Aquatint Etching Technique Explained

My Miro is an etching -- not a painting. Specifically, it is a color wash and aquatint etching, that used copper plates (one for each color) on pressed on paper. The following explanation is from Wikipedia:

An aquatint begins with a copper or zinc plate. The artist applies a ground by either dissolving powdered resin in spirits or applying the powder directly to the surface of the plate. The plate is then heated; if the plate is covered with powder, the resin melts forming a fine and even coat; if it is in spirits, the spirits evaporate and the result is essentially the same.

Now the plate is dipped in acid, producing an even and fine level of corrosion
(the "bite") sufficient to hold ink. At this point, the plate is said to carry about a 50% halftone. This means that, were the plate printed with no further biting, the paper would display a gray color more or less directly in between white (no ink) and black (full ink). At some point the artist will then etch an outline of any aspects of the drawing he wishes to establish with line; this provides the basis and guide for his later tone work. He may also have applied (at the very start, before any biting occurs) an acid-resistant "stop out" (also called an asphaltum or hard ground) if he intends to keep any areas totally white and free of ink, such as highlights.

The artist then begins immersing the plate in the acid bath, progressively stopping out (protecting from acid) any areas that have achieved the designed tonality. These tones, combined with the limited line elements, give aquatints a distinctive, watery look. Also, aquatints, like mezzotints, provide ease in creating large areas of tone without laborious cross-hatching; but aquatint plates, it is noted, are generally more durable than mezzotint plates.

The first etch should be for a short period of time (30 seconds to 1 minute, with a wide variation depending on how light the lightest tones are meant to be). A test piece may be made with etching times noted, as the strength of the etchant will vary. More than thirty minutes should produce a very dark area. Etching for many hours (up to 24) will be as dark as etching for one hour, but the deep etch would produce raised ink on the paper.