Q: How do I tell if a painting has been done in oil or acrylic?
For the most part, an acrylic painting will dry leaving a flat finish
and an oil painting will dry leaving signs of brushstrokes. On the
other hand, there are many mediums that can be added to acrylic paint
to simulate the appearance of oil, which makes it more difficult to
distinguish between the two.
Acrylic paint is also relatively new to the world of painting. It was
introduced about 60 years ago by artists such as Motherwell, Rothko,
and Lichtenstein. If your painting is older than this, it was probably
done in oil.
--by Camille LaPointe-Lyons