US 1158 On Japan Cover

The Japanese on the bottom-left reads "Crown Prince Visit to US Commemoration"
It is a first day issue of Scott 1158, and not the Royal Wedding pair which were issued in 1959.
The Japanese cover is off by one day in the top-left corner.
I'm curious if there's many other examples of the US Postal Service collaborating with another country's postal service to make something like this. It's always neat to see a US postmark on foreign material.

I'm also wondering what type of paper the envelope is made from. It's quite thick, and has what appears to be glitter mixed in with the pulp. Very noticeable when moved under a light.
Thank you as always.

The USA has done joint stamp issues many time. The largest which immediately comes to mind is the 1992 Columbian set issued as a joint issue of the USA, Italy, Portugal, and Spain; largest in number of joint stamps and countries involved.

Japan is know for some wonderful papers but the envelope you show was likely made by a cachet maker and not the postal agency.

Now to your cover:

This is not a joint issue. The USA stamp was honoring the US/Japan treaty ratified in 1860. However, the treaty interested some Japanese philatelist likely due to the travel by Crown Price and wife and your cover was born.

The combination of related or even unrelated stamps on combination FDCs is quite common. Google or search on eBay Hideaki Nakano.

Here, as noted, the added Japanese stamps were issued in 1959, April 10th. As to the 27th date, mistakes happen or dates are changed.

Thank you PPG!
Nakano certainly has made quite a few. I'm curious as to how he can get two countries' postmark on the same envelope... Can you request something like that so easily from the Post Office?

Belgium + France + Switzerland