Final answer:
Watercolor is a transparent medium, while gouache is opaque. Watercolor dries quickly, while gouache has a longer drying time. Both can be reactivated with water.
Step-by-step explanation:
Watercolor and gouache are both water-based painting mediums, but they have some differences in opacity and drying time. Watercolor is a transparent medium, meaning that light passes through the color and is reflected by the paper underneath. On the other hand, gouache is an opaque medium, which means that it does not allow light to pass through.
In terms of drying time, watercolor dries quickly because it has a lower ratio of pigment to water. Gouache, however, has a longer drying time because it contains more pigment and an additional white pigment.
Both watercolor and gouache can be reactivated with water, allowing artists to make changes even after the paint has dried. However, watercolor is known for its sensitivity and can easily become overworked, while gouache can be used to cover large areas with color due to its opaque nature. Additionally, gouache has a matte finish, while watercolor relies on the whiteness of the paper to create highlights.