The modern equivalent of this is using italics to indicate foreign words, although italics is now thought of as just "slanted letters" rather than a distinct script.
Alchemists had a large collection of symbols that they used to represent elements (and various other things). Most descriptions I've seen of this just call them "symbols" in a vague way without showing how they're actually used. The reality is they're logograms, used to represent words in text, in a way very similar to how kanji are used in Japanese:
Here <♁ij> represents antimonij, <🝭m> represents retortam, and <🝋erem> represents pulverem. (You probably don't have the fonts to render those last two, and if you do the glyphs probably aren't right.)
Now here's a German alchemical manuscript that combines both of these:
German words are written in Kurrent, while Latin words are written in roman (not sure if that's the correct name), including both unassimilated Latin phrases like <Materiam primam> and loanwords like <☿rial-> (= Mercurial-). Logograms are used for both German words (<das ☉> = das Gold) and Latin words (<☿rium 🝞atum> = mercurium sublimatum, in the image below).
There are also some words that combine all three scripts. In the second-last image in this post, the word Mercurial-Wasser is written with a logogram for Mercu-, roman for -rial-, and Kurrent for -Wasser. Similarly, at the bottom of the last image, the word sublimiren is written using a logogram for subli-, roman for -mir-, and Kurrent for -en.
I've never seen this kind of writing described before.
