An ink is a liquid containing various pigments and/or dyes used for coloring a surface to render an image or text. Common perceptions consider ink for use in drawing or writing with a pen or brush. However, inks are used most extensively in printing.
Types of Ink
Early varieties of ink include Indian ink, various natural dyes made from metals, the husk or outer covering of nuts or seeds, and sea creatures like the squid (known as sepia). India ink is black and originated in Asia. Walnut ink and iron-gall nut ink were made and used by many of the early masters to obtain the golden brown ink used for drawing.
Pigmented Inks
Pigmented inks contain other agents to ensure adhesion of the pigment to the surface and prevent its being removed by mechanical abrasion. These materials are typically referred to as resins (in solvent-based inks) or binding agents (in water-based inks).
Pigmented inks have the advantage when printing on paper that the pigment stays on the surface of the paper. This is desirable, because when more ink stays on the surface of the paper, less ink needs to be used to create the same intensity of color.
Dyes in Inks
Dyes, however, are generally much stronger and can produce more color of a given density per unit of mass. However, because dyes are dissolved in the liquid phase, they have a tendency to soak into paper, thus making the ink less efficient and also potentially allowing for the ink to bleed at the edges, producing unsightly and poor-quality printing.
To circumvent this problem, dye-based inks are made with solvents that dry rapidly or are used with quick-drying methods of printing, such as blowing hot air on the fresh print. Other methods to resolve this include harder paper sizing and more specialized paper coatings. The latter is particularly suited to inks that are used in non-industrial settings (and thus must conform to tighter toxicity and emission controls), such as ink jet printer inks, include coating the paper with a charged coating. If the dye has the opposite charge, then it is attracted to and retained by this coating, while the solvent soaks into the paper. Cellulose, the material that paper is made of, is also naturally charged, and so a compound that complexes with both the dye and the paper surface aids retention at the surface. Such a compound in common use in ink-jet printing inks is polyvinyl pyrrolidone.
An additional advantage of dye-based ink systems is that the dye molecules interact chemically with other ink ingredients. This means that they can benefit more than pigmented ink from optical brighteners and color-enhancing agents designed to increase the intensity and appearance of dyes. Because dyes get their color from the interaction of electrons in their molecules, the way in which the electrons can move is determined by the charge and extent of electron delocalisation in the other ink ingredients. The color emerges as a function of the light energy that falls on the dye. Thus, if an optical brightener or color enhancer absorbs light energy and emits it through or with the dye, the appearance changes, as the spectrum of light re-emitted to the observer changes.
A disadvantage of dye-based inks is that they can be more susceptible to fading, especially when exposed to ultraviolet radiation as in sunlight.
In biology, pigment is any material resulting in color in plant or animal cells which is the result of selective absorption. Some biological material has so-called structural color, which is the result of selective reflection or iridescence, usually done with multi-layer structures. Unlike structural color, pigment color is the same for all viewing angles. Nearly all types of cells, such as skin, eyes, fur and hair contain pigment. Butterfly wings typically contain structural color, although many of them contain pigment as well. Creatures that have deficient pigmentation are called albinos.
Because pigment color is the result of selective absorption, there is no such thing as white pigment. A white object is simply a diffuse reflecting object which does not contain any pigment.
In the coloring of paint, ink, plastic, fabric and other material, a pigment is a dry colorant, usually an insoluble powder. There are both natural and synthetic pigments, both organic and inorganic ones. Pigments work by selectively absorbing some parts of the visible spectrum (see light) whilst reflecting others.
A distinction is usually made between a pigment, which is insoluble, and a dye, which is either a liquid, or is soluble. There is no well-defined dividing line between pigments and dyes, however, and some coloring agents are used as both pigments and dyes. In some cases, a pigment will be made by precipitating a soluble dye with a metallic salt. The resulting pigment is called a "lake".
Painting Pigments
Alizarin (Alizarin, or 1,2-dihydroxyanthraquinone, is the red dye originally derived from the root of the madder plant. In 1869, it became the first natural pigment to be duplicated synthetically.)
Bone black (also known as bone char) (Bone char, also known as bone black or animal charcoal, is a granular black material produced by calcining animal bones: the bones are heated to high temperatures in the absence of air to drive off volatile substances. It consists mainly of calcium phosphate and a small amount of carbon. Bone char has a very high surface area and a high absorptive capacity for lead, mercury, and arsenic.)
Cadmium pigments (About 2/3 to 3/4 of Cadmium produced worldwide is used in the production of Ni-Cd Batteries. About half the remaining consumption or 2,000 tons annually, is used to produce colored Cadmium pigments. The principal pigments are a family of yellow/orange/red cadmium sulfides and sulfoselenides. Brilliantly colored, with good permanence and tinting power, Cadmium Yellow, Cadmium Orange, and Cadmium Red are familiar artist colors, but of little use in architectural paints.)
Carbon black (Soot, also called lampblack or carbon black, is a dark powdery deposit of unburned fuel residues, usually composed mainly of amorphous carbon, that accumulates in chimneys, automobile mufflers and other surfaces exposed to smoke—especially from the combustion of carbon-rich organic fuels in the lack of sufficient oxygen. Lampblack has been used as the black pigment in paints and inks since prehistoric times, and is still widely used in printing inks, toners for xerography and laser printers, and in chemical industry.)
Cerulean blue (Cerulean blue is a cerulean (light blue or azure) pigment used in artistic painting. It is particularly valuable for painting atmospheric shades because of the purity of the blue (specifically the lack of greenish hues). The pigment is regarded as permanent: in oil, no other blue pigment retains color as well.)
Chromium pigments (Chromium is a steel-gray, lustrous, hard metal that takes a high polish, is fusible with difficulty, and is resistant to corrosion and tarnishing.)
Cobalt pigments (Cobalt is a hard ferromagnetic silver-white element.)
Crimson (A deep red color tinged with blue; also, red color in general; deep red color. Traditionally, it is the color of blood.)
Fugitive pigments (Fugitive pigments, in painting, are non-permanent pigments (pigments that lighten in what is understood, said or defined 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.)
Indigo (Indigo is the color of light between 440 to 420 nanometers in wavelength, placing it between blue and violet. Like many other colors - the plant named indigo once used for dyeing cloth.)
Ivory black (Ivory black is an artistic pigment formerly made by grinding charred ivory in oil.)
Lead pigments (A soft, heavy, toxic and malleable poor metal, lead is bluish white when freshly cut but tarnishes to dull gray when exposed to air.)
Mars black
Naples yellow
Phthalocyanine (A phthalocyanine is a macrocyclic compound having an alternating nitrogen atom-carbon atom ring structure.)
Prussian blue (Prussian blue is a blue pigment used in paints and formerly in blueprints. It has several different chemical names, these being iron (III) ferrocyanide, ferric ferrocyanide, iron (III) hexacyanoferrate (II), and ferric hexacyanoferrate.)
Quinacridone
Red ochre (Red ochre and yellow ochre (pronounced OAK-ur, from the Greek ochros, yellow) are pigments made from naturally tinted clay. It has been used worldwide since prehistoric times. Chemically, it is anhydrous iron (III) oxide. Ochres are non-toxic, and can be used to make an oil paints that dry quickly and cover surfaces thoroughly.)
Sanguine (Sanguine - a red earth pigment used in the manufacture of artists chalks or pastels. First used by Renaissance artists. Still used by manufacturers such as Conté; to name reddish-brown chalks, colored with Iron Oxide.)
Sienna (Sienna is a form of limonite clay most famous in the production of oil paint pigments. Its yellow-brown color comes from ferric oxides contained within. As a natural pigment, it (along with its chemical cousins ochre and umber) was one of the first pigments to be used by humans, and is found in many cave paintings. Sienna, in and of itself, is sometimes referred to as "raw sienna", in order to differentiate it from "burnt sienna", which is a more common pigment than the raw form. The difference is in the process applied to burnt sienna, which is raw sienna heated to remove the water from the clay and redden its brownish color.)
Titanium dioxide (Titanium dioxide is the most widely used white pigment because of its brightness and very high refractive index (n=2.4), in which it is surpassed only by diamond.)
Ultramarine (Ultramarine is a blue pigment, consisting essentially of a double silicate of aluminum and sodium with some sulfides or sulfates, and occurring in nature as a proximate component of lapis lazuli.)
Venetian red
Yellow ochre (red ochre and yellow ochre (pronounced OAK-ur, from the Greek ochros, yellow) are pigments made from naturally tinted clay. It has been used worldwide since prehistoric times. Chemically, it is anhydrous iron (III) oxide. Ochres are non-toxic, and can be used to make an oil paints that dry quickly and cover surfaces thoroughly.)
Zinc white
Paint is the general term for a family of products used to protect and add color to an object or surface by covering it with a pigmented coating. As a verb, painting is the application of paint. One who paints is called a painter.
Paint is very common and is applied to almost every kind of object. It is a method of producing art, an industrial coating, a driving aid (lane markings), a preservative (rust-prone steel auto bodies), on interior walls, on exterior surfaces exposed to weather, and myriad other uses.
With art, it has also been used for centuries in the creation of great works, such as Leonardo da Vinci's Mona Lisa and Vincent Van Gogh's Starry Night. There is a wide variety of artists' paints available for the professional or amateur artist.
Components
There are generally three parts to a paint: binder, diluent and additives. However, only one of these components, the binder, is absolutely required. The binder is that part of the vehicle which eventually solidifies to form the dried paint film. The diluent serves to adjust the viscosity of the paint. It is volatile and does not become part of the paint film. Anything else is an additive.
Typical binders include synthetic or natural resins such as acrylics, polyurethanes, polyesters, melamines, oils, or latex. Typical diluents include organic solvents such as alcohols, ketones, esters, glycol ethers, and the like. Water is a common diluent. Sometimes volatile low-molecular weight synthetic resins also serve as diluents. Typical additives include pigments, dyes, catalysts, thickeners, stabilizers, emulsifiers, texturizers, adhesion promoters, flatteners (de-glossing agents), and the like.
After application, the paint solidifies and becomes tack-free. Depending on the type of binder, this hardening may be a result of curing (polymerization), evaporation, or even cooling. In oil-based paint, curing takes the form of oxidation, for example oxidation of linseed oil to form linoxin to create a varnish. Other common cured films are prepared from cross linkers, such as polyurethane or melamine resins, reacted with acrylic polyester or polyurethane resins, often in the presence of a catalyst which serves to make the curing reaction proceed more quickly or under milder conditions. These cured-film paints can be either solvent-borne or waterborne. Other waterborne paints are emulsions of solid binders in water. When the diluent evaporates, the molecules of the binder coalesce to form a solid film. Still other films are formed by cooling of the binder. For example, encaustic or wax paints are liquid when warm, and harden upon cooling.
Art
Since the time of the Renaissance, siccative (drying) oil paints, primarily linseed oil, have been the most commonly used kind of paints in fine art applications; oil paint is still common today. However, in the 20th century, water-based paints, including watercolors and acrylic paints, became very popular with the development of latex and acrylic pigment suspensions. Watercolor is a painting technique making use of water-soluble pigments that are either transparent or opaque and are formulated with gum to bond the pigment to the paper. Although the grounds used in watercolor painting are varied, the most common is paper. Others include papyrus, bark papers, plastics, leather, fabric, wood, and canvas. Acrylic paint is fast-drying paint containing pigment suspended in an acrylic polymer resin. Acrylic paints can be diluted with water, but become water-resistant when dry. Depending on how much the paint is diluted (with water), the finished acrylic painting can resemble a watercolor or an oil painting. Milk paints (also called casein), where the medium is derived from milk, were popular in the 19th century and are still available today. Egg tempera (where the medium is egg yolk) is still in use as well, as are encaustic wax-based paints. Gouache is a variety of watercolor paint which was also used in the Middle Ages and Renaissance for manuscript illumination. The pigment was often made from ground semiprecious stones such as lapis lazuli and the binder made from either gum arabic or egg white. Gouache is commercially available today. Poster paint has been used primarily in the creation of student works, or by children.
Pigment
Pigments, usually insoluble powders, are used both to provide color, and to make paint opaque, thus protecting the substrate from the harmful effects of ultraviolet light while also increasing a paint's hiding power.
Lead paint White pigment does not add color, but serves the very important function of increasing opacity and making the paint resistant to UV radiation. For centuries, the primary white pigment in paints was lead white (basic lead carbonate, 2PbCO3·Pb(OH)2), one of the oldest pigments known. The problem with lead white is that it is extremely toxic.
It wasn't until the middle of the 20th century that white lead was generally replaced by a less toxic substitute, titanium white, which was first used in paints in the 19th century. The titanium white used in most paints today is actually a mixture of titanium dioxide (pure titanium white) and zinc oxide (zinc white).
Application
Paint can be applied as a liquid, as a solid, or as a gaseous suspension. Techniques vary depending on the practical or artistic results desired.
In the liquid application, paint can be applied by direct application using brushes, paint rollers, blades, other instruments, or body parts. Examples of body parts include finger-painting, where the paint is applied by hand, whole-body painting (popular in the 1960's avant-garde movement), and cave painting, in which a pigment (usually finely-ground charcoal) is held in the mouth and spat at a wall (NOTE: DO NOT DO THIS with modern paints, they are highly toxic and this might cause death or permanent injury).
Paint may also be applied by flipping or spraying the paint, dripping, or by dipping an object in paint.
As a solid (usually in industrial and automotive applications), the paint is applied as a very fine powder, then baked at high temperature. This melts the powder and causes it to adhere (stick) to the surface. The reasons for doing this involve the chemistries of the paint, the surface itself, and perhaps even the chemistry of the substrate (the overall object being painted).
As a gas or as a gaseous suspension, the paint is suspended in solid or liquid form in a gas that is sprayed on an object. The paint sticks to the object. The reasons for doing this include:
the application mechanism is air and thus no solid object ever touches the object being painted;
the distribution of the paint is very uniform so there are no sharp lines
it is possible to deliver very small amounts of paint or to paint very slowly;
a chemical (typically a solvent) can sprayed along with the paint to dissolve together both the delivered paint and the chemicals on the surface of the object being painted;
some chemical reactions in paint involve the orientation of the paint molecules.
Paint is often applied to walls with a roller. Rollers generally have a handle that allows for different lengths of poles which can be attached to allow for painting at different heights. Generally, roller application takes two coats for even color. A roller with a thicker nap is used to apply paint on uneven surfaces. Edges are often finished with an angled brush.
Product Variants
Wood stain is a type of paint that is very "thin," that is, low in viscosity, and formulated so that the pigment penetrates the surface rather than remaining in a film on top of the surface. Stain is predominantly pigment or dye and solvent with little binder, designed primarily to add color without providing a surface coating.
Varnish and shellac provide a protective coating without changing the color. They are paints without pigment.
Lacquer is usually a fast-drying solvent-based paint or varnish that produces an especially hard, durable finish.
An enamel paint is a paint that dries to an especially hard, usually glossy, finish. Enamel can be made by adding varnish to oil-based paint.
Finger-paint
Inks are similar to paints, except they are typically made using dyes exclusively (no pigments), and are designed so as not to leave a thick film of binder.
Titanium Dioxide is extensively used for both house paint and artist's paint, because it is permanent and has good covering power. Titanium oxide pigment accounts for the largest use of the element. Titanium paint is an excellent reflector of infrared, and is extensively used in solar observatories where heat causes poor seeing conditions.
History
Ancient painted walls, to be seen at Dendara, Egypt, although exposed for many ages to the open air, still possess a perfect brilliancy of color, as vivid as when painted, perhaps 2000 years ago. The Egyptians mixed their colors with some gummy substance, and applied them detached from each other without any blending or mixture. They appeared to have used six colors: white, black, blue, red, yellow, and green. They first covered the field entirely with white, upon which they traced the design in black, leaving out the lights of the ground color. They used minimum for red, and generally of a dark tinge.
Pliny mentions some painted ceilings in his day in the town of Ardea, which had been executed at a date prior to the foundation of Rome. He expresses great surprise and admiration at their freshness, after the lapse of so many centuries.
