Singular / plural form of the noun ‘type’ (meaning printed letters or typeface) – what are the rules?

When is the noun type (meaning typeface or text set in type) used in singular form and when is it used in plural form?

Is it referred to as a singulare tantum?

In which case is it an uncountable noun and in which case is it countable?

For example which one is correct and why?

Serif type is based on the formal principles of letterforms of the fifteenth century.

Serif types are based on the formal principles of letterforms of the fifteenth century.

Thanks