Sep. 02, 2024
Chemicals
White is the lightest color and is achromatic&#;that is, having no hue. White reflects all the colors of the visible light spectrum to the eyes. But technically, white is not a color like black; it is a shade&#;black and white augment colors.
The ideal white should be neutral in tint, neither cold nor warm, and opaque. The best white reflects the light most brilliantly. Besides its use as color, white is how light is introduced into painting. In mixtures with colors, it should change the value or tone of the blend without changing its hue. However, white cools all colors except blue, which is specifically cool. While there is no ideal white in paint, there are choices that artists can make to achieve a wide range of results in oil painting.
There are many more choices of white oil paint today than ever in art history. For thousands of years, lead white was the only choice for artists. By the nineteenth century, zinc white (zinc oxide) and lead sulfate were offered as alternatives to painters. By the twentieth century, titanium white (titanium dioxide) and lithopone (zinc sulfide/barium sulfate) were added to the roster of whites. During this time, artists&#; materials companies introduced mixed whites to artists, mixtures of two or more white pigments, often with extender pigments or fillers. Mixed whites were usually named Foundation white, Venetian white, etc.
White is not simply white. Each white oil paint has a hue bias, often called &#;temperature&#; by artists. Each white oil paint also has other properties, such as hiding power or opacity and tinting strength and how it flows or behaves under the brush or palette knife, known as rheology.
Color bias can be measured with a spectrophotometer to show the reflectance along each wavelength of visible light. In this example, the white paint is biased in the blue wavelengths, making it a cool white.
Every pigment has a color bias or temperature, meaning the color infringes on a neighboring hue on the color wheel. Even the purest primary colors of red, yellow, and blue have a color bias. They can never possess the purity of visible light. This color bias affects how the pigment mixes with others.
All white pigments have a bias so that when added to colors, they affect the hue of the final tint. If the white pigment has a bias toward the blue area of scattered light (cool), this can result in neutral tints with warm colors, sometimes referred to as &#;chalky&#; or &#;pastel.&#;
Understanding the color bias of white paint is essential to control the resulting mixtures of its tints better.
The tinting strength of white can be measured in tints with ultramarine blue.
Tinting strength is the ability of a pigment to alter the color of paint. Tinting strength is a qualitative measure of a pigment&#;s ability to resist color change when adding white pigment. The higher the tinting strength, the less its color changes when adding white, or conversely, more white must be added to affect its color.
The tinting strength of white is measured visually by how much it alters the color of a standard colored pigment, for example, ultramarine blue. The more opaque the white, the higher its tinting strength, and the more it will &#;reduce&#; the color. The higher the tinting strength, the lighter the value of the tint.
The hiding power of white can be measured in thin coats on a black background of the Leneta Chart.
The opacity of the coating determines the ability of the paint to mask the underlying substrate completely. Given the same paint film thickness, not all paint has the same opacity.
Opacity is a phenomenon that results from the complex interplay of various components, pigments, extenders, mediums, etc., and parameters, such as pigment dispersion, film thickness, etc., in a paint formulation.
Hiding power is related to opacity. Opacity is a film property, whereas hiding power is a property of the paint. There are several ways to measure the hiding power of paint; the most common is the contrast-ratio method. The contrast ratio is the reflectance of paint applied over a black surface divided by its reflectance when backed by a white surface. The ratio between these two reflectances is the contrast ratio. Opacity is the contrast ratio multiplied by 100 to get a percentage, where 100% is complete hiding.
The test method involves spreading the paint over a Leneta Chart (a paper card with black and white strips) and measuring the reflectance of the paint film in the white and black areas. The paint is spread over the card in a film of a specific thickness and left to dry.
Several factors influence the hiding strength (or opacity) of paint, such as:
The difference between the refractive indices of the pigment and the medium,
The particle size and shape, and degree of aggregation of the particles,
The proportion of pigment in the vehicle (i.e., pigment volume concentration or PVC) and
The thickness and porosity of the applied film.
Rheology is how the paint flows under a brush or when stirred with a knife.
How paint flows while being brushed or spread with a knife is essential to painters. The study of the flow or deformation of materials when subjected to stress is called rheology.
Rheology describes how the paint flows under different conditions, such as grinding on a mill or applying with a brush. There are three primary types of rheological behavior: shear-thinning, shear-thickening (dilatancy), and time-dependent shear-thinning (thixotropy). Such factors as pigment particle size and shape, particle surface energy, and binder properties influence the rheology of oil paint.
Lead white is basic lead carbonate, the double compound of lead carbonate and lead hydroxide. Artists have used lead white for thousands of years, known under the names of white lead, flake white and body white, Cremnitz or Kremnitz white, Crems or Krems white, Kremser white, London and Nottingham white, blanc d&#;argent or silver white, loot wit, ceruse, Dutch white, French white, Venetian white, Hamburgh white.
Dr. Jaap Boon, University of Amsterdam and AMOLF and formerly head of the MolArt Project offered these critical insights into the role of lead white in oil paint:
The role of lead white is multiple. It is a bulk drier, which means homogenous drying throughout the paint film. It reacts with free acids that develop by oxidation of the oil. It links the acids groups of C9 diacids even when they are still acyl glycerides, thus stabilizing the early film (proven by the NMR work of Michiel Verhoeven in ). At a later stage, when the ester bonds are gone, it further stabilizes the diacids to form a network that is difficult to break. Furthermore, it provides surfaces for oil-derived compounds to dock.
Without lead white, something else has to assume these roles. I don&#;t think that material has been found yet simply because we have only recently begun to understand the molecular structure of paints. I believe that &#; will bring us many defects in the oil paints that are now maturing. It is time to develop a molecular-level understanding of how to deal with oil paint defects that develop when the network can&#;t be stabilized with suitable metal cations.
This lead white in linseed oil is a smooth semi-opaque white that brushes long in the brushstroke direction. Its consistency is creamy and slightly ropey, yet it retains its shape as you manipulate it while being soft yet sculptural.
Colour Index: Pigment White 1 ()
Bias: Warm
Opacity: Semi-opaque
Drying Rate: 1
Lead white in walnut oil is brighter than ground in linseed oil due to the oil&#;s lighter color. It also behaves differently than lead white in linseed oil. It is long and &#;stringy,&#; forming thin strings of paint when brushed or spread with a knife. This lead white dries slower than linseed oil.
Colour Index: Pigment White 1 ()
Bias: Neutral
Opacity: Semi-opaque
Drying Rate: 2
Lead sulfate whites are pigments of lead(II) sulfate (PbSO4) or tribasic lead(II) sulfate (Pb4SO7). The pigment is a bright white with a white microcrystalline form. Lead sulfate is prepared by treating lead oxide, hydroxide, or carbonate with warm sulfuric acid or a soluble lead salt with sulfuric acid. It is also known as fast white, milk white, plumbous sulfate, or anglesite. According to George Field&#;s Chromatography, this color was known as Flemish white or sulfate of lead in the nineteenth century.
Flemish White is a warm white, slightly warmer than lead white. This warm white is semi-transparent, approximately that of lead white (somewhat less opaque than pure lead white), so it won&#;t kill colors in mixtures. It has a creamy, long, and stringy consistency that makes it excellent in pure highlights.
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Colour Index: Pigment White 2 ()
Bias: Warm
Opacity: Semi-transparent
Drying Rate: 3
Titanium white, also known as titanium dioxide, is an inorganic white pigment with Colour Index Pigment White 6 (PW6), or CI . Although mineral forms can appear black, they are white, water-insoluble solids. First mass-produced in , titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index.
Titanium white is mainly produced from the mineral ilmenite. The two naturally occurring forms of titanium dioxide, rutile, and anatase, are found widely in beach sands. Titanium white is made by two processes: sulfate and chloride. Both sulfate and chloride processes produce the titanium dioxide pigment in the rutile crystal form, but the sulfate process can be adjusted to make the anatase form. The rutile form of titanium white is the most common in artists&#; paints.
Surface treatment of titanium dioxide is essential for its durability in paint. Titanium dioxide adsorbs water onto the surfaces of its particles, forming hydroxyl ions in the process. The presence of hydroxyl groups makes the pigment sensitive to photochemical reactions and subsequent degradation. Treatment consists of coating the pigment particles of essentially colorless inorganic compounds by precipitating them onto the surface of the particles. Zirconium, tin, aluminum, and silicon compounds coat titanium dioxide, sometimes followed by an organic coating. The final surface can be hydrophobic or hydrophilic by selecting a particular organic compound. The coating prevents direct contact with the environment with the reactive surface of titanium dioxide, consequently improving the lightfastness and weather resistance of the pigment.
Today, most artists&#; paint utilizes rutile titanium white pigment that is surface-treated with an inorganic and organic coating. The anatase form of titanium white is rarely used in paint today.
Titanium white is ground in linseed oil without extender pigments or fillers. It is very opaque and is a cool white. The consistency is soft and buttery. It is ideal for making bright highlights and in mixtures with cool colors. Its slow drying can be offset by mixing it with lead white.
Colour Index: Pigment White 6 ()
Bias: Cool
Opacity: Opaque
Drying Rate: 4
Lithopone is produced by the co-precipitation and subsequent calcination of a mixture of zinc sulfide and barium sulfate. The ratio between the two components varies; for example, one type consists of a ratio of 60% zinc sulfide and 40% barium sulfate.
Lithopone is a bright white that is soft and stringy. Its smooth consistency makes it easy to blend colors, and slow drying provides greater open times for working with colors. It is an excellent alternative to zinc white.
Colour Index: Pigment White 5 ()
Bias: Cool
Opacity: Semi-opaque
Drying Rate: 4
Since introducing collapsible metal tubes, artists&#; materials manufacturers introduced colors based on mixtures of two or more pigments. White color mixtures are sold under various names according to the manufacturer&#;s preferences, such as Fondation white and flake white.
Lead-titanium white is a mixture of lead white and titanium white, providing nearly the same opacity as titanium white, a neutral white, and the density of lead white.
Colour Index: Pigment White 1 ()
Colour Index: Pigment White 6 ()
Bias: Neutral
Opacity: Semi-opaque
Drying Rate: 3
Crystal White is a semi-transparent white composed of lead white and leaded crystal glass in walnut oil. Finely powdered glass gives this white a novel refractive appearance in mixtures with other colors. Finely ground crystal glass (1.51) has a refractive index similar to oil (1.48), making it transparent and well-suited for mixing with other colors.
Colour Index: Pigment White 1 ()
Bias: Warm
Opacity: Semi-transparent
Drying Rate: 2
Mica Lead White is a semi-transparent lead white with a small amount of wet ground mica in walnut oil that provides a stiff white. Wet ground mica provides a crisp body with a lower refractive index than lead white, making it less opaque and well-suited for mixing with other colors.
Colour Index: Pigment White 1 ()
Colour Index: Pigment White 20 ()
Bias: Warm
Opacity: Semi-transparent
Drying Rate: 2
Venetian White is a semi-transparent white ground in a blend of pale linseed and walnut oil that provides a stiff white excellent for mixing with colors.
According to Salter&#;s edition of George Field&#;s Chromatography (), Venetian white was a commercial name in the nineteenth century for a white pigment mixture composed of equal parts of lead white (basic lead carbonate) and &#;heavy spar&#; (that is, the barium sulfate mineral barite or baryte). The names Venice white and Venice ceruse were also used for this mixture and for pure lead white. The white mineral barite has a lower refractive index than lead white, making it less opaque and better suited for mixing with other colors.
Colour Index: Pigment White 1 ()
Colour Index: Pigment White 22 ()
Bias: Warm
Opacity: Semi-transparent
Drying Rate: 2
Ceruse is made with lead white and a medium grade of dry-ground calcite (the calcium carbonate mineral) with a low oil absorption rate, like lead white, to maintain its quick-drying character. Calcite is semi-transparent in oil, giving ceruse its soft white texture. In the sixteenth century, this mixture of lead white and calcite was favored as a mixing white by artists such as Rembrandt and was known as lootwit in Dutch. The name ceruse originated from the Latin cerussa, referring to lead white pigment. In the nineteenth century, the name ceruse was used for white pigments that contained lead white and chalk and were associated with French lead whites mixed with differing amounts of chalk.
Colour Index: Pigment White 1 ()
Colour Index: Pigment White 18 ()
Bias: Warm
Opacity: Semi-transparent
Drying Rate: 2
Mixing White is a mixture of titanium white and barium sulfate (barite or baryte) with less opacity and slightly less brightness than titanium white. This mixed white is what titanium white consists of from most artists&#; oil paint brands, as they often do not disclose the presence of extender pigments. Adding barite or chalk reduces the powerful tinting strength of titanium white and provides a better body oil color.
Colour Index: Pigment White 6 ()
Colour Index: Pigment White 22 ()
Bias: Neutral
Opacity: Semi-opaque
Drying Rate: 3
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