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The vehicle and binder of oil paints is linseed oil, whereas water serves as the vehicle for an emulsion 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"

 

The main practical difference between most acrylics and oil paints is the inherent drying time. Oils allow for more time to blend colours and apply even glazes over under paintings. 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. In 2008 Golden Artist Colours introduced a slow drying acrylic paint with working qualities similar to oils, but indistinguishable from regular acrylics when completely dry.

This new acrylic paint can remain wet and workable on a palette for several hours and even days under normal conditions.

 

The fast evaporation of water from regular acrylic paint films can be slowed with the use of acrylic retarders. Retarders are generally glycol or glycerine-based additives. The addition of a retarder slows the evaporation rate of the water, and allows for more water to be added and the paint workable, until the retarder has left the film and the paint layer is dry.

 

Oil paints 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 soluble oil paints have been developed for artist use.) Oil paint films 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 is able to absorb substantially more pigment than acrylic because linseed oil has a smaller molecule than does acrylic. Oil provides a different (less clear) refractive index than acrylic dispersions, imparting a unique "look and feel" to the resultant paint film.

 

Due to acrylic's more flexible nature and more consistent drying time between colours, 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 primed and gessoes before painting with oil, acrylic can be safely applied to raw canvas. The rapid drying of the paint tends to discourage the blending of colour and use of wet-in-wet technique unique to 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. Whereas oil paints normally turn yellow as they age/dry(oxidize)—and require a removable protective layer of varnish—acrylic paints, at least in the 50 years since their invention, have not yellowed, cracked, or altered.

 

Another difference between oil and acrylic paints is the versatility offered by acrylic paints - acrylic is very useful in mixed media, allowing use of pastel (oil & chalk), charcoal, pen, etc. on top of the dried acrylic painted surface. Mixing other bodies into the acrylic is possible - sand, rice, even pasta may be incorporated in the artwork. Mixing artist or student quality acrylic paint with household acrylic emulsions is possible, allowing the use of pre-mixed tints straight from the tube or tin, so presenting the painter with a vast colour range at his or her disposal.