Coatings Technology Handbook Episode 3 Part 8 doc

The composition of the vehicle used to make watercolor is basically unchanged from ancient times.. Artist’s Paints: Their Composition and History 117-5changes in vehicle technology came

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117-2 Coatings Technology Handbook, Third Edition

the paint that forms a film A synonym for vehicle is binder Vehicles come in many types The types that will be discussed in this chapter include oil, tempera (based on egg yolks), watercolor (based on gums, sugar, and starch), alkyd (normally a polyester), and latex (plural is latices, chemically these are emulsions) Artist’s colors are generally sold in two grades: professional and student The professional grade is generally used by those who make a living by producing and selling their artwork The student grade is intended for use by students who aspire to a career in art

There are many differences between the two grades The professional grade generally contains high percentages of pure color (pigment) Student grade is normally characterized by lower percentages of color Very often, student grade does not contain the “pure color” that is listed on the label In this case, the word “HUE” appears on the label This means that a single pigment or combination of pigments is being employed to approximate the “pure color.” Very often, the “pure color” is very expensive, while the hue is cheaper In addition, the hue rarely has the brilliance of the “pure color.” A further difference is that the student grade often contains extender pigments to help reduce cost while still maintaining the consistency (artist term for this is “feel”) of the professional grade

Artist’s colors are produced in a number of vehicle systems As vehicle systems evolved, so did pigments This chapter will outline historical development of vehicles and enumerate their compositions Con-jointly, this time-line formulary will contain the pigments associated with the system at discovery time

It will also list those pigments in use today, as well as what they replaced Discovery dates of pigments,

as well as the approximate date of first usage in artist’s colors, will also be listed

The very first artist’s color created by prehistoric man was a black made from charcoal This was used for drawing There was no binder involved — just pure charcoal put onto surfaces such as rocks, cave walls, and hides Soon after charcoal came into use, early man began using mud, which was available in various colors These muds were various shades of natural iron oxide pigments (yellow, red, and brown) and were applied directly to cave walls As was the case with charcoal, no binder was involved, just pure color These muds were derived from riverbanks, lakefronts, and other similar places They were used to create the now celebrated Cro-Magnon cave paintings The paintings were of stick figures They were thin lines of mud smeared across a cave wall in the form of a recognizable animal or human shape Art stayed at this stage until the ancient Egyptians invented watercolor

Watercolor came into prominence around 4700 B.C in ancient Egypt For the most part, watercolor

is based on a transparent pigment system The background of a brilliant white comes from the paper, which is used as the substrate It is utilized to make white and light tints Pigmentation consists of both transparent and nontransparent colors The nontransparent colors are applied in an extremely diluted state These colors are diluted to the point where they are almost as brilliant as the transparent colors There is an alternate pigment system that employs white pigment as an opacifier The choice of pigment system, whether in ancient times or today, has always been left to the artist Neither system is wrong nor better The choice depends on the desired artistic effect

The palette (pigment choice) available in ancient Egypt for use in watercolor included a host of list is set up by color type This is then broken down to individual colors designated by color title and composition

The composition of the vehicle used to make watercolor is basically unchanged from ancient times The major ingredients used by the Egyptians were gum arabic (a product of Somalia), water, sugar syrup, glycerin, dried extract of ox bile, and dextrin, which is derived from white potatoes Some more modern formulae replace the sugar syrup with pure glucose The ox bile can be replaced with modern wetting agents of the type generally associated with latex house paint production The ancient Egyptians had no need to use a preservative, because arid conditions in Egypt produced an atmosphere in which bacteria could not survive

There is a system of similar composition called Gouache (pronounced GWASH) This system uses the same vehicle but employs opaque colors, usually with extender pigment added to increase dry opacity Both systems employ the same pigmentation types

DK4036_book.fm Page 2 Monday, April 25, 2005 12:18 PM

pigments known from the dawn of recorded history Table 117.1 lists colors used by the Egyptians The

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Now let us turn our attention to oil color Oil color, which was invented in the year 1400 A.D., originally had a palette that was very similar to that of the ancient watercolor palette The most noticeable exception

is the addition of a white color called Flake White (basic lead carbonate) Technology to make basic lead carbonate dates back to the days of ancient Rome Another color, which, if it did not exist in the year

1400, was available shortly thereafter, is Naples Yellow In its original form, Naples Yellow was lead antimoniate Today, it is made as a hue from a combination of Cadmium Yellow, zinc oxide and Ochre (Natural Yellow iron oxide)

As time went on, the modern palette evolved to the point where it matched the modern watercolor palette with the exceptions noted above The composition of oil color is fairly simple Generally, only three items are used in an oil color formula They are the colored pigment, the oil (usually alkali refined linseed oil) and a stabilizer (normally aluminum stearate) Over the years, different grades of oil have been used to make oil color In the beginning of the 15th century, only raw linseed oil was available Soon afterward, purification by heating was discovered At the same time, people learned how to make

“sun-bleached linseed oil.” This is made by mixing linseed oil with water and exposing the mix to sunlight The water acts to remove impurities in the oil, while the sun bleaches and lightens the oil After a few weeks or months of exposure, the oil is separated from the water and then used In later years, oil made

by this technique was called “superior linseed oil.” By the 17th century, both stand oil and refined linseed oil were in common use Stand oil is partially polymerized linseed oil The oil is polymerized by heating

it to 550 ± 25˚F and maintaining that temperature for a few hours This causes the viscosity to increase significantly A number of other effects can also be seen These include the excellent leveling and gloss Upon aging in dry films, stand oil shows much less yellowing than regular linseed oil Less polymerization occurs during drying, because it is partially polymerized during the heating process This, in turn, leads

to less yellowing

Originally, refined linseed oil was refined by an acid process The mechanism called for acid (usually sulfuric acid) and water to be added to the oil This removes impurities and lightens color The best grades have all the water and acid removed before packaging While acid refined linseed oil is still available,

it has, for the most part, been replaced by alkali refined linseed oil Here, a strong alkali replaces the acid The use of alkali to refine linseed oil often removes more impurities and provides better color than would

be seen with the use of acid as the refining agent

Occasionally, other types of oil are used in the formulation of artist’s colors The most notable of these

is poppyseed oil It is used mainly in whites, because it is naturally colorless This makes a white paint made from it appear “whiter” than paint made from amber-colored linseed oil Less frequently, walnut oil is used as a linseed oil replacement Walnut oil has the same clarity as poppyseed oil, but, upon aging,

it can turn rancid and give off a strong odor While the paint is perfectly useable, the perception of quality

is totally ruined

Well-formulated oil-based paint dries to a glossy, durable finish The pigment volume concentration (PVC) is low, especially when compared to other types of artist’s colors A good example of this is tempera paints Tempera and oil color were invented at the same time, but, due to tempera’s radically different composition, it dries to a flat finish The finish is due to the high PVC of the paint The high PVC is a result of the tempera vehicle Tempera paint was the first emulsion paint ever created This emulsion is

a naturally occurring phenomenon The basis of tempera is egg yolk The yolk contains a water solution

of albumin, a nondrying oil called egg oil, and lecithin Each ingredient has its own function The albumin

is a binder When heated, albumin will coagulate to form a tough, insoluble permanent film A cooked egg is an example of this coagulation Likewise, when albumin is diluted with water and spread out in a thin film to be dried by sunlight, it coagulates to form a film The egg oil acts as a plasticizer, and the lecithin is an excellent emulsifier All that is needed to create a tempera paint from the yolk is pigment and water Over the years, egg yolks were replaced with other substances to form alternate tempera paints These emulsions are based on any of the following: gum arabic, wax, casein, and oil All have some degree

of acceptance

After the acceptance of oil and tempera colors in the 15th century, creativity to develop new vehicles fell into a dark age Yes, pigments did continue to develop However, vehicles did not The next few DK4036_book.fm Page 4 Monday, April 25, 2005 12:18 PM

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Artist’s Paints: Their Composition and History 117-5

changes in vehicle technology came in the 1920s Two developments occurred simultaneously These were the invention of the alkyd resin and the development of latex emulsions The original alkyds were made

by the reaction of glycerol (a polyhydric alcohol) with phthalic anhydride (a polybasic acid) in an oil medium In time, glycerol was replaced by pentaerythritol (penta imparts greater flexibility and color stability to the resin) Alkyds were originally used in industrial and house paint systems However, around

1960, some manufacturers of artist’s paints began to partially replace linseed oil in selected colors Full product lines based upon alkyd resin technology did not appear until the late 1970s/early 1980s Today, almost every artist’s paint producer has a full line of alkyd colors

In the late 1920s, latex emulsion technology was also emerging The original latices were made from styrene-butadiene These were very poor in quality Sometimes the emulsion would break Sometimes reactions after processing occurred These reactions included gelation and seeding of the emulsion In the 1930s, resin producers began using methylmethacrylate as a basis for emulsions By the end of World War II, latex emulsions were being used in house paint formulae By 1952, boutique art shops began carrying a line of latex (now called acrylic) colors The name change was the result of the switch from styrene-butadiene to methylmethacrylate By 1960, all major manufacturers had complete lines of acrylic colors The color palette for acrylic colors is the same as the palette for watercolor There is no Flake White (basic lead carbonate) or zinc oxide due to the reactivity of these pigments with the latex The last advance in artist’s paint technology came in 1993, with the advent of water-thinnable linseed oil paint As stated earlier, water-thinnable linseed oil paint was created by dismissing the old myth that water and oil did not mix Chemists were able to do this alteration of linseed oil Linseed oil is a composite

of between 17 to 21 different fatty acids The number varies with the source of the oil, as is the case with most naturally occurring materials All of these fatty acids are at varying percentage levels in the oil Some of these acids are hydrophobic, while some are hydrophilic By adding more of the hydrophilic acids, an oil that will accept water by forming a temporary emulsion is made The beauty of water-thinnable oil colors is that they eliminate the need for solvents by serving as both thinner and cleanup agent This greatly reduces studio toxicity If, however, one wishes to use the solvents that have been used since the 15th century, the system will accept them The palette that is in use for water-thinnable oil colors is the same as the palette for conventional oil color

composition of the pigment, the date of discovery, the date of first usage in artist’s colors, and the pigment replaced This table refers only to pigment Vehicle type has been deleted All colors listed are available

in all vehicle types described herein, with very few exceptions In the discovery and first usage columns, the notation “Ant” means that the discovery or first usage goes back into antiquity

Hopefully, this gives the reader an overview of the history and composition of artist’s paints DK4036_book.fm Page 5 Monday, April 25, 2005 12:18 PM

Table 117.2 summarizes the modern palette Listed are the artist’s name for a color, the chemical

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Artist’s Paints: Their Composition and History 117-7

Naples Yellow Hue Mixture of zinc oxide,

Cadmium Yellow, and Yellow Oxide

Not Applic 1920s Lead antimoniate (known

since the 1500s) Phthalocyanine Blue A 16-member ring comprised

of four isoindole groups connected by four nitrogen atoms; in the center of the ring is a copper atom

1935 1936 Prussian Blue

(ferric-ferrocyanide) discovered

in 1704 and introduced in 1724

Phthalocyanine Green Same as Phthalocyanine Blue

but four chlorine atoms are added to each isoindole group

Quinacridone Colors

1 Red (Yellow shade) Gamma trans-linear

Quinacridone

2 Red (Blue shade) Gamma trans-linear

Quinacridone

3 Violet Beta trans-linear

quinacridone

4 Magenta Disulfonated trans-linear

Quinacridone

Raw Sienna A natural earth composed

mainly of hydrous silicates and oxides of iron and aluminum

Raw Umber A natural earth composed

mainly of hydrous silicates and oxides of iron and manganese

Titanium White Mainly titanium dioxide

~60% with some zinc oxide and/or barium sulfate ~40%

combined

1870 1920 Flake White (basic lead

carbonate) known since antiquity

Ultramarine Colors

1 Blue

2 Green

3 Red

4 Violet

All are complex silicates of sodium and aluminum with sulfer The degree of sulfonization determines the color

Lapis lazuli

Vermillion Mercuric sulfide Ant 8th century Cinnibar, an ore with

mercuric sulfide in it

Yellow Ochre A mixture of synthetic

hydrous iron oxide with alumina and silica

19th century 19th century Natural version of the same

mixture It dates into antiquity

watercolor;

1900 in oil color

Chalk (calcium carbonate) Flake White (basic lead carbonate)

Source: Lewis, Peter A., Federation Series on Coatings Technology-Organic Pigments, 3rd ed., revised September 2000 Mayer, Ralph, The Artist’s Handbook of Materials and Techniques, 3rd ed., revised 1970.

TABLE 117.2 The Modern Palette (Continued)

Artist’s Name Chemical Composition Discovery Date

First Used Date Pigment Replaced DK4036_book.fm Page 7 Monday, April 25, 2005 12:18 PM

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118 Fade Resistance of Lithographic Inks —

A New Path Forward: Real World Exposures in

Florida and Arizona

Compared to Accelerated Xenon Arc

Exposures

118.1 Florida and Arizona Outdoor under Glass Exposures 118-2

118.2 Accelerated Xenon Arc Exposures 118-5

118.3

How long will an ink remain fade resistant under the variety of lighting conditions that it may encounter during its service life? What is the cost of product failure? What is the price/performance trade-off between affordability and performance? Is there a quick method to determine which ink is best for a specific application? This paper answers these questions and provides a useful roadmap for assessing ink durability First, results are presented from real world sunlight through window glass exposures in Florida and Arizona These internationally recognized test locations provide a “worst case” scenario by exposing inks

to high ultraviolet (UV), high temperatures, and high relative humidity (RH)

Second, test results are presented from laboratory xenon arc exposures performed on an identical set

of lithographic ink specimens The purpose was twofold: (1) How well do laboratory xenon exposures correlate with Florida and Arizona exposures in terms of actual degradation and relative rank order? (2) How much faster are the accelerated laboratory exposures compared to the natural exposures?

This definitive study correlates real world and accelerated laboratory test results for lithographic inks

Eric T Everett

Q-Panel Lab Products

John Lind

Graphic Arts Technical Foundation (GATF)

John Stack

National Institute for Occupational Safety & Health/National Personal Protective Technology Laboratory

Test Program • Effect of Seasonal Variation • Arizona Exposure

Conclusions 118-9

Compared to Florida Outdoor under Glass Exposure

Further Reading 118-10

Test Results • Relative Humidity • Xenon Arc Exposure

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Fade Resistance of Lithographic Inks 118-3

FIGURE 118.2 GATF technical staff selected eight representative lithographic ink colors printed on a standard substrate for fade resistance testing.

FIGURE 118.3 Ink specimens were placed in ASTM G24 glass-covered exposure racks in Florida and Arizona benchmark locations.

TABLE 118.1 Total Sunlight Outdoor Exposure Summary MJ/m 2 at 300 to 3000 nm

Florida winter 90 1541.13 Florida spring 90 1252.54 Florida summer 90 1081.73

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However, by 35 d, the inks exhibited a wide range of fade resistance, from excellent to poor Therefore,

35 d was chosen to evaluate the performance of the inks in the various outdoor exposures

Figure 118.5 shows the range of durability for the three Yellow ink test specimens in the Florida fall exposure Despite being the same color, the three Yellow inks had significant differences in their fade resistance Yellow A performed dramatically better than Yellow B or Yellow C This is because Yellow A

is fade resistant and suitable for fine art reproductions or outdoor applications, while Yellow B and C are intended for general commercial printing

FIGURE 118.4 Fade resistance range for eight colors.

FIGURE 118.5 Fade resistance range for one color.

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FIGURE 118.7 Fade resistance correlation for Florida: winter vs summer.

FIGURE 118.8 Fade resistance correlation: Florida: vs Arizona.

TABLE 118.2 Rank Order Correlation Matrix

Florida Summer Florida Fall Florida Winter Florida Spring Arizona Fall

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FIGURE 118.10 GATF and Q-Lab tested inks in Q-Sun Xenon Test Chambers.

TABLE 118.3 Xenon Arc Exposure Test Conditions Q-Sun Xenon (Xe-1 and Xe-3H)

ASTM D3424, Method 3 Window Glass Filter Irradiance Level: 0.55 W/m 2 /nm at 340 nm RH: Xe-1 Effective RH = 15%

Xe-3 RH = 50%

Exposure Cycle: Continuous Light at 63 ± 3 ° C (145 ± 5 ° F) Test Duration: 31 d

Total Radiant Exposure = 1473 kJ/m 2 at 340 nm

FIGURE 118.11 Q-Sun fade resistance range.

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