phrases - Etymology of "typeface Weight"

My boss stated that he noticed the word "weight" is used to refer to the boldness of a character, and stated that he felt this was a new occurrence.

My gut feeling is that this is an old term, derived from the typesetting industry and made popular with the advent of personal computers, desktop and web publishing. I also suspect that the term had something to do with the physical weight of typeset letters, but this is just a supposition.

While Google's n-gram viewer shows a massive increase in "font weight" usage starting around 1985 (which corresponds to the usage spike of the term "desktop publishing"), there were smaller spikes around 1830 and 1932.

A search for the etymology of the use of weight in regards to the darkness of the typeface revealed nothing.

Does anyone know the source of this phrase?

Answer

OED has a draft addition from 1993:

Typog. (a) The heaviness of a fount of type, determined by the thickness of strokes in the individual sorts; (b) the degree of emphasis or blackness of a typeface.

1771 P. Luckombe Hist. & Art of Printing 239 A Fount of Roman Letter, of what Body or Weight soever, is constituted of Lower-case Sorts, Capitals, Double Letters, [etc.].

(along with several other later citations)

It is true that individual letterpress letters would be very slightly heavier if they printed a bolder letter [at the same size], but it's unlikely to be a substantial difference.

OED has a related entry for weight, which I suspect is at its root:

2. Associated with measure and number, esp. in figurative expressions referring to due proportion.

The earliest citation for this use (which would later be applied to type) is from c1250.