Recently, I have been watching "princess" movies such as Belle or A Royal Affair, and I think this picture is representative of what I am thinking of. Note the cleavage -- some shows (e.g. Penny Dreadful) show dresses that have even more.
Was it really common for people of that era to reveal that much? Or are these modern tastes discretely inserted into period television? Am I wrong in my impression that in 19th century America and England at least, it would not have been considered proper for someone to dress like that?
Yes, they are the modern tastes- showing realistic XVIII century cleavage would earn it PG-13 if not higher rating. http://upload.wikimedia.org/wikipedia/commons/0/0b/Charlotte_Esther_Denner_1761.jpg
http://en.wikipedia.org/wiki/File:Mrs_Benjamin_Pickman_by_John_Singleton_Copley.jpeg
Fashion plates were a grandmother of modern fashion magazines. IMHO above could easy qualify as "bare breasts" to modern people.
For XIX century- the fashion changed from Rome-inspired dresses of Napoleonic age, middle of the century hoop-skirts, rich Victorian dresses to slender Gibson Girl. I'm not familiar with Penny Dreadful, but XIX century bon ton paid a lot attention to the time and place- remember Mammy reminding Scarlett that Evening dress is improper for barbecue? Here are dresses suitable for meeting in daylight http://en.wikipedia.org/wiki/1860s_in_Western_fashion#mediaviewer/File:1862-vienna-fashions.jpg
And evening one http://en.wikipedia.org/wiki/File:Magnus_Jenny_Lind.jpg
