You'll have to treat this as a bread crumb, lacking sources as I do, but I believe that the nadir of printing quality was in the mid 1900s, when rapidly decayi

You'll have to treat this as a bread crumb, lacking sources as I do, but I believe that the nadir of printing quality was in the mid 1900s, when rapidly decaying mass paperbacks were on the market. I think that particular strain of bad quality left the market. OTOH, I have a full set of the 1911 Encyclopedia Britannica that is entirely readable and mostly in good condition, with nothing except gentle handling, regular dusting, and infrequent treatment of the leather binding to prevent red rot (because I don't read them frequently enough to prevent the condition with oil from my skin). Edit: it wasn't hard to find a page discussing the phenomenon of acidic paperbacks: https://library.uoregon.edu/catdept/presbind/brittle https://library.uoregon.edu/catdept/presbind/brittle