There are various types of paint that are generally divided into two categories – water based and oil based paints. Paints are applied with a variety of brushes, pallet knives, etc. The most common water based paints are watercolor, gouache, and acrylic. Watercolor and gouache are generally applied on paper, whereas acrylic is most often applied to canvas. These mediums are generally fast drying. Acrylic has the best durability and is generally used in much the same way as oil paints. The finished work is resistant to moisture once it dries and can be exposed to the environment when framed. Watercolor and gouache, however, must be protected from moisture because water will re-activate the paint and damage the finished work. As a result, finished works must be framed, matted, and placed under glass. Oil based paints are most often applied to canvas or wood panels. Oils are long lasting and slow to dry. The finished artworks are resistant to moisture.