When was the use of \mathbb popularized as an alternative to \mathbf?
Of course there are the subjective preferences of certain authors, but when I read older articles, there appears to be an almost unanimous usage of what we would think of as \mathbf (possibly because of the use of typewriters before LaTeX), and now more recently it seems as if the use of \mathbb is becoming increasingly common.
Is there a reason for this switch in notation?