The Collaborative International Dictionary
Thermotype
Thermotype \Ther"mo*type\, n. [Thermo- + -type.] 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.
Wiktionary
thermotype
n. 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.