Thermography simulates the appearance of the more-expensive engraving process. Engraving involves the cutting of copy or a design into a metal plate. The die is inked and wiped clean, leaving ink in the impressions. The paper is then laid on the die, and the press forces the paper into the cavities of the die to achieve the raised lettering effect. In the invitation albums I've looked through, there are different prices quoted for traditional and photo lettering.
Molten lead is formed into the shapes of the letters using pre-cast molds.
The letters cannot be made larger or smaller due to the limitations of the pre-cast molds. The process starts with a photographic image of the words to be printed. The image can then be reduced or enlarged. The wedding ceremony and reception are two distinctly different types of events. Because these two events are so different, traditional etiquette dictates that separate cards be used.