Nina asked: Hmm… so what are 'Sentence Capitals'? :) Here
Perhaps I can elucidate...
BTW Forgive me if I am going over old ground - but would be interested if anyone else has investigated this (intentionally).
When looking at set type, I quite often find, that the capital letter that starts the sentence in relation to the rest of a word is bold in appearance. Because I am not convinced this is necessary for set text I am investigating the idea of specially optically-balancing the capital letters to the weight of the following lowercase glyphs.
There is a precedent in having bolder capitals. This is clearly seen in Scotch Roman. Also - there might be (a remote chance) that there is some element of legacy suggesting this 'style' where capitals from an existing face were used with a slightly lighter lowercase set?
I am aware that due to the nature of a capital letter having both a less complicated structure (they are more open due to their relative size to l/c) and elongated stroke-lengths naturally lightens its form which needs to be compensated. I would still expect Capital strokes to be thicker than lowercase however to a lesser degree than what is currently considered 'normal'
Capitals tend to be designed with other capitals so the design ecosystem is not the same as real world use. i.e. I suggest that more consideration is given to how the capital 'exists' with the lowercase rather than its CAPITAL glyph relatives.
However - What seems to happen is that these lighter capitals that have been designed to work as an initial capital in a word don't look so good when set ALL CAPS.
So what we see in fonts for the most part (but not Scotch Roman) is that a compromise has been allowed for so that the caps looks great when set ALL caps and OK when set with lowercase.
My thinking is that this balance can be readdressed so that the Capital letter designed to compliment with lowercase gets the priority styling consideration and that if necessary a secondary set of capitals for ALL CAPS can be supplied.
I hope soon to supply some 'proof of concept' but would welcome points of view and other examples by those who care to give this some consideration...