If I'm not mistaken, royals were primarily visual art prints made from engravings; "copper royals" for copper engravings, which were finer, and "wood royals" for prints made from woodcuts. In the 1764 Catalogue from printers Dicey and Marshall, the copper royals are among the most expensive items. Like broadsides, these were usually sold one sheet at a time; but they were sometimes printed in series; D & M featured a series of the four evangelists, each on his own sheet.