Postal Convention Between The Papal States And The United States

Good morning
I introduce this topic to ask you, if any of you of the forum is to Acquaintances of Americans stamps used departing from the Pontifical State, deleted with papal grid, I know the only stamp that could be used it was 3 cents Scott 65, as all letters departing from the Pontifical State arrived at its destination in the United States, were taxed by 3 cents.
I greet and thank

If they are members of the UPU I wouldn't think there would be a tax, I'm I wrong?

Maybe you are thinking of the cover shown here:

http://www.rfrajola.com/2k16/papal.jpg

I sold this cover, ex Salzer, in a 1986 auction of the Tom Alexander collection (the whole collection is available in PDF format online). The image and description I show is from the book "Etats Pontificaux, 1852-1870" published by Monte Carlo Club in 2006, page 111. I provided the image to my friend Mario Zanaria and my advertisement that also shows the cover is on facing page.

I think this is the only known example in combination with a US stamp (which served served no purpose here).

The correct amount postage due was actually 5c and could not be prepaid in a foreign country with a US stamp. Most Papal States covers to US show this 5c due rate.

Thank you for the answer egregious Frajola, and for the image of the beautiful bag from her sold, there is one similar and attaching image belongs to the collection of Imperato Doctor, I started the discussion because I happened to see a 3-cent stamp . with papal grid, I managed to get a picture by the collector and move on the forum, greetings Simone

Simone,

I am aware of Dr Imerato's cover from Mario Zanaria (I was thinking 50 baj covers ... )

Your 3c US stamp has a barred cancel used at Columbus Ohio. It comes in greenish and black and is often called "Prison Bars" cancel. It is not uncommon.

thank you so much I thought it was a cancellation Grid, looks a lot like
Thank's very much