Quote Originally Posted by benbenberi View Post
Georgette Heyer is delightful to read, but really not a good research tool. A lot of the social behavior and attitudes shown in her books reflect mid-19c conventions, not the Regency period (much less the 18c). A great deal speaks even more to the 1920s than to anything actually 19c.

(There are, admittedly, libraries filled with fiction by writers who took Heyer as a template and didn't actually do original research of their own. It always shows.)

If you want to do your research out of novels, at least go back to the source. Tom Jones, Tristram Shandy, Pamela... there are tons of 18c novels to look at that will give you a better idea of that period than Heyer.
I can't say as to social behavior, etc., but she was quite adept in the use of properly historical cant/slang terminology. I've been going through this book, a dictionary of slang printed in 1725, and I've lost track of the number of entries I can't use, because they would "sound" too much like copying from a Heyer novel.

So for language that is very properly 18th century, the OP might try the above link.