I had posted a request for help in identifying a coat of arms a couple of days ago (http://blog.appletonstudios.com/2013/03/a-request-for-assistance.html). I'd also requested help on a couple of heraldry society forums to which I belong. I am happy to be able to report that a correspondent has been able to identify the arms! Her email noted as follows:
This one is from the Insignia ... V. Insignia urbium Italiae septentrionalis: Nobilium Mediolanensium - BSB Cod.icon. 270, one a set of fifteen 16th Century Italian armorials which have been digitized and uploaded to the website of the Bavarian State Library in Munich.
This image is from Wikimedia Commons.
As you can see, these arms match those on the jar in question.
The arms are those of the Gritti family of Venice, one of whose members, Andrea, was Doge of Venice from 1523 to 1538. (More information about Andrea Gritti, as well as a portrait of him painted by Titian, can be found at http://en.wikipedia.org/wiki/Andrea_Gritti) Given that the jar was made around 1500, it is entirely possible that it was made for Andrea Gritti while he was Doge.
I did find myself a bit annoyed at myself, since I had looked through my copy of the Stemmario Trivulziano which has yet another depiction of these arms, but I hadn't caught it. My only excuse is that when thumbing through some 250 pages of heraldry at nine coats of arms to a page (not yet knowing a name to look up in the index), I somehow missed it. Still, it was right there. Well, thank goodness I have friends to help make up for my shortcomings.
Thank you all who spent some time looking for this coat of arms. And thank you Anne, for finding not one, but three, depictions of this coat of arms. I appreciate the help. Truly, I do.