How many letters does the top answer for “the act or process of making black. johnson.” have?

The most common answer is nigrification (13 letters).

Crossword clue: the act or process of making black. johnson.

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

nigrification 13 letters web-def

The act or process of making black. [R.] Johnson.

the act or process of making red. 50% similar → rubefaction

the act or process of making white. 50% similar → albification

the act or the process of making electrotypes. 50% similar → electrotyping