What is the X in X-mas?
by 1909, shortening of decalcomania, from French décalcomanie, from décalquer (18c.) "transferring of a tracing from specially prepared paper to glass, porcelain, etc." (in vogue in France 1840s, England 1862-64), from de- "off" + calquer "to press," from Italian calcare, from Latin calcare "to tread on, press."
Time was when there were only printers employed in making the sheets that were stuck on the ware, giving the old-time term of "plain print." This form of decoration was succeeded a few years ago by the decalcomania or "decal." This "decal" is an imported sheet, lithographed, and the little sprigs, flowers and scenes are cut out and stuck on the ware. ["Brick, the Leading Clay Journal," April 1909]
design that is printed on specially prepared paper to form a film that can be transferred to any surface. Such films are widely used for decorating and labeling any objects that cannot be run through a press