student grade watercolors have working characteristics similar to professional watercolors, but with lower concentrations of pigment, less expensive formulas, and a smaller range of colors. More expensive pigments are generally replicated by hues. Colors are designed to be mixed, although color strength is lower. Hues may not have the same mixing characteristics as regular full-strength colors.

Pan watercolors, available in professional as well as student and scholastic grades, offer pigment and binder in a dry form. Apply water with a brush to moisten the pan and lift pigment. Use a palette with indentations to mix colors. Pan watercolors are ideal for field and outdoor painting.

Scholastic watercolor pans contain inexpensive pigments and dyes suspended in a synthetic binder. Colors are chosen to be non-staining, easily washable, suitable for use even by young children with proper supervision. They are an excellent choice for teaching beginning artists the properties of color and the techniques of painting.

Gouache

Gouache is an opaque watercolor paint. Whereas transparent watercolors allow you to see the "white" of the paper below the paint, gouache can be applied in solid colors. This allows an artist to paint in layers from dark to light.

Gouache dries to a matte finish, which makes it easy to scan or reproduce electronically, since there is no glossy shine.

 

Acrylics

Artist acrylics are designed for painting on canvas, boards, paper, panels, and other prepared surfaces. Highly pigmented, they are generally of consistency similar to oil paint, preserving brush strokes. They can be used with a variety of painting techniques, including impasto and knife painting.

Iridescent, pearlescent, interference, and metallic acrylics combine conventional pigments with powdered mica (aluminum silicate) or powdered bronze to achieve complex effects. Colors have shimmering or reflective characteristics, depending on the coarseness or fineness of the powder. Iridescent colors are used in both fine arts and crafts.

Oil Paints

Artist oil paints contain a full pigment load, suspended in a binder, generally linseed oil or another drying oil such as safflower oil, poppy seed oil, or walnut oil. Use them on stretched canvas or boards that have been primed to accept oil paints. Clean-up with turpentine or mineral spirits.

 

 

Caution from Winsor & Newton

All colors are AP non-toxic, with the exception of the following colors, which bear the ACMI Caution Label:

Cobalt Violet, Cremnitz White, Flake White, Foundation White, Green Gold, Indian Yellow Deep, Juane Brilliant, Naples Yellow.