Think of Intaglio as a family of printmaking techniques. Engraving, Etching, Drypoint, Mezzotint, and Aquatint are all members of the Intaglio family because they all print from ink held below the surface of the plate.
Step 1: Define Aquatint. Aquatint is a specific method used to create tonal areas in a print. It involves dusting a plate with rosin powder and heating it, creating a porous ground that allows acid to bite the plate in a finely pitted texture.
Step 2: Categorize the technique. Because the ink is held in the pitted areas below the surface of the plate, Aquatint is fundamentally an Intaglio process. It is often used in combination with other intaglio techniques like etching and drypoint to add tone to a line-based image. While Drypoint and Mezzotint are also intaglio methods, Aquatint is a technique that falls under the broad category of Intaglio.