IIRC, you can either recreate the ink from a recipe, find old ink and re-dissolve it, or if you have the patience you can extract it from old pages.

“Hofmann also learned how to manufacture inks using the same components and methods used by contemporary artisans.”

https://www.ioba.org/standard/2002/11/genuine-fakes-mark-hof...

Is this why he collected first edition books? I didn’t realise it but this would make a lot of sense.