Recently, I wrote about my experience with maroger–a mastic-based medium. Maroger was my standard medium for a period, although I haven’t used it in a number of years. I stopped using it because details are difficult and, because it is such a soft resin, paintings are prone to scratch or show other surface insults. My mastic-based paintings have not cracked or shown other issues sometimes reported about mastic, but the surface delicacy is reason enough to abandon it. I prefer my current copal-based medium in every way.
But I am writing this due to another recently discovered issue with mastic.
I have an old mastic-based painting that I need to repair. I haven’t used mastic mediums for 15 years, so the painting is 15-20 years old. It isn’t cracked or torn, but the surface has several obvious scratches. It’s a huge painting, 6′ x 8,’ and two of its stretcher strips snapped. This happened unbeknownst to me several years after the painting was finished. The heavy duty stretchers are from Utrecht and both snapped at joins. I will never buy another stretcher from Utrecht. Anyway, when the stretchers snapped, it stressed the painting in an unnatural way which resulted in several scratches. Because the canvas isn’t torn or punctured, and because it is very painterly and details are handled broadly, it should be easy to fix.
Not the case.
My usual routine when I take up an unfinished painting, is to lightly wipe the surface with denatured alcohol. This prevents new paint layers from beading. With my copal-based medium, I can wipe a 2-day old canvas without affecting the surface. My medium drys quickly and copal is super hard.
When I wiped the surface of this 15-year old mastic-based painting with denatured alcohol, I lifted paint off the surface! Not a lot, but even so! My mastic-based medium is still not 100% dry, even after all these years. Needless to say, even if I preferred mastic over copal for aesthetic reasons, I will never use mastic again.
After I clean and repair the painting, I will seal it with copal varnish.