Final answer:
Opaque watercolor, also known as gouache, is distinguished by its addition of chalk dust, resulting in an opaque, strong colored paint that is different from transparent watercolor and other painting mediums like oil and acrylic.
Step-by-step explanation:
The use of chalk dust in opaque watercolor, known as gouache, differentiates it from transparent watercolor. The larger particles, higher pigment-to-water ratio, and the presence of inert white pigment like chalk contribute to gouache's ability to deliver strong colors.
Unlike transparent watercolor, the underlying paper does not play a role in reflecting light through the paint; instead, gouache reflects light off the surface of the paint itself.
Large areas of color can be covered effectively with gouache, as seen in the works of Jacob Lawrence, but it is less suited for impasto techniques and fine details. Acrylic paints, on the other hand, are water-soluble but become water-resistant when dry, and are known for their durability and fast drying times.
When comparing painting mediums, it is worth noting that oil paints can be built up in thick layers called impasto but can develop cracks over time.
Oil paints also allow for a prolonged blending time due to their slow drying properties. Other mediums, such as tempera, also have their distinct characteristics, but gouache remains unique in its composition and application due to the addition of chalk, lending to its opaque quality.