Oki ML6300FB User Manual page 42

Emphasis printing
Do not use emphasis printing if performing horizontal
tab character printing on thin paper as the paper may
become damaged.
Use this for printing multipart forms.
You have to set emphasis printing by using the menus to set
Impact Mode to Hi Copy as described in "Menu setting" on
page 33.
Notes
If the paper on top is so thick that duplication on the
paper below it fails, use emphasis printing.
In emphasis printing mode, printing is carried out
twice.
The print may become blurred if high density
characters and graphics are printed using a new
ribbon.
In emphasis mode, ensure that the paper is flat to
avoid possible printing errors.
CAUTION!
Operating instructions > 42