Identify a technique commonly used in watercolor painting.

Wet-on-wet is a common technique in watercolor painting where wet paint is applied to a wet surface or to wet paint that is already on the paper. This method allows for the colors to blend and flow together beautifully, creating soft edges and a sense of fluidity in the piece. The water keeps the paint workable longer, enabling artists to achieve a smooth transition between colors and a luminous effect that is characteristic of watercolor art.

In contrast, techniques like dry brush, although relevant to watercolor, involve applying paint with a dry brush on dry paper, which gives a different texture and appearance. Spray paint and etching are primarily associated with different mediums altogether, such as aerosol art or printmaking, and do not pertain to the distinctive methods used within watercolor painting.