Q. After completing an acrylic painting on canvas, I brushed on a coat of gloss medium (25 percent water) to seal the canvas. I then brushed on a coat of matte medium (25 percent water) for a matte finish. Even though I worked quickly and was careful not to disturb the surface, the result was vertical streaks throughout—which are quite apparent on the black background. To make matters worse, the painting was dropped, resulting in a 6-inch scratch that shines like a pencil mark. Help!
A. I think the problem here is the use of the matte medium over the gloss medium: The matte material has a tendency to look cloudy, especially when applied over a dark background. Im afraid that without extensive professional treatment by a conservator to remove the matte medium (and the scratch), this painting should be considered a learning experience.
Next time, use a matte varnish over the gloss medium. Golden Artists Colors makes a removable acrylic polymer emulsion varnish in both satin and flat finishes; it can be thinned with water for application in a ratio of three parts varnish to one part water. Theres still a chance it might appear streaky when applied over dark colors, but at least its much easier to remove if youre not satisfied with the results.
You could also try a mineral spirits-thinned acrylic solution varnish. Soluvar (Liquitex) comes in a matte version, and you might have better luck with this.