thermotype

from The Century Dictionary.

• noun A picture-impression, as of a slice of wood, obtained by first wetting the object with dilute acid, as sulphuric or hydrochloric, then printing it, and afterward developing the impression by heat.

from the GNU version of the Collaborative International Dictionary of English.

• noun A picture (as of a slice of wood) obtained by first wetting the object slightly with hydrochloric or dilute sulphuric acid, then taking an impression with a press, and next strongly heating this impression.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An image (as for example of a slice of wood) obtained by first wetting the object slightly with an acid, then taking an impression with a press, and next strongly heating this impression.