Spray painting, a non-traditional art form, is a good way to create spiffy, contemporary images based on graffiti motifs, abstract patterns or your own designs. You won't necessarily create an archival work that will last decades, but for a craft project, sign or other similar use, spray paint on canvas is suitable and efficient.
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If you have a piece of raw, unprimed canvas, you can paint directly on it. On the upside, it couldn't be easier. On the downside, the spray paint can degrade the threads more quickly than if the canvas were primed. Also, the spray paint can soak in more quickly, and is thus susceptible to slight bleeding. You may like that effect, however, as it produces softer color and edges.
Linen is a high quality surface, suitable for fine art projects. It is darker, and should be primed so the colors show better. Use an acrylic gesso primer. Linen can have a much finer weave than other canvases. Portrait linen is among the finest, and great for uses where you do not want texture. If you are on a budget, though, try a different canvas type.
Jute and Textured Canvas
Jute and other more heavily textured canvases are more economical than linen. Many share the deeper tone, and should thus be primed. If you want a cheap primer you can use white house paint, though this is far from permanent. The texture in these weaves can be quite noticeable, and you will have to consider if you desire this quality as part of your project.
Synthetic canvas is a quick and easy choice. It is less expensive than professional canvases, and often is pre-primed, or not in need of primer. Some synthetic and cotton blends are also available. In addition to these advantages, some synthetic surfaces can be purchased with grommets already embedded in a pre-cut piece of canvas, which makes it a good choice for signage.