Acrylic, Oil, and Mural Painting Techniques
Acrylic Painting
Acrylics appeared in the mid-nineteenth century, but it was not until the 1930s when they became commercially available. American artists were among the first to use acrylic paint, incorporating it into contemporary art. Gradually, artists became more aware of the many technical possibilities of this medium, such as the stability of the colors and, most importantly, the speed of drying. Acrylic has similarities with oil in color stability and texture, but a huge advantage in terms of drying almost immediately. Currently, acrylic has a large following, especially among those doing large-scale works. However, many artists combine both mediums, not abandoning oil entirely.
Features
Acrylic paints are a derivative of the plastics industry, similar to wall paints, and use pigments that can be natural or synthetic. The pigments used for acrylics are the same as those used for oil. The only difference is the binder used: oil in oil paints and a transparent aqueous polymer resin emulsion in acrylics. This explains why acrylics are so resistant, acting as a plastic coating once dry that is impossible to remove. Acrylic paints are diluted with water, unlike oil, which is diluted with oil-based solvents. While it is essential to dilute acrylics with water for certain techniques, they can also be used directly from the tube. Additives can be mixed in to give consistency or a matte or glossy finish. Acrylics can be applied with a spatula in thick layers, diluted with water for a watercolor effect, or mixed with different mediums to achieve various textures.
Acrylics are ideal for large paintings due to their versatility and fast drying, allowing for continuous work without long waits.
They can be used in combination with other materials for painting or drawing to create mixed media works.
Key Features of Acrylic
- Light, giving vibrant color.
- Wide ranges of transparency and density.
- Fluency in mixtures.
- Drying and shrinkage, allowing for large fillings that dry with stability.
- Light stability, meaning high resistance to color degradation due to the medium protecting the pigments.
- Does not yellow or age.
- Quick drying, allowing for overlapping colors and fast work.
- Can be sprayed, scraped, and mixed with other materials.
- Can create smooth surfaces.
Presentation
- Tubes
- Jars
Supports
Paper, board, canvas, wood. Do not use on greasy surfaces or surfaces prepared for oil painting.
Palettes
Plastic, glass, or wood with acrylic primer to prevent sticking. (Do not use untreated wood as the paint will adhere to it.)
Brushes
Bristle brushes for oils or synthetic brushes. Spatulas can also be used.
Techniques
Washes, spraying, tapping, and creating textures.
Oil Painting
Oil painting, as an art form, is known for using oils combined with other substances to create a suitable painting medium. The term “oils” also refers to paintings created using oil paint. Oil painting has been known since ancient times and was widespread among artists of the Middle Ages, especially when combined with egg tempera or fresco. Its use became widespread in Europe from the sixteenth century onward.
Features
Oil paint is made of ground pigments and very drying oils, such as linseed oil, or semi-drying oils like walnut or poppy, which dry by oxidation. The most commonly used oil is linseed oil, often mixed with mineral pigments that provide the color. Both its density and texture give oil paint the advantage of staying wet for a long time, allowing the painter to clean their mistakes with a spatula and start over. Unlike fresco or tempera, which dry quickly, the moisture of oil allows for extended working sessions. Oil colors do not change when dry, but over the years, they tend to darken due to the oxidation of the oil. The drying time of oil depends on its color (earth colors dry fastest). Many manufacturers use accelerators or retardants to match the drying time of different colors. In general, oil drying takes between 2 and 10 days, depending on the weather. Oil painting can be worked in two ways: with fine or transparent glazes or by impasto, which gives greater opacity. Color differences also vary the degree of opacity. Oil can be worked wet-on-wet, allowing for fades, or by letting layers dry and working wet-on-dry. Oil paint is often diluted with turpentine to make it thinner. Ideally, mix the oil with turpentine, oil, and Damar varnish to give the desired body.
Materials
Oil paint is sold in tubes of different colors (8 or 9 tubes are enough, as they mix well). There are different brands of oil paints, varying in quality and price.
Solvents and Thinners
White spirit is the most practical solvent. It is also used for cleaning brushes and materials. It is highly flammable and must be handled carefully. Turpentine is of good quality, mixes well with oil, and evaporates uniformly. It has been used as a substitute for turpentine for years. It has a less intense smell, does not produce allergic reactions, and is more economical. There is also turpentine simile, which is more toxic and has a much stronger smell.
Turpentine: It is still used instead of white spirit. Its only advantage is that it evaporates faster. Adding too much turpentine to oil can soften old paint.
Supports
The ideal support is canvas, but wood, metal, or cardboard can also be used. The best linen cloth is stretched on a wooden frame, treated with animal glue primer (rabbit glue and opaque white). With the appropriate primer, wood panels provide a more permanent base than canvas.
Brushes
The most appropriate brushes are bristle, being tough and durable. Fine hair brushes can also be used for finishing touches. Common brush types include:
- Flat
- Round
- Filberts (a mixture of flat and round, used for blending)
- Square (flat and short, for impasto)
- Fan (for very soft strokes)
Palette knives can be used for impasto and textures. They are also used to mix colors on the palette.
Palettes
Wooden palettes with a thumb hole are used. (They usually do not have wells like watercolor palettes.)
Techniques
Usually, one begins with a preliminary drawing in charcoal or graphite. Subsequently, shapes and colors are outlined with paint diluted with turpentine. Layers of color should be applied with increasing amounts of paint to avoid cracking.
Other Techniques
Alla Prima: A direct painting method that is safe and easy. The entire area of the painting is applied in a single session, requiring accurate strokes. It is used to highlight the expressiveness of the work, using few mixed colors. The entire painting is worked on at the same time, avoiding drying problems as everything is wet. The first painters to use this technique were the Impressionists and English landscape artists.
Glazes: This technique was most commonly used during the Renaissance and by later artists like Rembrandt. Glazing involves applying very thin layers of paint so that the underlying layer is transparent, and the resulting color is a mixture of the glaze and the underlying color. To create a glaze, the lower layer must be completely dry.
Impasto: Using very thick paint (directly from the tube) or mixing it with a special impasto medium, sand, sawdust, or marble powder to create textures. It can be worked with a brush or palette knife. (Vincent van Gogh)
Advantages of Oil Painting
- High quality and sharpness.
- Allows for a variety of techniques.
- Suitable for large sizes.
- Wide range of colors.
Disadvantages
- Very slow drying process.
- Colors darken over time.
- Cracking can occur if proper working methods are not followed.
Mural Painting
The first paintings in history, cave paintings, were executed on the rock walls of Paleolithic caves using natural pigments and resin binders. Painting on walls dominated during the Romanesque period but declined in the Gothic period as walls were replaced by stained glass, leading to the rise of panel painting. During the Renaissance, there were significant murals, including frescoes by Raphael in the Stanze of the Vatican and the work of Michelangelo Buonarroti in the Sistine Chapel. Subsequently, mural painting has been limited to building walls and ceilings, with notable decorations of the Baroque and Rococo periods. These often combined with stucco reliefs, giving rise to illusionistic, impressionistic creations.
Mural painting has never completely disappeared, as seen in the work of Hispanic muralists. The most famous were Diego Rivera, David Alfaro Siqueiros, Jose Clemente Orozco in Mexico, and Teodoro Núñez Ureta in Peru.
Street graffiti, at least in its most artistic and monumental forms, could be considered a contemporary urban form of mural painting.
Features
The mural is mostly decorative but also serves didactic purposes. The mural should contain a narrative. Therefore, it is often described as a still movie.
Main Features of Mural Painting
- Monumentality, determined not only by the size of the wall but also by the composition of the image.
- Polyangularity, breaking the plane of the wall space.
Techniques
Except in prehistory, murals are not painted directly on the wall but on a thin interlayer. The main technique used throughout the centuries for murals is fresco. The surface is prepared with several layers of plaster: first, a rough plaster called arriccio, then a thin layer of fine sand and lime called intonaco. The pigment dissolved in limewater is then applied to the still-wet wall. Murals can be produced in different ways:
- Fresco: Paint is applied to the still-wet plaster of the wall.
- Secco: Paint is applied to a dry wall.
- Encaustic: A technique used by the Romans, where colors are dissolved in a mixture of beeswax and resin, applied hot, and set on the wall as they dry.
It is possible to paint in tempera on walls and ceilings. In this case, one must wait until the plaster is dry. In the early twentieth century, acrylic became a prominent material, used by Mexican muralists like Rivera and Orozco. Today, materials are used that allow for long-lasting murals without excessive maintenance, especially when located outdoors. Other widely used techniques include sgraffito on colored cement, ceramic murals, stone mosaics, and tiles.
Traditional Mural Painting: Buon Fresco
Fresco has been the primary technique of mural painting. Unlike other procedures, the wall must be damp when painting. The technique involves applying pigments dissolved in pure water or limewater to the wall, which must be prepared with a mortar of lime and sand: one layer of 3 parts sand to 1 part lime. The wall must be damp. The process is based on the carbonation of lime. When the wall dries, the water evaporates, and the lime absorbs carbon dioxide from the air, producing calcium carbonate, which acts as a crystal. The wall and color become an even surface with all elements integrated, insoluble, and unalterable. It is the most durable mural painting technique. The application of colors must be done quickly and confidently, as the wall must be damp and cannot be retouched. (Goya)
Dry Mural Painting
Dry mural painting is used on dry walls. Its most common use is for corrections. Entire paintings can also be made using this technique, but with new procedures like acrylic paint, it is no longer widely used.
Variants of the Dry Technique
- Lime Secco: Uses lime diluted in water as a color binder. It is less durable and light-resistant than others.
- Tempera: Primarily used for retouching frescoes. Generally used in small sizes and rarely used today.
- Oil: Has been used with a spatial comparison of the wall (like a sealant). Goya used it in the Aula Dei and in the Quinta del Sordo.