Traditional oil paints were the mainstay medium used by professional painters in the west from the Renaissance until the late twentieth century, a period of well over half a millenium. Although other media have been widely and successfully used, until recently the apparently infinite flexibility of effects and painting styles made oil paint dominant. Over that period, much effort has been expended getting oil paint to dry more quickly, and discovering how to create stable paint layers using principles such as the ‘fat over lean’ rule.
Then in the nineteen-thirties, Otto Röhm invented a new synthetic resin formed from acrylate molecules, dubbed acrylic resin. This first became available dispersed in liquid during that decade, and was steadily developed into paints during the nineteen-forties. Their biggest market was in general-use commercial paints, particularly for external use on buildings.
In the late nineteen-forties, Leonard Bocour and Sam Golden developed and brought to market Magna paints, in which the acrylates were suspended in mineral spirits to form an emulsion. Golden later developed a paint based on water, which lives on in his company Golden Artist Colours. In the nineteen-fifties, they were joined by Liquitex, then in the sixties by Rowney’s Cryla paints. Acrylic paints started to rival oils.
In modern acrylic paints, the acrylics themselves are the binder, with water as its diluent. Wet paint is readily removed from brushes and skin using soapy water, making the use of organic solvents largely unnecessary except when dealing with dried paint. This is much more convenient than working with oils, with their toxic organic solvents for cleaning.
Oil paints are still to a degree rooted in alchemy; although modern commercially-made oil paints are sophisticated combinations of natural and synthetic ingredients, using them and controlling their visual effects owes as much to tradition as it does to industrial chemistry. Acrylics are thoroughly modern in their formulation and use, carefully packaged blends of polymers with surfactants, plasticisers, dispersants, defoamers, stabilisers, and of course pigments.
Some artists still grind their own oil colours, and many oil painters use traditional media and resins to control their properties. Acrylics are too chemically complex for artists to prepare themselves, although the use of special media to alter their handling and properties is popular.
Early acrylics were fast to dry, making them excellent for painting in layers, but quite unsuitable for techniques such as ‘wet in wet’ which rely on the interaction of wet paint on the ground. Hard edges were easily achieved, as were bright if not garish colours, but effects such as sfumato were impossible.
Over the last fifty years, formulation of acrylic paints and their media have not only resulted in products which remain ‘open’ for longer, but have let painters determine body, flow, finish, and other physical properties of acrylic paint. Paint manufacturers even have fine control over the size of acrylic particles within the paint emulsion, which enables this flexibility, and some offer acrylic inks which are far more durable and robust that traditional inks.
Acrylics are also able to adhere to a wide range of grounds. Professional artists often continue to use prepared stretched canvas, but acrylic sizing is necessary on that and some other grounds to prevent discoloration from the ground – ‘Support-Induced Discoloration’ or SID.
There are still remaining issues in using acrylic paints, though. Many oil paintings show evidence that at some stage part of the paint layers have been scraped off to enable the artist to repaint sections in pentimenti; this isn’t normally possible with acrylics, which tend to be overpainted without scraping, as the latter strips the entire paint layer and may damage the ground too.
Experience from accelerated ageing of acrylic paints suggests that today’s acrylic paintings should last better than oils. However, the oldest acrylic paints are still well under a hundred years old, making it far too soon to arrive at any robust conclusion.