The plain base is made from a file named plain.mf and, commonly, from some other file, often called local.mf or modes.mf.
The local/modes file lists printers (and monitors), giving each output device a font-making mode, containing a description of some refinements that must be made in order to produce good-looking output. For instance, how to make the characters just dark enough, and how to make diagonal lines come out sharply.
If you want to make a base, you need a variant of the program
called `inimf'. (See The book, p 279.) For example,
plain.base can be made in UNIX by typing:
inimf 'plain; input local; dump'If using the emTEX version of for a PC, type:
mf/i plain; input local; dump