Watercolor is a painting method in which the paints are made of pigments
suspended in a water-based solution. Watercolor refers to both the
medium and the resulting artwork. Aquarelles painted with water-soluble
colored ink instead of modern water colors are called aquarellum
atramento (Latin for "aquarelle made with ink") by experts. However,
this term has now tended to pass out of use.
The conventional and most common support—material to which the paint is
applied—for watercolor paintings is watercolor paper. Other supports or
substrates include stone, ivory, silk, reed, papyrus, bark papers,
plastics, vellum, leather, fabric, wood, and watercolor canvas (coated
with a gesso that is specially formulated for use with watercolors).
Watercolor paper is often made entirely or partially with cotton. This
gives the surface the appropriate texture and minimizes distortion when
wet. Watercolor papers are usually cold-pressed papers that provide
better texture and appearance with a weight at least 300 gsm. Under 300
gsm is commonly not recommended for anything but sketching. Transparency
is the main characteristic of watercolors. Watercolors can also be made
opaque by adding Chinese white. This is not a method to be used in true
watercolor.