The History of Ain't

Sorry if this is a dumb question, but was "ain't" ever considered respectable in formal written English? I know that the English upper crust widely used it in conversation during the 19th century. When did "ain't" become a stigma of the lower classes?
Your pal,
Barney
Deprived of art, life instantly becomes so brutalized as to be devoid of interest. Further, there is a worse thing than no art at all - namely, the saccharine travesty of art supplied by Hollywood.
Wyndham Lewis