Cotton duck canvas is much less expensive than linen & has become the most popular support for oil & acrylic painting. A properly prepared cotton canvas has longevity similar to linen, and is more flexible & easier to stretch properly. However, cotton is considered too flexible for very large paintings & therfore linen is sometimes preferred. Cotton can be used For both oil & acrylic painting.

Cotton duck is made from the threads of the cotton plant which are spun into larger fibres, offering moderate strength.These fibres are then woven into a heavy canvas which is rated on a numerical grade system of thickness from 1 to 10, 1 being the heaviest & 10 being the lightest. Cotton is readily available & relatively inexpensive, making this canvas type the most popular for artists to use.

Linen canvas with an oil primer is the classical standard for oil paintings. An acrylic primer, less expensive than oil primer, can be used with either acrylic or oil paints. Linen is difficult to prime & stretch properly, but it offers the smoothest & stiffest painting surface, one with proven longevity.

It is made from long extremely strong fibre strands originating from the flax plant. Linen is an expensive fabric to manufacture. The quality of the finished linen depends largely on the quality of the plant itself.

Good quality linen is soft & largely free of the slubs or small knots often associated with it. Slubs are only found in lesser quality fabric. Linen is moth resistant & repels dirt, as well.

Stretched canvas means that the canvas you are purchasing is already stretched over a frame of stretcher bars to a predetermined size. Stretched canvas is almost always primed with some kind of gesso so that if you are in a big hurry they are ready to paint on from the time you remove the plastic.

If you are an artists who is a little more particular about the size or the finish of your canvas then you may choose to stretch your own canvases. If so, you will need to purchase stretcher bars and assemble them into a stretcher frame. Then you basically need to upholster the frame with the canvas, make sure to get all the wrinkles out get the tension even across the whole canvas. You will need to purchase a staple gun and a pair of canvas pliers. You can choose to purchase rolls of canvas that are either primed or raw. Some artists like to prime their own canvas to customize the painting surface to suit their particular painting style. Side stapling is the least expensive technique for securing the canvas to the stretcher bar, because it uses less canvas. Finished pieces can also be framed to hide the staples.

Back stapling is a more expensive finishing technique, and it requires more canvas, but it provides more salvage for restretching. Some artists paint on the side as well as the face, creating works that don''t require framing.

Spline finishing is the most expensive finishing technique, and some artists feel that it is not as easy to restretch the canvas as with back stapling.

Loose canvas can be a big concern for artists and manufacturers of Stretched Canvas. Certain environmental conditions will cause a canvas to either slacken or even tighten. In dry climates, as in mountainous states in the winter, for example, canvases are susceptible to slackening. Moisture causes cotton and linen canvas to temporarily shrink, but when the moisture in the air dries up, the canvas will slacken. This is an unavoidable fact of nature.

The primary concern is when a painting is hanging on a wall, it shows sags, and possibly ripples, when it is slackened. This is the reason Stretcher Bars were invented 150 years ago to provide a fix for artists to adequately display their art. Keys or wedges are inserted into the inside perimeter of the frame corners to expand the size of the canvas, thereby restoring the flat canvas during display. The problem with Stretcher Bars is that when a canvas is displayed in a frame, it may make it impossible to adequately enlarge the canvas frame inside the picture frame, and provide the tension it needs to display flat.

Numbered ducks identify canvas that uses at least a 2 ply system on the warp and filling and whose weight is identified by a system of numbers. For instance per square yard, #12 is about 11.5 oz.; #10 is about 14.5 oz.; #8 is about 17.55 oz, and so on. These are the most common medium-heavy weight canvases that you will see for sale.