What caused this with a tipped in photo in a book

[slackercruster]

Does the photo contain acid?

It is from 1940.

 

[Ink stained Fingers]

Does the photo contain acid?

No, that's not acid, some ingredient of the offset ink did not dry off quick enough or was not colorless as it migrated slowly into the next page. Such inks were and are oil based

https://www.prepressure.com/printing/processes/offset-ink
https://www.dod.uni-wuppertal.de/fileadmin/_migrated/content_uploads/Offset_Printing_Inks.pdf