From for- + harden. Compare forhard.
forharden (third-person singular simple present forhardens, present participle forhardening, simple past and past participle forhardened)
- (transitive) To make hard; harden up.
1572, Golding, Calvin:
- They become forhardened, and shaking of the fears of God, do therewithal cast away the hope of salvation.
2004, M. Kevin Johnson, c-22 to B&W - Photo.net Film and Processing Forum:
- With the old C-22 chemicals you had to "forharden" the film in order to not have the emulsion come off durring processing.