I love working with square envelopes!
I used Ziller Ink in Midnight Blue and a Brause EF66 nib--my favorite. The envelopes were lined with a beautiful bright pink liner. Love. I don't know if it's the nautical-ness about the colors or what, but it's just a beautiful combination to me...and not just in weddings!
Found here
Found here
Found here
Found here