19th Century lithography is unequalled, even today. Just look at some of the theater posters in the Library of Congress collection to see how high the standards were back then.
And they made all those illustration engravings by hand. Amazing.
The other element is the paper, which was made with virgin pulp and pure cotton or linen fibers, because there was no polyester then. Recycled paper didn't become a "thing" until the 1980s.
I imagine the inks were still largely plant-based and natural, as well.