I am often asked about the differences between oils and acrylics and much of my instruction on painting materials and techniques is focused on this fundamental topic. Once you understand the working characteristics of these two superb media, it will help you decide which one is best suited for you, or, if you are like me and paint in both media, then which one is best suited for the particular expression at hand.
Oil paints have been around for centuries and have passed the test of time. The vast majority of the greatest paintings in the Western World have been done in this medium for over 500 years. Acrylics have only been available since the middle of the 20th century but it appears that this medium is also here to stay, and for good reason.
Initially, acrylics were offered as a substitute for oil paints, just as synthetic resin paints, like latex, have replaced oil paints for the most part in commercial wall painting applications; and for the same reasons: Synthetic polymer paints dry fast and clean up easily with water; plus, they don’t smell as bad.
What we have learned since their introduction is that acrylics present an interesting alternative to oils, but not a good substitute in many regards. Oils do some things extremely well that acrylics are not as well suited for. On the other hand, acrylic paints and mediums have opened up a whole new world of techniques and creative possibilities.
Here then, is a summary of the differences between the two media:
Slow vs Fast: Oils dry slower than acrylics. This means more time for blending and creating various ‘painterly’ effects in your compositions. Oil paints are perfect for the classic ‘Wet in Wet’ style of painting or for precise and carefully blended effects.
With acrylics, you can over-paint within minutes without picking up the underpainting, but if you spend too much time trying to mix and blend them, they will lift and create streaks and ‘marring.’ Nevertheless, a multilayered composition full of glazes, veils and impasto painting, and even textured effects, including mixed media and collage techniques, can be accomplished in one sitting. There are slower drying acrylics on the market as well as retardant mediums you can mix with the paint to increase blending time.
An example of a painting sequence in acrylics, that can be done in one sitting, if you paint fast enough. This would be 3 or 4 separate sittings in oils as each layer needs to dry before adding the next.
Oxidation vs Evaporation: Oils polymerize (dry) thru a complicated chemical reaction that involves oxidation. They absorb oxygen and actually expand at a certain stage of the drying process. That is why it is not good to paint a fast drying color over a slow drying color.
Acrylics dry as water evaporates from the paint film, usually within a few minutes depending on the thickness of the layer and the relative humidity of the surrounding air. The paint layer actually shrinks once the water is evaporated.
Variable vs Uniform: With oil paints, different pigments dry at different rates, some slower than others, anywhere between a couple of days and a few weeks. In addition, there are varying degrees of stiffness and flexibility in the dried films. Moreover, the ‘fat’ colors (higher oil to pigment ratio) will have a more glossy finish than the ‘leaner’ ones. All of this requires the oil painter to be familiar with the different properties and drying characteristics of the assorted pigments if they are concerned with permanence, particularly if they are painting in layers.
All acrylics colors and mediums dry at the same rate and are all intermixable with all other colors and mediums without issue. Simple.
It is a good idea to paint out swatches like this of all your oil paints to familiarize yourself with the various drying rates of the different hues.
Smooth vs Bumpy: Oil paint has a smoother surface texture and the medium itself is more transparent than acrylic polymer resin. In general, colors in oils are clearer and more ‘luminous.’ The surface of acrylic paint is more rough and porous by comparison. That is one of the reasons why acrylic paint looks ‘softer’ and more muted in its color effects than oils. It is also one of the main reasons why oils adhere better to acrylics, which have more ‘tooth’, than the other way around. So, paint oils over acrylics, if you must, but not vice versa.
More vs Less: Oil paints have a higher pigment load than acrylic paints for the most part and so the colors are more intense. This also means that it usually requires less paint to achieve a particular tint or shade when mixing paints, which is significant because good quality oil paints are generally more expensive than good acrylic paints. Also, several pigments are not compatible with the alkaline environment of acrylic resin and so most manufacturers are able to offer a greater range of hues in oils. The gap is closing somewhat in recent years with the development of many synthetic pigments that are used in both media.
Furthermore, the variation of color effects is more pronounced in oils: the transparent colors are more so, clearer and shinier, and the opaque colors are more thick and dense than their acrylic counterparts.
Same/Different vs Different/Same: Oil paints look the same when they are dry as they do wet; the colors, shade, and texture remain unchanged. With age on the other hand, Oils paints turn more yellow/brown and become more transparent. This is the reason why the oil painters of the early Renaissance painted their lights thinly, over a smooth white gesso ground, and their darks, especially the cool ones, very thick. In this way as the paint warmed in hue and became more transparent, these effects were compensated for, ensuring that the paintings would retain their compositional integrity even centuries later - brilliant.
Acrylics dry darker initially, because the water in the paint, which is reflective, evaporates. Acrylic paint also shrinks and flattens out somewhat because of the water loss, so some of the texture and brushing effects are lost. This shrinking is also the reason why flexible supports like paper and unstretched canvas will warp when the acrylic paint contracts. However, once dry, they will not change with age.
Heavy vs Light: Oils paints are actually heavier than acrylics. The same amount of paint will weigh more, and this varies with the different colors. Acylic paints by comparison are light and soft and fairly uniform in this regard throughout the range of pigments.
A variety of brushes of different shapes, fibers and degrees of stiffness, will all create different effects with oil paints. Acrylics are not easily handled with a stiff bristle brush because the paint is so light the brush will tend to plow the paint instead of deposit it in a controlled fashion. The inexpensive, soft synthetic sable brushes are more suitable for most applications with acrylics. Read on.
Working on a couple of 'tree portraits' in acrylics. I can add all kinds of texture using gel mediums to create 3D effects. These kind of thick applications can be more problematic with regards to permanence with oils.
Good Brushes vs Bad Brushes: Having as wide variety of good quality brushes with different types of fibers will allow the skilled oil painter to create a myriad of effects and textures in their paintings. And if these brushes are properly cared for they can last for many years.
No matter how careful you are in cleaning and caring for your brushes when using acrylics, the paint will soon enough destroy them; it just dries too fast. Besides, most of those fancy effects created by good brushes in oils are lost with acrylic paint as it will flatten and shrink as it dries.
Stiff vs Flexible: Oil paints dry hard and brittle compared to acrylics which remain flexible indefinitely. As a result, oils prefer a stable, rigid support like hardboard to flexible supports like canvas or paper, especially if the later are not properly prepared to ensure they are impermeable and as stiff as possible. The great advantage here is that you have more options for painting surfaces with acrylics including all types of canvas, paper, wood products, and so on.
Acrylic polymer resin is also thermoplastic which means it will become hard and stiff in cold temperatures, and soft and sticky in a warm climate. This can be a concern when storing and shipping paintings.
A close up look at some texture effects using acrylic mediums.
Solvent vs Water: One of the main reasons many painters choose acrylics over oils is because they are easy to clean up with soap and water. Also, some people have allergic reactions to solvents. Moreover, because acrylic paint dries fast, it can be much less messy to work with.
Still, you should never wash oil paint off your body using solvents. Soap and/or vegetable oil is always the best and safest option for cleaning hands and brushes.
Acid vs Alkaline: Oil paints are acidic, acrylics alkaline. The main concern for artists here is that oil paints will cause rapid corrosion of canvas or paper if these painting supports are not properly isolated using a good sizing material. Gesso is a primer (ground), not a size, and oil seeps thru gesso quite readily.
Note too that when painted over an overly porous, un-sized surface, the oil that is absorbed by it will leave the paint film dry and very prone to cracking.
Conversely, acrylics can be used on almost any surface without a problem. In fact, it more often acts to strengthen and impart flexibility to most surfaces.
Old vs New: Oil paints have been around for hundreds of years and when used appropriately the paintings created with them will endure for centuries.
Acrylics have been around since the middle of the 20th century and continue to improve in their quality and working characteristics. Scientific studies and accelerated aging tests confirm that acrylics will likely outlast oils in almost every category associated with ‘permanent’ painting.
A classic oil painting done in two sittings using only 4 colors.
Varnish vs Varnishes: The final picture varnish for both media is the same, that is; a good acrylic solution varnish. One thin layer of this varnish is sufficient to protect a completely dried oil painting.
Since acrylics are sensitive to solvents - these varnishes are made with solvents, and solvents are used to remove them - acrylics require an additional protective layer first, an ‘isolation’ varnish. This is simply a thick layer of gloss medium, or soft gel medium (gloss) mixed 2:1 with water.
Acrylic paintings accumulate dirt faster than oils because they are porous and ‘electrostatic’; this means that the surface attracts and holds onto dust and airborne particles that readily stick to its soft, porous surface.
Acrylic paints can be cleaned with water. Never use water to clean an oil painting and do not display or store them in humid areas or places where the temperature fluctuates significantly.