From the Contact page:

Hello APHA! I’m doing research on picture postcards from the early decades of the twentieth century, and I’m interested in determining when commercial printers in North America began to adopt petroleum-based or -derived inks. Any insight you can offer about the history of the use of inks incorporating petroleum or its byproducts—or for that matter any sources I might consult to learn more on this subject—will be most appreciated!

Many thanks, Mark Simpson, English and Film Studies, University of Alberta