Studio Craft: Troubleshooting Retouch Varnish

Ask the Expert: "I've been having issues using my favorite brand of retouch varnish. I applied 3 light coats to a touch dry painting and there are irregular patches of gloss and matte appearing after the varnish is applied. I use stand oil and turpentine for medium. There are also yellow splotches appearing on the back of the canvas as well, but the splotches don’t seem to match up with the splotches of matte and gloss on the front of the canvas. I’m guessing that if I wait to apply a final varnish, it will even out the glossiness ?"

A: Retouch won't generally perform as well as a heavier, final top coat in terms of overall sheen. Some dull spots are to be expected, especially where paint is very fat. It's still worth using retouch, though, because it does keep dust and contaminants from coming in direct contact with the paint surface, and while it isn't perfect, the overall appearance of a fresh canvas with retouch is a lot more presentable than just bare paint.

Since stand oil is the medium, fat passages are probably present, and that's probably where the dull spots manifest. It's OK to add more retouch varnish as needed where this occurs. We recommend resisting the temptation to use a heavier varnish too soon, however, because although (contrary to what some believe) varnish won't "suffocate" paint and prevent drying, dimensional and chemical changes in the paint can spoil a varnish layer, causing orange peel texture, hazing and other defects. It's a lot easier to remove or re-wet retouch than it is to remove a heavy, final top coat.

If your favorite product doesn't yield desired results, there are other brands that will work, including some ketone-based products that work as retouch in a light coat, and which can also be used as a final coat.

The yellow spots on the back of the canvas are probably just the medium striking through the primer to the fabric support, unrelated to the varnish.

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