Spray can with enamel paint

Enamel paint is paint that air dries to a hard, usually glossy, finish, used for coating surfaces that are outdoors or otherwise subject to hard wear or variations in temperature; it should not be confused with decorated objects in “painted enamel“, where vitreous enamel is applied with brushes and fired in a kiln. The name is something of a misnomer as in reality, most commercially-available enamel paints are significantly softer than either vitreous enamel or stoved synthetic resins, and are totally different in composition; vitreous enamel is applied as a powder of paste and then fired at high remperature. There is no generally accepted definition or standard for use of the term enamel paint, and not all enamel-type paints may use it.

Typically the term “enamel paint” is used to describe oil-based covering products, usually with a significant amount of gloss in them, however recently many latex or water-based paints have adopted the term as well. The term today means “hard surfaced paint” and usually is in reference to paint brands of higher quality, floor coatings of a high gloss finish, or spray paints. Some enamel paints have been made by adding varnish to oil-based paint.

Although “enamels” and “painted enamel” in art normally refer to vitreous enamel, in the 20th century some artists used commercial enamel paints in art, including Pablo Picasso (mixing it with oil paint), Hermann-Paul and Sidney Nolan. The Trial (1947) is one of a number of works by Nolan to use enamel paint, usually Ripolin, a commercial paint not intended for art, also Picasso’s usual brand.^[1] Some “enamel paints” are now produced specifically for artists.

Uses and categories of enamel paint

• Floor enamel – May be used for concrete, stairs, basements, porches, and patios.
• Fast dry enamel – Can dry within 10–15 minutes of application. Ideal for refrigerators, counters, and other industrial finishes.
• High-temp enamel – May be used for engines, brakes, exhaust, and BBQs.
• Enamel paint is also used on wood to make it resistant to the elements via the waterproofing and rotproofing properties of enamel. Generally, treated surfaces last much much longer and are much more resistant to wear than untreated surfaces.
• Model building – This paint is usually sold in 14 ml tinlets (in the UK) and is available through specialist hobbyshops. Xtracolor and Humbrol are well known UK brands that have a wide range of colours, covering most of the ones used by various armed forces. Testors, a US company, offers the Floquil brand for railroad models, and Pactra, Model Master and Testors brands for aircraft and car models. Liquid enamels are sold in 1/4 to 1 oz. bottles, and some colours are also available in spray cans.

Red acrylic paint

Detail of acrylic painting showing finishes that resemble both oil and watercolor

Acrylic paint is fast drying paint containing pigment suspension in acrylic polymer emulsion. Acrylic paints can be diluted with water, but become water-resistant when dry. Depending on how much the paint is diluted (with water) or modified with acrylic gels, media, or pastes, the finished acrylic painting can resemble a watercolor or an oil painting, or have its own unique characteristics not attainable with other media.

 History

Dr. Otto Rohm invented acrylic resin, which quickly transformed into acrylic paint^[1]. Acrylics were first made commercially available in the 1950s. These were mineral spirit-based paints called Magna^[2] offered by Bocour Artist Colors. Water-based acrylic paints were subsequently sold as “latex” house paints, although acrylic dispersion uses no latex derived from a rubber tree. 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 very best exterior water-based paints are 100% acrylic^[3]. 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 became commercially available in the 1950s, offered by Liquitex, with high-viscosity paints similar to those made today becoming available in the early 1960s ^[4].

 Techniques

Acrylic artist paints may be thinned with water and used as washes in the manner of watercolor paints, but the washes are not re-hydratable once dry. For this reason, acrylics do not lend themselves to color lifting techniques as do gum arabic based watercolor paints.

Fluorescent acrylic paints lit by UV light. Paintings by Beo Beyond

Acrylic paints with gloss or matte finishes are available, although a satin (semi-matte) sheen is most common; some brands exhibit a range of finish (e.g. heavy-body paints from Golden, Liquitex and Winsor & Newton). As with oils, pigment amounts and particle size or shape can naturally affect the paint sheen. Matting agents can also be added during manufacture to dull the finish. The artist can mix mediums to their paints and use topcoats or varnishes to alter or unify sheen if desired.

When dry, acrylic paint is generally non-removable from a solid 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 will result in removal of all of the paint layers, acrylic gesso, etc. Oils can remove acrylic paint from skin^[5].

Only a proper, artist-grade acrylic gesso should be used to prime canvas in preparation for painting with acrylic. It is important to avoid adding non-stable or non-archival elements to the gesso upon application. However, the viscosity of acrylic can successfully be 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.

 Painters and acrylic

Prior to the 19th century, artists mixed their own paints to increase the longevity of the artwork and achieve desired pigment load, viscosity, and to control the use of fillers, if any. While suitable media and raw pigments are available for the individual production of acrylic paint, due to the fast drying time and other technical issues, hand mixing may not be practical.

Acrylic painters modify the appearance, hardness, flexibility, texture, and other characteristics of the paint surface using acrylic media or by simply adding water. Watercolor and oil painters also use various media, but the range of acrylic media is much greater. Acrylics have the ability to bond to many different surfaces, and media can be used to adjust their binding characteristics. Acrylic can be used on paper, canvas and a range of other materials. However, their use on engineered woods such as Medium-density fibreboard can be problematic because of the porous nature of those surfaces^[6]. In these cases it is recommended that the surface should be previously sealed with an appropriate sealer. They can be applied in thin layers or washes creating effects that resemble watercolors and other water-based media. They can also be used to build thick layers of paint: gel and molding paste media are sometimes used to create paintings with relief features that are literally sculptural. Acrylic paints are also used in hobbies such as: train, car, house, 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.

Acrylic paints are the most common paints used in grattage. Grattage is a surrealist technique that became popular with the release of acrylic paint. Acrylics are used for this purpose because they easily scrape or peel from a surface^[7].

 Differences between acrylic and oil paint

The vehicle and binder of oil paints is linseed oil or another drying oil, whereas water serves as the vehicle for an emulsion (suspension) of acrylic polymer that is the binder in acrylic paint. Thus, oil paint is said to be “oil-based”, while 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 in other regards it impedes the 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 generally have some level of toxicity and are often found objectionable. (Relatively recently, water-miscible oil paints have been developed for artists’ use.) Oil paint films can become increasing yellow and brittle with time and lose much of their flexibility in a few decades. Additionally, the rules of “fat over lean” must be employed to ensure the paint films are durable.

Oil paint has a higher pigment load because it is able to absorb substantially more pigment than acrylic because linseed oil has a smaller molecule than does acrylic^[8]. Oil provides a different (less clear) refractive index than acrylic dispersions, imparting a unique “look and feel” to the resultant paint film^[9]. Not all pigments in oil are available in acrylic. For instance, Prussian blue is not generally available due to chemical incompatibility with the acrylic binder. On the other hand there are no fluorescent oil paints like in acrylic.

Due to acrylic’s more flexible nature and more consistent drying time between colors, the painter does not have to follow the “fat over lean” rule of oil painting, where more medium must be applied to each layer to avoid cracking. While canvas needs to be properly sized and primed before painting with oil (otherwise it will eventually rot the canvas), acrylic can be safely applied to raw canvas. The rapid drying of the paint tends to discourage the blending of color and use of wet-in-wet technique as in oil painting. While acrylic retarders can slow drying time to several hours, it remains a relatively fast-drying medium, and the addition of too much acrylic retarder can prevent the paint from ever drying properly.

Although the permanency of acrylics is sometimes debated by conservators, they appear more stable than oil paints. Oil paints fade in color and develop a yellow tint over time; they also begin to crack with age. Acrylic paints have only been around for fifty years, but within this time frame they have yet to alter in ways seen in oil paint. The changes seen in using oil paint is caused by the binder of the paint (linseed oil). Linseed oil dries as an inelastic film. As temperatures rise and fall, this film cracks. 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^[10].

Epoxy

Paints and coatings

Two part epoxy coatings were developed for heavy duty service on metal substrates and use less energy than heat-cured powder coatings. These systems use a 4:1 by volume mixing ratio, and dry quickly providing a tough, protective coating with excellent hardness. Their low volatility and water clean up makes them useful for factory cast iron, cast steel, cast aluminum applications and reduces exposure and flammability issues associated with solvent-borne coatings. They are usually used in industrial and automotive applications since they are more heat resistant than latex-based and alkyd-based paints. Epoxy paints tend to deteriorate, known as chalk out, due to UV exposure.

Polyester epoxies are used as powder coatings for washers, driers and other “white goods”. Fusion Bonded Epoxy Powder Coatings (FBE) are extensively used for corrosion protection of steel pipes and fittings used in the oil and gas industry, potable water transmission pipelines (steel), concrete reinforcing rebar, et cetera. Epoxy coatings are also widely used as primers to improve the adhesion of automotive and marine paints especially on metal surfaces where corrosion (rusting) resistance is important. Metal cans and containers are often coated with epoxy to prevent rusting, especially for foods like tomatoes that are acidic. Epoxy resins are also used for high performance and decorative flooring applications especially terrazzo flooring, chip flooring^[4] and colored aggregate flooring.^[5]

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