Canvas is the traditional, and most commonly used, surface or substrate for Oil and Acrylic Painting. Ready-made Canvases are made from woven linen or cotton which is then either stretched over wooden stretcher bars or adhered to a suitable board.
Why is canvas primed? The stretched canvas or board is basically the support for the layers of paint. For the Oil or Acrylic Paint to bond with the surface and withstand environmental and chemical changes over time, the support is usually primed with Gesso - with the gesso becoming the actual painting surface. Gesso is predominantly white but some colours and clear gessos are available. There is also a trend to paint directly onto unprimed, natural canvas which can give some great effects but is should be noted that the paint - especially Oil - will sink into the support without the barrier of the primer and result in more subtle, muted colours.
Can any wood be used as Stretcher Bars? Good quality Stretcher bars are of a solid, mitred construction and generally kiln-dried so that they do not warp. Pine is the common option with the bars laminated to, again, reduce the risk of warping.
How taut should a Stretched Canvas be? This will depend on what you prefer to work on. To accommodate most preferences, ready-made canvases are quite often produced with some slack in them and come with wooden 'wedges' that you can hammer into the corners to pull the Stretcher Bars apart and, therefore, increase the tension on the canvas material.
What glue is advised for making Canvas Boards? The best glue for making your own bespoke canvas boards from canvas sheets and a suitable board such as greyboard is Rabbit Skin Glue which comes in pellets that be melted down as required or ready-made in a gel-like form.