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eyeburp
07-09-2001, 04:47 PM
Everyone here was so helpful for my last question re: gessoed paper so here's another:

I recently experimented on a swatch of raw (unprimed) canvas with acrylic paint. Does anyone know of any archival problems with this? Should I seal the back when I finish painting on the front? Are there ANY potential problems with this that anyone could think of (cracking, etc.)? Thanks in advance as usual.

sarkana
07-10-2001, 09:44 AM
acrylic is a non-destructive medium. it has no solvent action (its solvent is water) and will not destroy its support like oils will. you don't need to put anything on the canvas before you paint on it with acrylic.

i think most painters *do* gesso or put on a layer of acrylic paint before they paint on canvas or wood. but its not to protect the support. its so the first strokes of paint won't get absorbed into the thirsty support. the worst ramification of painting on untreated canvas is that your painting may look a little "dull" as most of the paint on the first two or three layers gets soaked up by the canvas.

StarGate
07-22-2001, 04:30 PM
Hi eyeburp
The following link might be usefull in explaing using a size (even if clear so the natural canvas can show through) on your support -
Controlling SID in Acrylic Paints
http://www.goldenpaints.com/prepsupp.htm#size
John

JeffG
07-23-2001, 10:42 AM
Not that it validates any archival issues, but I believe David Hockney did (or does) alot of work with acrylic on unprimed canvas (the swimming pool images especially). Mostly for the effect bleeding would give, almost like watercolor on wet paper.

carly
07-23-2001, 11:33 AM
The acrylic paints would seal the unprimed canvas and soak into the fabric. Although canvas is highly durable, you could have damage to the back side if left unsealed. Discoloring would be the first evidence because dirt and oil would collect on the fibers. Personally I would paint over the back side with at least one coat of gesso or other sealer.
carly

cuttlefish
07-23-2001, 03:12 PM
Originally posted by StarGate
Hi eyeburp
The following link might be usefull in explaing using a size (even if clear so the natural canvas can show through) on your support -
Controlling SID in Acrylic Paints
http://www.goldenpaints.com/prepsupp.htm#size
John

That bit's short, but important enough to be presented here.
from Golden Artists Colors web site
Support Induced Discoloration (SID) is a phenomenon that occurs in acrylic paints and mediums. As a paint film cures, the water exits two ways: out into the atmosphere, and through the support if the support is porous enough. Canvas, linen, wood and masonite are all porous enough to allow the water to absorb into them. Additionally, during this drying process, the water is actually in equilibrium moving back and forth between acrylic paint and support. During this time, the water extracts water-soluble impurities such as dirt, sap, starches, etc., from the support and deposits them into the acrylic film. The result is a discolored, typically amber, film, with the degree of discoloration dependent on the amount of contaminants deposited. This in turn is dependent on the inherent level of such in the support, as well as the drying time of the paint. Longer drying times can be caused by higher relative humidity, lower temperatures, less air flow and thicker paint films, all of which can increase the impact of SID.

This contamination often goes undetected. In most cases, the paints applied contain a sufficient level of pigment, thus a strong enough color, to conceal the yellowing. However, in a transparent glaze and especially in thick translucent gel layers, SID becomes quite noticeable. SID can transform the appearance of an Ultramarine Blue glaze into a lower chroma, greenish color. Gesso alone will not stop SID, and different gels and mediums have varying degrees of blocking capabilities. The best product GOLDEN produces to prevent SID is GAC 100. This thin medium works best when 2 or more coats are applied directly into the support. Once dry, the canvas can then be primed and subsequently painted with less potential for discoloration.

woodciro
07-23-2001, 08:09 PM
"Personally I would paint over the back side with at least one coat of gesso or other sealer."

Carly, wouldn't this apply even if the front WERE gessoed?

John