Sagging and Puckers in Stretched CanvasRemove the tacks or staples in the area of the problem (or if needed be all the way to the corner) and re-stretch the canvas. For small puckered spots, take a damp cloth and lightly wet the back of the canvas in the area of the pucker and allow it to dry. If pucker remains, the canvas should be re-stretched.
Wrinkles
Wrinkles in unprimed and primed canvas can usually be pulled out with a little extra effort when stretching. Wrinkles in unprimed canvas can be removed prior to stretching by steam ironing.
Texture of Primed Linen Canvas
Because of the nature of the fiber and the weaving process, linen yarns may vary as much as 200% in diameter in one spindle and there is no predicting how this variance will show in the fabric (random bumps, lines, etc.) Most surface irregularities are par of the lien surface construction and its character.
Edge Cracks When Stretching Primed Canvas
Primed canvases have a tendency to crack under strong stretching tension when pulled over sharp edge, especially as they age. Cracking is more pronounced with oil primed canvas than acrylic primed.
Oil Painting on Acrylic Gessoed Canvas
In most cases it is ok to apply oil paint over completely dry acrylic gessoed canvas. The texture of the canvas and the calcium carbonate in the acrylic gesso allow the oil paint to adhere and absorb into the acrylic gesso. If the acrylic gesso becomes slick it might adversely affect adhesion of the oil paint. Apply a light wash of 1 part linseed oil and I part mineral spirits over the surface. Let dry 24 hours.
Oil Painting over Acrylic Paint
In most cases it is OK to apply oil paint over completely dry acrylic paint. The adhesion is physical and not chemical. If the acrylic paint is not completely dry, the moisture trapped in the acrylic paint will adversely affect adhesion. If the acrylic paint is thick and eliminates the texture of the canvas, the surface will become slick, and adhesion will be adversely affected. To increase adhesion in the scenario, apply a light wash of 1 part linseed oil and 1 part mineral spirits over the surface. Let dry 24 hours. Note: acrylic paint should never be applied over oil paint.
Oily or Dull Oil Primed Canvas
An oily or dull primed canvas might adversely affect paint adhesion. Before painting, wipe the surface with a lint free cloth saturated with mineral spirits. If the problem persists, wipe the surface lightly with a 50/50 mix of linseed oil and mineral spirits and allow it to dry at least 24 hours.
Washes or Veils
When applying washes of oil paints to acrylic gessoed canvas, seal the canvas prior to application with mixture of 1 part linseed oil and I part mineral spirits. Apply in a very thin film with either a brush or a lint free cloth. Let linseed oil dry for 48 hours.
Rolling Canvas
Make sure paint is completely dry. Oil paint: 6 months; acrylic paint: 1-2 weeks. Roll canvas around a large diameter cylinder. Always roll painting side face out. Do not place regular paper over the painted surface. Use glassine paper: Note: acrylic paint will permanently stick to itself in hot weather.
Storing Stretched Canvas
Always store canvas in a vertical position. If stored horizontally, canvas will sag over time. Avoid leaning canvases upon each other. If canvases must lean upon each other, lay same size canvases face to face or back to back. If tored face to face, place glassine paper between canvases. If canvases are different sizes, place a sheet of cardboard between the canvases.