I am sorry to be slow to reply to your question, but I went down a lot of rabbit holes in the process of trying to find information about swanskin.
First I must admit I was
very skeptical that "swanskin" was actually made from swans. Did you find something that indicates it was?
Next, most of what I began to find about it (in newspaper databases in which I found over 5,000 references) seems to confirm my initial skepticism.
I found references to swanskin back to at least the early 1800's (an 1874 article referred to swanskin as an "old-fashioned fabric") and most of those early references were from English or Scottish newspapers. I mention that because I found countless later references to "swanskin flannel" and I immediately suspected there was a connection with the English and Scottish wool industry. That assumption was confirmed for me when I found
1) an 1835 ad titled "
Merino (
as in merino wool) Shirts and Drawers" and which listed under that header "
One bale of swanskin flannel"
2) an 1840 ad for "
Low Woolens" and which listed under that header "
25 bales of white swan-skins"
3) an 1862 English ad for "
Woolen Swanskin"
4) a 1948 article stated: "
Swanskin is a soft, thick woolen cloth; or a kind of flannel"
I also found later references to swanskin silk and while there was never a definitive explanation about that I found a 1901 article that discussed it:
and this 1895 article
and this 1959 tidbit
Finally, I found references to swanskin leather, which led me to wonder if they were *really* using the skin of a swan, but then I found this 1954 item
and a 1934 ad for shoes noted the Oxford shoes were made with "Swanskin (which) is a soft, pliable leather with an attractive grain that makes it adaptable for wear with town or country tweeds."
My reaction to all this, then, is that Swanskin is a fanciful name for a leather/silk/flannel made from calfskin/"waste silk"/cotton/wool.
Good luck with your research!