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 millennium. Although other media have been used widely and successfully, 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.

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 commercial paints for general use, particularly for the outside of buildings.

In the late nineteen-forties, Leonard Bocour and Sam Golden developed and brought to market Magna paints, in which 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 were starting 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 and their toxic organic solvents required for cleaning.

Oil paints remain rooted in alchemy to a degree; 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 use of special additive media to alter their handling and properties is popular.

Early acrylics were fast to dry, making them excellent for painting in layers, but unsuitable for techniques such as ‘wet in wet’ relying 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 simply not possible.

Over the last fifty years, formulation of acrylic paints and their media have not only resulted in products that 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, enabling this flexibility, and some offer acrylic inks far more robust and durable than traditional products.

Acrylics are also able to adhere to a wide range of grounds. Professional artists often continue using prepared stretched canvas, but acrylic sizing is necessary on that and some others to prevent discolouration from the ground, termed ‘Support-Induced Discolouration’ or SID.

There are still remaining issues in using acrylic paints, though. Many oil paintings show evidence that at some stage part of their paint layer has 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 also damage the ground.

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 definitive conclusion. It’s also telling that even the innovative Golden Artist Colours offers Williamsburg oil paints, and QOR watercolours using a synthetic replacement as its binder.