I am having fun engraving old patent drawings on tile. Finding them is always a challenge because there are some sites that have fake drawings and of course are not public domain. Other sites have taken the originals, colorize the drawings and add extra information. So what is a maker to do?
I came across this site that has all the information and links you need to find legitimate drawings for use.
Have fun!
This site explains how to search the USPO search site.