In typefaces, i know the best known example of ink traps is Matthew Carter’s Bell Centennial. But It was released in 1978, i believe that he wasn't the first to use ink traps. I found traces of ink traps in this article (as shown in the figure) which was published in 1957 https://issuu.com/birkhauser.ch/docs/adrian-frutiger-typefaces/10
The legend of Fig 27 reads:
and the reference is:
I am confused about Figure 27 in Sofie’s thesis. Were those two letters supposed to be from an actual scan (enlarged, of course) of a printed page? If so, the ink would have dissolved at the straight junctions to create curves, wouldn’t it? Figures 28 and 29 on that same page seemed to show pre-printed letterforms—Bell Centennial loses its ink traps and becomes almost monoline when printed*. A fair comparison should be to show the metal types (flipped, of course) in Figure 27, shouldn’t it? (Side note: I don’t think “1800 century” means what the author intended to mean.)
* At its intended size, using “crappy” printing method.
A. Lawson's Anatomy of a Typeface (1990) uses the word that way, for example.
In Merlin Bold fractions, 7 pt., 1969, the numerator “3” (solid) and the denominator “2” (dashed) both featured inktraps, too.
Bear in mind that trapping is the process by which areas of ink that abut in a layout are minutely oversized, in order for them to overlap in printing, thereby not leaving a fine-line gap of white paper showing, should registration of the separate plates not be absolutely perfect. And this was a general principle, not just for type-against-colour (when not surprinted), but colour-against-colour, and halftone-against-colour,
This trapping was implemented as part of photographic pre-press production (filmstripping), by over-exposure, which did not involve ink.
In the production of photo-typositor fonts, the purpose of the traps and ticks was to pre-empt the softening (decay) of the type shape during font production and phototypesetting. So in historical investigation, the phototype filmstrips/reels/Diatronic grid-fonts are worth a look, to check for the effect. It is not mentioned in Frank Romano’s History, however, so was perhaps a bit of an under-the-radar trade secret.
When I produced the artwork for my first published typeface, Gryphon, in 1980, for Headliners International, the traps and ticks/flicks were required. Subsequently, for Shinn Sans in 1985, Typsettra also required the treatment, so I assume it was de rigueur by the 1980s.
It isn't really needed in digital type, except to counteract the effects of ink spread and similar issues in the final application of the type.
When one adds up the number of photo reproductions that occurred from phototype font original artwork to offset printing plate, it was something like six or seven—plenty of opportunity for sharpness to wither.