dorinda said:"Historical slash! Anything at all about it--the challenges of writing slash in a historical time period, the things that have drawn you to it, the best and worst (or your favorite/least favorite) things about it or about the planning/writing process, how you like to go about it, etc."
The past is a different country and writing about it without doing research is going to produce lousy results. Ill-considered details can throw me right out of a story. For example, an Avengers fic had someone recognize that Steve Rogers is experiences technology culture shock, saying, "you've gone from transistor radios to the Internet" -- and I wanted to yell that no, Steve Rogers never had a transistor radio! Those were an amazing development of the 1960s that liberated radios from the big, delicate, power-hungry vacuum tube radios that Steve Rogers knew in the '30s and '40s. And technical details are the easy part -- when the author wants to get into attitudes and slang and subcultures (and really, everyone but The Man is in some subculture or other), it all gets harder to get right, and easier to get terribly wrong.
(I have had occasional to explain to a young writer that no, actually, in many cities in the early 1970s, finding one night stands was easier and less... scripted? fraught? than they are today. There really was a belief that The Pill made sex consequence-free and that there would never be a reason to confine sex to marriage again. Then came the neo-Puritan backlash of the 80s, 90s, and 2000s, plus AIDs... but that's a rant for another time. I wish I could have handed her Maupin's "Tales of the City".)
Good historical fic shows off the differences inherent to the times and places without turning the story into a documentary. People who enjoy reading history and then re-purposing what they've learned for fic tend to do pretty well. For example: Flamingo wrote Starsky&Hutch stories about the gay rights movement in the 1970s. Sylvia Volk wrote some Highlander stories set in the ancient world. Parhelion's Nero Wolfe stories are notable for their sense of time and place.
I'm not that good at it. I do fall into historical research sometimes -- and wow, I know a *lot* about the Klondike Gold Rush because I wanted to know more about the history of the RCMP because I fell into due South fandom. Also about the freight tunnels under Chicago for the same reason. And Navarone fiction got me interested in WWII in Crete, which for a while had me thinking about going to grad school just so I could spend time delving into the lives of British spies on the island at that time, with some professional academic guidance. Fiscal realities prevailed, so I'm still fumbling my way around historical research. I've written many things that I won't show off in public because they're just embarrassingly naive about the setting. Some of those details I knew were wrong when I wrote them, but I didn't know how to get them right, and just steamrolled on in an effort to finish a rough draft.
Another thing that draws me to historical slash is a unrealistic, exploitative romanticism. You've heard that saying about "an adventure is just someone on the other side of the world having a hard time"? I like my stories thrilling rather than realistic, which means I want to be able to ignore the squalor (unless it contributes to the story) and focus on the story of people rising above the average, doing heroic feats, finding love in a place far enough from my current world to have a gloss of romance or even exoticism. With slash, there's also the lure that it is sometimes subversive or at least bohemian, which can also be romantic or exotic. The trend can descend into... I guess id-fic is the politest term.
If I'm writing id-fic, I want to know it, and make that clear to everyone reading it. The danger is that people really do "learn" history from entertainment like "Inglorious Bastards" and get their ideas of what a romantic relationship should look like from "Twilight". And that's not okay.