When using shaped frames, we recommend that unprimed cotton or linen canvas be stretched first and then primed. The unprimed canvas is more flexible and can be pulled tight around curved edges without creating folds in the canvas. The photo above shows a round canvas stretched on a 60” diameter frame. The visible edge is free of any folds but the folds are quite pronounced on the back side of the frame. The thicker the frame, the more difficult it is to avoid folds in the canvas along the edges. For this reason, we try to keep most frames under 1-1/2” in thickness.