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Acrylic paint is a fast-drying paint made of pigment suspended in acrylic polymer emulsion and plasticizers, silicon oils, defoamers, stabilizers, or metal soaps. Acrylic paints are water-soluble, but become water-resistant when dry. Depending on how much the paint is diluted with water, or modified with acrylic gels, mediums, or pastes, the finished acrylic painting can resemble a watercolor, a gouache, or an oil painting, or have its own unique characteristics not attainable with other media.
Otto Röhm invented acrylic resin, which was quickly transformed into acrylic paint. As early as 1934, the first usable acrylic resin dispersion was developed by German chemical company BASF, which was patented by Rohm and Haas. The synthetic paint was first used in the 1940s, combining some of the properties of oil and watercolor. Between 1946 and 1949, Leonard Bocour and Sam Golden invented a solution acrylic paint under the brand Magna paint. These were mineral spirit-based paints. Acrylics were made commercially available in the 1950s.
Following that development, Golden came up with a waterborne acrylic paint called "Aquatec". In 1953, Jose L. Gutierrez produced Politec Acrylic Artists' Colors in Mexico, and Henry Levinson of Cincinnati-based Permanent Pigments Co. produced Liquitex colors. These two product lines were the first acrylic emulsion artists' paints.
Water-based acrylic paints were subsequently sold as latex house paints, as latex is the technical term for a suspension of polymer microparticles in water. Interior latex house paints tend to be a combination of binder (sometimes acrylic, vinyl, pva, and others), filler, pigment, and water. Exterior latex house paints may also be a co-polymer blend, but the best exterior water-based paints are 100% acrylic, due to elasticity and other factors. Vinyl, however, costs half of what 100% acrylic resins cost, and polyvinyl acetate (PVA) is even cheaper, so paint companies make many different combinations of them to match the market.
Soon after the water-based acrylic binders were introduced as house paints, artists and companies alike began to explore the potential of the new binders. Water-soluble artists' acrylic paints were sold commercially by Liquitex beginning in the 1950s, with modern high-viscosity paints becoming available in the early '60s. In 1963, George Rowney (part of Daler-Rowney since 1983) was the first manufacturer to introduce artists' acrylic paints in Europe, under the brand name "Cryla".
Acrylic painters can modify the appearance, hardness, flexibility, texture, and other characteristics of the paint surface by using acrylic mediums or simply by adding water. Watercolor and oil painters also use various mediums, but the range of acrylic mediums is much greater. Acrylics have the ability to bond to many different surfaces, and mediums can be used to modify their binding characteristics. Acrylics can be used on paper, canvas, and a range of other materials; however, their use on engineered woods such as medium-density fiberboard can be problematic because of the porous nature of those surfaces. In these cases, it is recommended that the surface first be sealed with an appropriate sealer. Acrylics can be applied in thin layers or washes to create effects that resemble watercolors and other water-based mediums. They can also be used to build thick layers of paint -- gel and molding paste are sometimes used to create paintings with relief features. Acrylic paints are also used in hobbies such as trains, cars, houses, DIY projects, and human models. People who make such models use acrylic paint to build facial features on dolls  or raised details on other types of models. Wet acrylic paint is easily removed from paintbrushes and skin with water, whereas oil paints require the use of a hydrocarbon.
Acrylics are the most common paints used in grattage, a surrealist technique that began to be used with the advent of this type of paint. Acrylics are used for this purpose because they easily scrape or peel from a surface.
Acrylic artists' paints may be thinned with water or acrylic medium and used as washes in the manner of watercolor paints, but unlike watercolor the washes are not rehydratable once dry. For this reason, acrylics do not lend themselves to the color lifting techniques of gum arabic-based watercolor paints. Instead, the paint is applied in layers, sometimes diluting with water or acrylic medium to allow layers underneath to partially show through. Using an acrylic medium gives the paint more of a rich and glossy appearance, whereas using water makes the paint look more like watercolor and have a matte finish.
Acrylic paints with gloss or matte finishes are common, although a satin (semi-matte) sheen is most common. Some brands exhibit a range of finishes (e.g. heavy-body paints from Golden, Liquitex, Winsor & Newton and Daler-Rowney); Politec acrylics are fully matte. As with oils, pigment amounts and particle size or shape can affect the paint sheen. Matting agents can also be added during manufacture to dull the finish. If desired, the artist can mix different media with their paints and use topcoats or varnishes to alter or unify sheen.
When dry, acrylic paint is generally non-removable from a solid surface if it adheres to the surface. Water or mild solvents do not re-solubilize it, although isopropyl alcohol can lift some fresh paint films off. Toluene and acetone can remove paint films, but they do not lift paint stains very well and are not selective. The use of a solvent to remove paint may result in removal of all of the paint layers (acrylic gesso, et cetera). Oils and warm, soapy water can remove acrylic paint from skin. Acrylic paint can be removed from non-porous plastic surfaces, such as miniatures or models using certain cleaning products such as Dettol (containing chloroxylenol 4.8% v/w).
An acrylic sizing should be used to prime canvas in preparation for painting with acrylic paints, to prevent Support Induced Discoloration (SID). Acrylic paint contains surfactants that can pull up discoloration from a raw canvas, especially in transparent glazed or translucent gelled areas. Gesso alone will not stop SID; a sizing must be applied before using a gesso.
The viscosity of acrylic can be successfully reduced by using suitable extenders that maintain the integrity of the paint film. There are retarders to slow drying and extend workability time, and flow releases to increase color-blending ability.
Commercial acrylic paints come in two grades by manufacturers:
The vehicle and binder of oil paints is linseed oil (or another drying oil), whereas acrylic paint has water as the vehicle for an emulsion (suspension) of acrylic polymer, which serves as the binder. Thus, oil paint is said to be "oil-based", whereas acrylic paint is "water-based" (or sometimes "water-borne").
The main practical difference between most acrylics and oil paints is the inherent drying time. Oils allow for more time to blend colors and apply even glazes over underpaintings. This slow-drying aspect of oil can be seen as an advantage for certain techniques, but it impedes an artist trying to work quickly. The fast evaporation of water from regular acrylic paint films can be slowed with the use of acrylic retarders. Retarders are generally glycol or glycerin-based additives. The addition of a retarder slows the evaporation rate of the water.
Oil paints may require the use of solvents such as mineral spirits or turpentine to thin the paint and clean up. These solvents generally have some level of toxicity and can be found objectionable. Relatively recently, water-miscible oil paints have been developed for artists' use. Oil paint films can gradually yellow and loose their flexibility over time creating cracks in the paint film ensuring the "fat over lean" rule must be observed to ensure its durability.
Oil paint has a higher pigment load than acrylic paint. As linseed oil contains a smaller molecule than acrylic paint, oil paint is able to absorb substantially more pigment. Oil provides a refractive index that is less clear than acrylic dispersions, which imparts a unique "look and feel" to the resultant paint film. Not all the pigments of oil paints are available in acrylics and vice versa, as each medium has different chemical sensitivities. Some historical pigments are alkali sensitive, and therefore cannot be made in an acrylic emulsion; others are just too difficult to formulate. Approximate "hue" color formulations, that do not contain the historical pigments, are typically offered as substitutes.
Due to acrylic paint's more flexible nature and more consistent drying time between layers, an artist does not have to follow the same rules of oil painting, where more medium must be applied to each layer to avoid cracking. It usually takes 15-20 minutes for one to two layers of acrylic paint to dry. Although canvas needs to be properly primed before painting with oils to prevent the paint medium from eventually rotting the canvas, acrylic can be safely applied straight to the canvas. The rapid drying of acrylic paint tends to discourage blending of color and use of wet-in-wet technique as in oil painting. Even though acrylic retarders can slow drying time to several hours, it remains a relatively fast-drying medium and adding too much acrylic retarder can prevent the paint from ever drying properly.
Meanwhile, acrylic paint is very elastic, which prevents cracking from occurring. Acrylic paint's binder is acrylic polymer emulsion - as this binder dries, the paint remains flexible.
Another difference between oil and acrylic paints is the versatility offered by acrylic paints. Acrylics are very useful in mixed media, allowing the use of pastel (oil and chalk), charcoal and pen (among others) on top of the dried acrylic painted surface. Mixing other bodies into the acrylic is possible--sand, rice, and even pasta may be incorporated in the artwork. Mixing artist or student grade acrylic paint with household acrylic emulsions is possible, allowing the use of premixed tints straight from the tube or tin, and thereby presenting the painter with a vast color range at their disposal. This versatility is also illustrated by the variety of additional artistic uses for acrylics. Specialized acrylics have been manufactured and used for linoblock printing (acrylic block printing ink has been produced by Derivan since the early 1980s), face painting, airbrushing, watercolor-like techniques, and fabric screen printing.
Another difference between oil and acrylic paint is the cleanup. Acrylic paint can be cleaned out of a brush with any soap, while oil paint needs a specific type to be sure to get all the oil out of the brushes. Also, it is easier to let a palette with oil paint dry and then scrape the paint off, whereas one can easily clean wet acrylic paint with water.
The striking difference is that acrylic is opaque, whereas watercolor is translucent in nature.