Here's another entry from Dick Johnson's Encyclopedia of Coin and Medal Terminology.
A medallic patina applied by placing the item completely submerged in a liquid bath. Immersion time is critical, often the longer the item is left in the liquid the deeper or darker will be the color. Immersion finishes are the most common of all patina finishes.
To prepare a medal for an immersion finish – as with most finishes – is to do a very light abrasive blasting, pelting the surface with glass beads or very fine sand. This creates micro size indentations, called craters or cups that accepts the liquid and holds it in the indentations. After exposure to the liquid for a proper time (ranging from a few seconds to several days) the liquid must be washed off to stop the action. Sometimes the medallic item is relieved or highlighted, then almost always lacquered. See patina, finish and finishing.
To read the complete entry on the Newman Numismatic Portal, see:
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