Many artists like the idea of painting with 'something to say'; i.e. with a message. I try to, but I don't feel it's obligatory. All the same, your statements will be more effective, and physically longer lasting if you take care over choosing a support for the painting.
So, what to paint on?
The decisions might seem obvious. Use watercolour paper for watercolour, and stretched canvas for oils. Seems simple enough, but then stretched canvas hasn’t been around forever. There was a time when artists mostly painted on wooden panels, poplar being considered as the best choice; which of course, it still is, if you wish to paint on wood.
For watercolour, it’s hard to beat a good quality, heavyweight watercolour paper. The surface texture will depend on your choice and what effects you seek.
For oil and acrylics, modern developments offer many alternatives. Some choices are inferior others not. Maybe a stretched canvas is superior to a canvas covered board, but not necessarily so. Much depends on the quality of the canvas, and the quality of the board. For instance, best quality linen, properly prepared, would be a better choice if it was glued to an acid-free board with a neutral adhesive. You then have the benefits of the linen coupled with the longevity of the board. There isn’t going to be any need for re-stretching later, and the board is less susceptible to damage. Certainly it isn’t going to suffer any ‘three-corner’ tears, from accidental knocks. On the minus side, in large sizes, most boards can be heavy.
There is another aspect. A canvas covered board is opaque. It won’t allow light to pass through. Hold up a stretched canvas against a strong light and look through from the back. You will see a dulled image in reverse, meaning that some light is getting through. With a board, all the light hitting the picture is reflected back at the viewer, resulting in a brighter image. If you wonder about this, put a painted canvas board and a painted canvas side by side in good light and you will see the difference. That still doesn’t alter the fact that to most people, an oil painting should be done on a stretched canvas, and most professional artists use canvases for their commercial work. I can’t argue with that.
What about painting with oils on other surfaces? I already mentioned wood, but it is possible to use oils on a good quality watercolour paper. In this case I mount the paper to MDF, or even stout cardboard, and then give the paper at least three coats of acrylic gesso. The paper won’t be harmed by the gesso, and the oil paint won’t get through to rot the paper. The resulting paintings, on a nice ‘toothy’ paper like Arches have a pleasing finish, although I wouldn’t use this method for major work. I also use MDF that has been primed with acrylic gesso, but usually only for preparatory sketches.
For acrylics the above methods make an ideal support. With acrylics, being what they are, there is no need to worry about them affecting good quality watercolour papers. So in this case you can dispense with the priming. This enables you to use the acrylics as you would use watercolour. Excellent for skies and misty background effects. The details can then be added, using the acrylic as a form of Gouache. This way you can achieve the oil-painted ‘look’, but without the unnecessary expense of canvases and boards, or the smell of turpentine!
Again though the finished painting can always be mounted to a board. As long as it is an acid-free board it won’t affect the picture. If you do mount the picture on a relatively thin board, (Mount-board is good for this) there’s no reason why the picture shouldn’t be framed behind glass. However, remember it’s in acrylic. Stuck to a board, it can also be varnished with acrylic varnish and framed in the same way you would frame an oil painting.
So, whether you consider canvas or board, let your preference and the purpose of the painting be the judge. If you are making preparatory paintings, why waste canvas? If you sell your work or paint commissions then discuss it with clients. For speculative sales and exhibitions, just be honest and state clearly what support you used. If someone really wants the painting and you have ‘played fair’ they will usually buy it, regardless of the support. I have sold preparatory oil sketches, because someone liked the effect. As we say, there is never any accounting for taste.
The final choice is down to the individual. I don’t claim to be an expert, but I have set out a few alternatives I play around with. Go ahead and experiment yourself. It’s fun. I know. I do this all the time.