A lot of people seem to enjoy the physical description of Papa’s diary that I posted a while back, so I figure a little antique stationery porn might be in order before I start posting Papa’s letters. Let’s take a quick look at what he used for most of his letters to my grandmother in 1925:
Papa mailed many letters in 6 1/2 X 4 1/2-inch envelopes, like the one pictured above, with his return address (94 Attorney Street) pre-printed in the upper left in an all-caps, sans-serif typeface. 
It looks like my grandmother opened most of them from one side rather than from the top.
His 5 1/2 X 8 1/12-inch letter paper also has his return address in the upper left. Below it and to the right appear the words “New York” followed by a blank line for the date:
The dateline, in case it’s not clear from the picture above, is pre-printed for the 1920’s:
Both the envelope and letter paper are printed on relatively lightweight stock and are a light blue-gray color. It’s all held up pretty well over the years; the envelopes show some signs of yellowing and brittleness around the edges, but most of the letter paper still feels strong and pliable. This surprises me, especially considering that these letters have been sitting in a well-ventilated suburban attic, with regular seasonal environmental swings from hot and humid to cold and dry, for the last several years. (I’m also surprised at how well Papa’s diary has held up over the years, but perhaps I’ve just underestimated paper’s staying power.)
Papa had only lived in his apartment at 94 Attorney Street since February of 1924, so he must have had this stationery printed at some point around then. The form his correspondence took was obviously important to him — as we’ll see, he occasionally apologizes for writing on regular paper or informal stationery in some of his letters — but it looks like 1925 and some of 1926 were the only years in which he used personalized envelopes and paper.
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Update:
If you want to see Papa’s letters in their original size, click the thumbnail images on the right side of any page featuring a letter. A full-sized image of the corresponding letter will pop up in a separate window.