Casein

Casein is a milk protein which was commonly used by painters in the past as a binder to make a paint with characteristics similar to egg tempera. At one time, casein was a common glue used in cabinetmaking and was know for its great strength. A powdered form of casein is made by drying the curd of soured skim milk (the milk fats from whole milk are nondrying oils and must be removed). Today, casein is prepared commercially by heating and acidifying skim milk and then drying it to produce a powder, which is only soluble in  water  if  made alkaline. One way to prepare a casein solution  is  to  soak  the powder  in  water and then add calcium hydroxide, which can be purchased  from a chemical  sup­  ply company. Fortunately, most casein powder, when it  can  be  found,  is in  a form that will mix readily with water.

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The use of casein is said to date back to the Egyptians. It was also used as an alternative to rabbit-skin glue for sizing canvas because it could be applied cold. The first commercially produced casein was marketed in the nineteenth century. The Pelikan Company of Germany produces casein paint called Plaka, which can be found in most artists' material stores. Its consistency allows for application by either brush or palette knife. It adheres well to paper,  paperboards,  wood, plas­ter, plastic, glass, and metal. It dries matte with a velvetlike finish and becomes waterproof in twenty-four hours. Outdoor use requires a final, protective varnish. Casein paint has some drawbacks;  although  it  is  highly  water-resistant, it is not truly waterproof, and it is brittle and becomes  more so as it ages. Therefore, the thicker the paint film, the more rigid the support should be. In general, thick applications of casein paint should be avoided. Adding a little drying oil, such as linseed oil, to casein paint will reduce potential  cracking,  but  will slow  the drying time and add some yellowing properties. Casein paints dry very quickly and look like oil paint except that they have a matte finish. The popularity of casein waned with the introduction of polymer  emulsion paints, which have almost all the advantages of casein paint with none of the drawbacks.

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Ink

AN INK is a watercolor that is already diluted for convenience  and whose color­  ant tends to remain in solution. An ink is composed of a pigment or dye that is suspended and stabilized in water. Glue, gum arabic, gelatin, shellac with borax, and soap are some of the more common ingredients used to  maintain  a suspen­sion and provide a binding agent.

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The most common form of ink, dating from about 250 B.C. to approximately 1100, was a carbon black ink with a glue or gum binder. At  this  time,  it  was found that the mixing  of  a  natural  iron  salt-ferrous  sulfate-with  an  extract from nutgalls, which are high in tannic acid, resulted in a chemical reaction that produced a blue-black ink. This method of ink production was considered an improvement; however, it was not lightfast and the particles that remained• in the ink from the chemical reaction did nothing  to  improve  flow  characteristics.  It was the development of synthetic dyes, during the nineteenth century, that paved the way for the fountain  pen. Inks could now  be made from true solutions,  with no particles to clog a writing instrument.

 

India Ink

The term "India ink," or "China ink," originally referred  to  a  lampblack  (car­ bon) ink in stick form produced in either China or  Japan.  Today,  "India  ink" refers to any ink made of carbon that is also waterproof. Some manufacturers of India ink still use carbon from Oriental ink sticks. Shellac is commonly  used  as the binder for this ink and makes it waterproof. India ink should not contain

n any dye.

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There are two methods of testing an  ink  to see if  it  is a dye  composite.  A drop of ink placed on   piece of absorbent  paper will spread out and feather at the edge. An ink that  is a dye composite  will  produce  a two-colored  edge,  such as  a  blue-black  and  maroon,  within  a  few  hours,   and a carbon   black   ink   will not. The second method is  to place some of  this ink on  paper  in direct  sunlight for one day. If there is any evidence of fading, it is not a carbon ink.

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Non-waterproof India inks

are available-they are made primarily for use in fountain pens. The absence of shellac reduces the possibility of clogging. Non­ waterproof India inks always state on the label either "non-waterproof" or "fount." Only such inks should be used in a fountain  pen.  However,  the  use of any India ink, waterproof or not, will void most fountain pen warranties.

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It would seem that the centuries of continuous  use  of  India ink in  both  writing and drawing can be attributed to the simplicity its use  and  its  great  perma­nence.

 

Drawing Inks

The term "drawing ink" refers to both India ink and colored  waterproof  inks. Until recently, colored drawing inks were known for being highly  fugitive.  Today, there are several transparent dye composites, and several semi-opaque pigmented inks that are labeled lightfast. These-and only these-may be  con­sidered for fine artwork, but remember that lightfastness of such products often meets only the minimum standards.

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Fountain Pen Ink

Conventional fountain pen inks are dyes dissolved in water, or water-alcohol mixtures, with a non-waterproof binder. This allows the ink  to flow  freely  with­ out clogging the pen. Until recently, almost all fountain pen inks were highly fugitive and could only be preserved by protection from exposure to light. The recent resurgence of interest in calligraphy, combined with the manufacture of calligraphy fountain pens, generated a demand for fountain pen inks, especially colored inks, that did not fade when the finished product was framed and dis­ played. Today, there are several companies producing a limited range of both waterproof and non-waterproof and pigmented and dye-composite inks that can be used in fountain pens. However, they are new and should  be used with caution, and only after reading any restrictions described on the label.

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Inks for Technical Pens

Permanence, opacity, and being waterproof are high priorities in a technical pen ink. Technical pens, which  are used  in drafting  and illustration,  are designed  to be used with permanent, opaque waterproof ink that  would ruin any other foun­tain pen. (Technical pens do require some maintenance or they, too, will be rendered useless by such inks.) Inks made for technical pens often  meet  mini­ mum lightfastness standards for fine artwork, and may be used for such, if  they are labeled "lightfast."

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As the use of  technical  pens has widened, so has the selection of inks for use   in them. Today, transparent and opaque and matte and gloss inks are available. There are also inks that work on plastic  surfaces,  such  as acetate  and drafting film. The flow, or working characteristics, of ink are often very different  from brand to brand. Some inks, like those produced  by  Koh-i-noor  Rapidiograph, seem to be made with density foremost  in  mind,  and  are  not as free  flowing. This quality is ideal for drafting, where exacting reproduction of drawings is required. For fine artwork, however, flow is often more important  than  density, and many other companies produce thinner  inks that  flow  more easily. It is wise to sample several brands  to see Whatever  ink  you select, it should never be used in a fountain pen.

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Oriental Inks and Watercolors

All the research on inks and watercolors leads back, again and again, to China and Japan. Calligraphy itself is the oldest form of abstract art, and watercolor painting developed from it. It would seem almost impossible to master waterborne media without some appreciation for the source of it all. And to appreciate the art of the East is to appreciate the nature of its materials, for they are inseparable. It would also help to understand that the selection of Oriental materials is more subjective than objective. It is possible, for example, to choose from as many as fifty different shades of black, ranging from warm blacks to cold blacks, all of the same level of quality. In such a case, how could a choice be anything but subjective-how can one shade be said to be better than another unless it meets your own particular needs or desires?

The best guidelines for the novice are price and previous exposure. With Oriental materials, price is a good indicator of quality because, in general, if it costs more, it's usually better. Another guideline is not to overbuy. If, for example, you have never before been exposed to ink sticks and ink stones, it is unlikely that you will be able to experience the subtle differences between their levels of quality and you would be wise to buy conservatively.

INK STICKS

In the Orient, ink is found in the traditional form of a solid stick. Liquid ink is made by rubbing the ink stick against the wet surface of a particular type of stone. Ink sticks are made by burning either vegetable oils (such as sesame oil, rapeseed oil, and paulownia oil), or pine wood and pine resin and collecting the soot, or lampblack, which is then combined with animal hide or bone glue, spices, and minerals. The mixture is compressed and dried into a stick.

Ink sticks made from vegetable oils tend to produce a warm black ink, with a hint of brown or purple. Calligraphy inks are made primarily from oils and their exact shade is often regulated by the addition of various plant matter, as well as the source of the glue (what type of animal and whether the shin or other bones were used). The plant matter and glue are added to the soot before the stick is molded. A shine is considered a desirable characteristic in a calligraphy ink and an undesirable characteristic in an ink for painting. The shine is regulated by the particle size of the soot as well as through the addition of plant matter.

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Inks made for painting do not contain any additional plant matter and the particle size is selected to give a matte appearance, so that the subtlety of the painting can be seen without distraction. Painting inks are made from either vegetable oils or pine. Those made from pine soot produce a cool, bluish-black ink, which has a lighter appearance than those made from oil. Pine-soot inks are used for washes as well as for the overall background of a painting. The darker inks made from oil are used for the final details and for contrast.

When starting or testing a new ink stick, never use the first grind because ink sticks often have a coating that is best removed before use. One method of testing an ink is to dilute the freshly ground ink so that it can be used as a wash. Then make a brush stroke where, at some point, you reverse the direction, going over a part of the area previously painted. If the area or edge of the previously painted area maintains its integrity, it is a good sign. The more it dissolves, the less desirable the ink is. Some inks look better while they are still damp on the paper and become dead when dry, while others look better after drying than while in use; you should therefore wait until inks are dry to inspect them.
Oriental ink sticks are like wines; their quality is determined as much by the aging process as by method of preparation. An ink stick should be aged for at least one year (two to three years is preferable) before use, and, indeed, some of the very best sticks are more than four hundred years old. The aging process involves the natural oxidation of the protein that makes up the glue. According to Baku-undo U.S.A., Inc., only ink sticks that are handmade truly benefit from this aging process, and for this reason it distributes only handmade ink sticks that have been aged for a minimum of five years. Prices for Oriental ink sticks range from $1.50 to several thousand dollars for the highest-quality sticks that are several centuries old.

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Chinese Ink Sticks are made primarily from pine trees that are high in resin and therefore characteristically produce a bluish-black ink. However, there are always exceptions because the addition of minerals and spices may change the hue. The Chinese make ink sticks throughout the year without regard to changes in weather. This, unfortunately, can result in an ink stick cracking when it is later shipped to parts of the world that have dramatically different temperatures and humidity. Broken ink sticks can sometimes be repaired by wetting' the two broken ends and holding them together until they dry. Producing ink sticks year round also results in some inconsistencies in quality. The

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Chinese grade their ink sticks using a series of three-digit numbers.

101-The best professional quality commercially available
 

102-Very good, professional quality
 

103-Good, professional quality
 

104-Amateur
 

105 or higher-Student

Japanese Ink Sticks are usually made from vegetable oils and therefore tend to produce warmer blacks. But, because so much of Japanese history involves Chinese influence, blue-black ink sticks made from pine in Japan are commonly
available. Many Japanese ink sticks have camphor added, which gives a silvery black appearance to the ink when it is used full strength. The illusion of silver flecks can be seen when the image is held to the light at an angle.

The Japanese make ink at only one time during the year (in the autumn), to reduce the possibility of cracking and to improve consistency. Buying Chinese ink is always a gamble even when purchasing a second stick made by the same family in China. It could be among the world's best or the world's worst. The Japanese go for consistency, so you may not get the world's best, but you also will not get the world's worst. They have good, constant quality so the second purchase will be like the first.

The Japanese utilize a series of dots to classify the quality of their inks. Five dots on the end of the stock indicate the finest quality, while fewer dots signify a lesser quality. Unfortunately, certain Japanese manufacturers sometimes take advantage of the beginner's limited knowledge in this area by putting five dots on their lowest-quality sticks and, in some cases, adding blue dye to ink sticks made from vegetable oils. Price should be some indication of quality.
 

BOTTLED ORIENTAL INK

In China and Japan, the use of bottled ink is frowned upon and generally considered to be a concession to barbarians. There are, however, several brands of Oriental ink from China and Japan that come ready for use in bottles. The best is not as good as the ink that comes in stick form, but it is usually superior to Western bottled ink.

Many manufacturers have switched from using animal glues to using acrylic polymers as a binder for the ink. These acrylic inks have a longer shelf life of seven to ten years, as opposed to the two to three years of inks that have animal glue binders. Acrylic inks also tend to be waterproof, rather than water-resistant. Consequently, it is more· difficult to shade an area properly after an acrylic has dried. An acrylic ink can also ruin a brush that is left to dry in it, while animal glue inks can almost always be redissolved. The better grades of bottled ink are still made with animal glue.
Ink paste, which is a concentrated form of liquid ink, is also manufactured in as large a variety as bottled ink. Few stores, however, carry an equal variety.

INK STONES

Natural ink stones are made from slate, and imitation ink stones are ceramic. The ink stone, with water, is used to grind the ink stick into tiny particles to form liquid ink. The better the stone, the smaller and more consistent the particles will be and the denser the ink. A good stone will make a poor ink stick perform slightly better than a good ink stick ground on a poor stone. It is best to have a stone that at least matches or slightly exceeds the quality of the ink stick.
The older the stone that is used to make an ink stone, the better it will perform. Because the geological formations in China are much older than those in Japan, the best stones come from China. Both the Japanese and Chinese make their best products out of the oldest stone that can be found in China. The Japanese term for the best grades of slate used in the manufacture of ink stone is tankai.

 

There are several grades of tankai just as there are grades of diamonds. The very best tankai was found under rivers. Today it can only be found in private collections and in museums. Since China has a long history, all the stones of this quality have already been found. Today's tankai is collected from caves and these lesser grades of tanka; can be found even in the West, but they are expensive. Japanese ink stones that are more moderately priced are made primarily from more recent lava formations. The least expensive ink stones are made from ceramic rather than from natural stone. (For colored ink sticks, multiple ceramic stones are used because of the expense and to keep the better stone from being contaminated with residual colors.)

Japanese ink stones are made into a rectangular shape with a well, or deeper impression, on one side to hold the water separate from the grinding surface and to collect the ink. The better natural stones are often characterized by a natural irregular shape, or are encased in a wooden box.

Chinese ink stones are usually round in shape with either a concave or a flat grinding surface. It is also common to find a lid, which covers the stone, made of wood or of the same stone. The moderately priced stones are made of slate. Better quality is sometimes indicated by the irregular shape, a wooden encasement, and the purplish hue of the stone. Some Chinese ink stones have an oil or wax on them to help protect them until purchase. This material should be washed away before use.

Inspecting an Ink Stone involves looking for any hairline cracks that may result in the stone coming apart easily, and checking to see if it is a ceramic stone or a natural stone. If there are any natural imperfections such as streaks that appear to run with the tooth, or grain, of the stone, they are not necessarily to be avoided and are, in fact, sometimes sought after for the character that they give.

Testing an Ink Stone involves three steps of inspecting the grinding surface. The finer the surface, the finer and more consistent the quality of the ink will be. The surface of an ink stone is similar to a saw's teeth, in that there are tiny peaks tilted in one direction that can grind off small particles of the ink stick when rubbed against it. The first step is to test the tooth of the stone's grinding surface. This can be done by rubbing the surface of the ink stone with the tor edge of a fingernail in a direction away from the well. The better the stone, the more distinct and uniform the mark will be.

The next test involves the use of water. If the tooth is fine and pointed in one direction, a small amount of water placed on the (clean) grinding surface will appear to sink immediately just below the surface, but will not appear dry. The teeth will break the water tension and the water will be trapped beneath the tips of the teeth. If the surface where the water has been applied dries out quickly, then the stone is too absorbent and of lesser quality. If the grain is irregular or has imperfections, the absorption will also be irregular.

The final test is to check the flatness and smoothness of the grinding surface. Visual inspection and touching the surface with the fingers or tongue should show a very smooth and flat surface. Ink stones range in price from three dollars to eighty thousand dollars, depending on quality. A stone of adequate quality can easily be had for between ten and thirty dollars.

A complete inspection should be reserved for the more expensive ink stones. Performing an inspection this thoroughly on an ink stone that is priced at less than ten dollars, is like using a jeweler's eyepiece to inspect jewelry at the comer drugstore.

ORIENTAL WATERCOLORS

The major difference between Western watercolors and Oriental watercolors is that in the Oriental system some colors are by tradition opaque, and others are transparent. They are sold in the form of a dry cake in a ceramic dish, or in a powdered form where the liquid binder is mixed in with water to make watercolor, or in colored ink sticks. (Although none of these materials should be considered nontoxic, traditional vermilion ink sticks, because they are made from mercuric sulfide, are highly poisonous and should be used with caution.)

 

The best Chinese watercolors come in a very limited number of colors and are in the form of little chips that are dissolved in water to make the color. With the exception of these chips, most of the Oriental colors available in this country are not of the first quality. Today, most instructors of Chinese and Tibetan painting who live in the West recommend the use of the finest tube Western watercolors and gouache over the lesser-quality Oriental watercolors.
 

"NEW EARTH COLORS"

These colors are artificial mineral pigments made of glass frits. They are similar to Egyptian blue in that their color depends on how finely ground the particles of pigment are. The main ingredient is lead borate glass, which is fused into such color-producing agents as metallic cobalt and chrome, and then ground. The ground glass particles are then separated according to size, which also determines the color. Holbein makes a line of these pigments, which have been used in Oriental watercolors and are currently being tested for possible application in Western artists' materials. By employing this method of manufacture, they are able to make as many as two hundred different shades from a few basic colors.

SEAL INK

Although seal ink is not a watercolor, it is used to sign a piece of calligraphy or an Oriental-style painting. A chop, which is like a rubber stamp made of wood or bone, has the artist's name or symbols carved on the face. The face of the chop is pressed gently into the surface of the seal ink (sometimes it is necessary to touch the seal ink several times to collect enough ink on the chop's surface). In some traditions, the seal is placed so that it just touches the edge of the still damp ink, or watercolor, because the slight mixing that occurs is impossible to forge, and the original can be proved.

The seal ink container usually has a loose-fitting cover to allow for a thin piece of silk to be placed over the ink surface. This piece of material serves to keep the surface moist so it can be reshaped through the silk.

The best seal ink is made from genuine vermilion from China, which is composed of mercuric sulfide and is extremely poisonous.

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Polymer Emulsion Paints and Media

AN EMULSION is the suspension of tiny solids in a liquid. Milk is an example of an emulsion, and most solids, if made small enough, will tend to remain in suspension. A polymer is a larger molecule made of smaller and simpler chemical units most often arranged in a chainlike formation. A polymer emulsion is the suspension of polymers in a liquid. As the liquid evaporates, the suspended polymer solids come closer together until they touch and combine to form larger chains and eventually a film. A paint can be made by pigmenting a polymer emulsion. The type of polymer used determines the type of paint or medium acrylic polymers for acrylic paints and vinyl polymers for vinyl paints.

Polymer emulsion paints, by comparison with oil paints and watercolors, have a short history, which began in late 1948 with the development of polyvinyl acetate emulsion (PVA) , commonly known as white glue. However, PYA was too sensitive to water and heat, and the paints made from it were not durable. The acrylic polymer emulsions now used in artists' paints are a byproduct of the attempt to develop a new type of house paint during the early 1950s. (Today, however, the amount of actual acrylic binder in house paint is often quite low. In some states it can be as low as 20 percent and still be called acrylic paint. This would be too low to use in fine artwork.) The first artists' acrylic polymer paint became readily available in North America around 1963 and in Europe about two years later.

THE MANUFACTURE OF POLYMER EMULSION PAINT

The manufacture of polymer emulsion paints is a balancing act. Mixing dry pigment directly into a polymer emulsion rarely creates a usable paint. Several additives are needed to produce a workable paint. The polymer solids must be coated with emulsifiers to prevent them from binding together before the liquid evaporates. Dispersants are necessary to keep the pigments that are added from clumping together and/or settling out of the liquid. Antifoaming agents are needed to prevent foaming during the application of a paint so that the dried paint film does not have a craterlike surface. Wet-edge agents, such as ethylene glycol (very poisonous) or propylene glycol (less effective, but nontoxic), are used to regulate the drying time, allowing sufficient time for mixing and applying the paint. Thickeners are used to transform the milky quality into a paint like consistency. And last but not least important, a preservative is added. The type of paint film that is formed depends on the specific polymer formulation used. For example, the Rohm and Haas Company, the supplier of acrylic emulsion to all paint manufacturers in North America and many parts of the world, offers several varieties of 100 percent acrylic emulsion (of which 44 and 47 percent of the emulsion is composed of resin solids). Rhoplex is the name it has given to its acrylic emulsion and each formulation is assigned its own number. The most commonly used emulsions that are dispersed in water are AC-22, AC-33, AC-34 , AC-35, and AC-235. (There are also acrylic solutions such as Acryloid F-lO, which is 40 percent resin solids in mineral thinner which are used in the manufacture of paint varnishes and acrylic paints that can be thinned with mineral spirits.) AC-22 has good flow and leveling properties, but is less durable than the other formula. AC-33 was the first formula used in the arts and is still commonly used. AC-34 was designed for outdoor use on wood, but tends to be slightly more brittle. AC-235, the improved version of AC-35 , is used to give paint a thicker quality and would be used in impasto painting.
Since each of these funnels has desirable qualities as well as undesirable qualities, most paint manufacturers blend the various polymers like chefs to obtain, what is in their opinions, the best working characteristics. A blend of more than one polymer is referred to as co-polymers; virtually all artist acrylic and vinyl paints are co-polymers.
The physical process of making acrylics resembles the process one would more expect to see in a pastry shop than in a paint mill. Some manufacturers do not use rollers to grind the paint mixture as would be done with oil paints, but simply mix the ingredients together. Mixed paints are less desirable for airbrushing and for watercolors where fine dispersion is important.

CHARACTERISTICS OF POLYMER FILMS AND PAINTS

After the liquid of a polymer emulsion evaporates, such as with an acrylic polymer, a tough waterproof film formed. Although the chains formed by polymers are broken by ultraviolet light, there is such an overwhelming number of these chains that little or no visible damage occurs from exposure to indoor lighting. Visible damage can occur, however, when the emulsion is exposed to large amounts of direct sunlight outdoors, or when the emulsion has been thinned excessively before application and then exposed to direct sunlight. If a polymer emulsion is applied to a non-oily, absorbent surface, it will remain permanently attached. Although polymer films are quite flexible, there are situations where they can crack. Cracking can occur when a polymer emulsion is overloaded with particulate matter, such as additional pigment or sand, or when a significant amount of polymer is washed out of a paint mixture during the painting process. And an extremely absorbent painting ground can draw out enough polymer from a polymer paint to cause cracking.

The color range of polymer paints is limited for two reasons. The first concerns pH. Alkaline-sensitive pigments cannot be used in the manufacture of acrylics because acrylic emulsions are alkaline. Acid-sensitive pigments cannot be used in vinyl paints because vinyl emulsions are acidic. The second reason is that in polymer emulsions, subtle differences between similarly colored pigments often cannot be seen and are therefore pointless to manufacture.

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ACRYLIC POLYMER EMULSION PAINTS

Liquitex, made by the Binney and Smith Company, and Atelier, a lesser-known acrylic paint made by Chroma Acrylics, are examples of the differing formulations of acrylic paints in the marketplace today. Two different formulations are used for Liquitex, one type for the paint that comes in tubes, and the other for the paint that is available in jars. The paint in tubes is designed to have a thicker consistency and to leave brushstrokes the way oil paint can. The paint that comes in jars is designed to behave more the way an enamel paint would; the paint film tends to level out and the brushstrokes tend to disappear. Most other manufacturers' jars of acrylic paint are made with the same formulation as their tubes. Thinning tube paints will rarely achieve the same effect as Liquitex that comes in jars, and you usually end up with a thinned paint that still leaves brushstrokes.

Atelier is an example of a new type of acrylic for which updated formulations are used. It is designed to appeal to the impasto painter, who desires texture, thickness, and that heavier oil paint appearance. No matter how a manufacturer decides to formulate the consistency of the colors, additives or media are always supplied to alter the consistency to suit the artist's wishes.

ACRYLIC POLYMER SOLUTION PAINTS

There are certain formulations of acrylic polymer, such as Acryloid B-72 manufactured by Rohm and Haas, that form a solution, rather than a emulsion, in mineral spirits. Magna Color, made by Bocour Company, is an example of a paint made with this solution as the binder. Its consistency and general working characteristics are like oil paint, but it dries like acrylic. However, this type of paint has never attained even half the poplarity that acrylic emulsion paints have.

VINYL EMULSION PAINTS

Vinyl emulsions are basically the same as acrylic emulsions. The acrylic polymer has one hydrogen atom replaced by a chloride atom, which results in some slightly different handling properties. Paints made from vinyl emulsions dry very matte and evenly. Acrylic emulsion paints tend to dry spottily with shiny and matte areas, even when a medium is added in an attempt to regulate this effect. Painted surfaces that have variations in surface shine produce the visual illusion of multiple tones of color within one color. This is often a desirable trait for figurative artwork, but is undesirable for most abstract artwork.

It is the matte quality that has made the vinyl emulsion paint Flashe, manufactured by the LeFranc & Bourgeois Company, popular among abstract artists. However, vinyl is said to break down more easily than acrylic when exposed to ultraviolet light and is therefore not recommended for murals where there may be exposure to direct sunlight.

Vinyl and acrylic paints can, in theory, be mixed together. If they are incompatible, the mixture should react immediately, resulting in a "cottage cheese" look, and the mixture will not spread when used. Liquitex colors have, for example, been successfully mixed when Flashe colors, with the one exception of the Flashe black vinyl paint, which will curdle when mixed with an acrylic.

POLYMER EMULSION MEDIUMS

When water is added to a polymer paint it is not only thinned but swollen, and the color appears thick and rich. When the water evaporates, however, the paint shrinks to a thin, dull, and sometimes opaque appearance. A thicker, more transparent, and deeper final appearance can be achieved by thinning the paint with a polymer medium, or with a mixture of water and polymer medium. As the water evaporates, the medium remains to give some bulk to the paint film. The more medium used, however, the more the pigment particles are dispersed and the more transparent the paint film.

Glazes are best produced by mixing a small amount of color in an undiluted medium. A general-purpose medium for thinning colors is a mixture of half water to half medium. Whenever polymer paints are to be thinned greatly with water, some medium should be used because if too much of the paint polymer emulsion is washed away or absorbed by the painting surface during the painting process, the paint film can develop cracks.

Both gloss and matte polymer mediums are available to alter the surface reflection to the desired appearance. Matte mediums are produced by the additive silica, or calcium carbonate, and tend to give a milky appearance to a paint film if used in large amounts. A gloss medium often doubles as a gloss varnish, but this is not true of a matte medium. A hardener must be added to create a matte varnish that will approximate the durability of a gloss varnish.

AUXILIARY PRODUCTS FOR ACRYLIC PAINTING

A number of auxiliary products are available for use in acrylic painting. They are designed to prepare a surface for painting, to slow the drying time of the paints, or to enable the artist to create texture on a surface.

Polymer Gel is a thickening agent that may be added to a polymer medium. For example, sodium polyacrylate can be added to acrylic polymer emulsions. Gels allow for an impasto style of painting with polymer paints. The more gel used, the more transparent the paint film. Gels are resistant to cracking and are excellent as adhesives for collage.
An Acrylic Retarder is either a gel or an additive that evaporates without a trace. It is designed to slow the drying time of acrylic polymer emulsion paints. The recommended amount of retarder to be used varies from manufacturer to manufacturer and if specified amounts are exceeded, the paint film will not form properly. Most retarders, when mixed properly with a color, will slow the drying time to approximately three hours. This allows areas of a painting to be blended or reworked in much the same way as can be done with oil paint.

 

ACRYLIC VARNISH, GLOSS AND MATE

Unprotected polymer paint films are not very durable because they are relatively soft compared to oil paint films and can be marred easily as the result of abrasion. They are also more porous and the pigments and paint film can be affected by air pollution. A varnish can, however, provide the necessary protection. A varnish can also be used to control the surface appearance in terms of matte and gloss. Acrylic polymer solution varnishes, which are dissolved in mineral spirits, are the best protection for acrylic paint films. They are more durable, forming a harder protective film than acrylic emulsion varnishes, which are waterborne. Acrylic polymer solution varnishes also provide better protection against air pollutants because they seal the painting's surface more thoroughly. 

An acrylic polymer emulsion varnish is the same as an acrylic polymer emulsion used as medium, except that the varnish contains a hardener. Unless specified by the manufacturer, an acrylic varnish should not be used as a painting medium. Most manufacturers discourage the thinning of acrylic varnishes, and if diluted with more than 50 percent water, the clarity of the dry varnish film can be seriously affected.

The application of a varnish should be smooth and consistent, and areas that might require more varnish should not be reworked. Reapplying a varnish to a partially dry area can result in streaking, evident brush strokes, and a milky appearance. It is best to wait the hour or two until the varnish dries, and then apply a second coat. Matte varnishes are particularly susceptible to this problem.

The painting surface shine can be regulated not only by choosing a matte or gloss varnish, but also by using a mixture of the two. A matte varnish, despite the hardeners added to it, is not as durable as a gloss varnish. And the matte surface can be rubbed or polished to a shine.

PERMANENCY OF ACRYLIC EMULSION PAINTS

Oil paint has been used for several hundred years, and its range of permanency is well established. Although oil paint is subject to some yellowing and cracking over the centuries, it is still a highly durable medium. Acrylic polymer paint, on the other hand, has been in use only for several decades. Its range of permanency is not established, but is instead implied through accelerated aging tests. Although aging tests have often proven to be quite accurate, they can never take into account all the variables. For example, acrylic and vinyl polymers seem to be more vulnerable to weakening from exposure to ultraviolet light (clear acrylic sheeting used in displays and picture framing does yellow in time from the ultraviolet light in sunlight and fluorescent light) and sulfur air pollutants than previously thought. This is not to say that such paints are unsafe, but rather that all the data are not yet in and there is still some uncertainty as to the actual long-term stability.
 

As an example of this uncertainty, Binny and Smith rate its most permanent colors in Liquitex, artists' acrylic emulsion paints, as having slight or no color changes after the equivalent of one hundred years of indoor museum exposure. Many of these same colors in oil paint often carry a rating that is equivalent to two hundred or more years before any visible changes occur. Oil paint with ratings of seventy five to one hundred years are often classed only as durable. Again, the point here is not that acrylics will not last as long as oil paint, but rather that no one can yet say, even with accelerated aging tests.
 

OIL PAINT AND ACRYLIC PAINT

There is a longstanding debate over whether It IS safe to use oil paint over acrylics because they are made with different paint vehicles. New research seems to indicate that these two types of paint film do adhere quite well to each other, but only more complete testing will tell if the original optimism about the ability of oil paint to bind to acrylic emulsions is justified. Acrylic paint, however, should never be applied over oil paint.

Many people have noticed that oil paint seems to look "richer" than acrylic paint. This is partly due to the fact that oil paint vehicles can hold more pigment than can acrylic emulsions. Also, due to cost, most companies that manufacture acrylic paints use less pure grades of pigment when making colors such as cadmium red and cadmium yellow. (At present, Liquitex's cadmium colors, for example, are made with cadmium-barium pigment instead of pure cadmium. The manufacturer claims that a switch will be made to pure cadmium in the near future.) One company, Winsor & Newton, is now marketing a line of acrylic colors that are made from chemically pure pigments. It uses pure cadmium instead of the cadmium-barium pigment that most other companies use. Whether it makes a great deal of difference if pure pigments are used in acrylic paints seems to be a matter of personal taste. For instance, different types of black pigment such as Mars black and ivory black, which are easily distinguished from one another in an oil paint vehicle, look similar when ground into an acrylic emulsion because of differing refractive properties of oil and acrylic media.

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HAZARDS OF ACRYLIC POLYMER EMULSIONS

The health hazards of the pigments used in acrylic polymer paints are discussed in Pigments, and Hazards, The polymer emulsion itself has hazards of its own that must be considered. Although most major manufacturers have replaced the highly toxic ethylene glycol (wet-edge agent) and toxic preservatives with less hazardous ones in their polymer emulsions, they cannot be considered safe. Some of the polymers evaporate with the water and can be inhaled. Although the amounts are not significant in most painting situations, there are many painters who still do stain painting and color field painting, which involve the use of large amounts of acrylics, and the artist stands directly over the drying paint without any protection.

There are painters and small manufacturers making polymer paints who are not aware of the hazards involved in the manufacturing process and how they can be passed along to other users of their paints. For example, the raw acrylic polymer emulsion used in the manufacture of paint contains significant levels of highly toxic and volatile monomers that must be reduced or eliminated for safe use before handling. Not only can the vapors be hazardous, but mural painters should know about the experience of a well-known mural painter who was hospitalized for acrylic and heavy metal poisoning. She was working outdoors on u mural for the Olympics. The heat of the day apparently opened the pores of her skin, allowing a significant amount of acrylic polymer and pigment to be absorbed. Although polymer paints are not especially dangerous, they are not as safe as the prevailing opinion, and appropriate precautions are necessary.

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