Turned from the "eau-forte Par Jacquemart" To the strait head Of Messalina:
Just in case Part One of "Hugh Selwyn Mauberley" was a little too easy for you, Pound decided to make the second part even more fragmented and hard to follow. So we start Section I of Part Two with the word "Turned," having no clue what the context is.
Our Google search tells us that the "eau-forte" refers to an etching by French artist J.F. Jacquemart. So maybe the speaker of this part of the poem has turned away from this etching for some reason to look instead at "the strait head/ Of Messalina."
Strait here means strict or narrow, and Messalina was the wife of the Roman Emperor Claudius, who had Messalina murdered in 48 C.E. Her face was on Roman coins. Judging by what Pound talked about in Part One of the poem, he might be referring to Messalina as a beautiful woman whose beauty has been preserved through time. Then again, though, he might not feel great about the fact that she's been preserved on money, which Pound isn't the biggest fan of.
"His true Penelope Was Flaubert," And his tool The engraver's.
Remember Penelope? She was the devoted wife of good ol' Odysseus, the hero of Homer's Odyssey. But in this poem, it sounds like the greatest love of Mauberley's life was Flaubert, the ultimate genius of French novel writing.
Not only was his greatest love Flaubert; his favorite tool was the engraver's tool. This goes well with the engraving theme set up by the Roman coins alluded to in the previous stanza. Here, Pound seems to suggest that Mauberley prefers engraving because it's a type of art that tend to last for a very long time. Similarly, Pound is probably suggesting that the awesomeness of Flaubert's writing is going to last for a long time too. It's all about beauty that lasts for Pound.
Colourless Pier Francesca, Pisanello lacking the skill To forge Achaia.
And Antonio Pisanello (1395-1455) was an Italian metal worker who didn't have the skill to make the kind of medallions they did in Ancient Greece, especially like the ones from the Greek region of Achaia.
In other words, Pound is laying down example of people who tried to do things as well as the Greeks a couple thousand years after the fact, and failed. This definitely throws a wrench into the idea that art progresses over time. If anything, Pound says that people have lost skill since Greek times.