Presumably you have to go back a bit further for the days when even gentlemen had to bribe an attendant to see the more explicit artworks.
What puzzles me a bit is that in the completely unrestrained portrayals of activity in the brothel most, if not all, of the females are wearing a breast-band. (I think that is the right term - like a bikini top.) I have also come across this in other Roman contexts. There must be a reason for this, but what is it?
I remember reading in this book (link below) that Romans never liked total nudity, despite all the artistic portrayals and public baths; there was always an item of clothing left on by one or both partners during a bit of hancus-pancus.
It sounds strange to us perhaps, but then these are the same people who watched slaves fight to the death for entertainment.
(Can't find the actual quote in the book - it's a mighty tome and a very detailed one).
Thank you. That is a possible explanation, but I am reminded of the notes to explain jokes in the plays of Aristophanes which often appear to have been worked out from reading the plays. Perhaps it is just a suggested explanation prompted by the illustrations. It would be really nice to find a reference somewhere in ancient literature that explains what is going on. You'd think there would be something in Martial, but I can't find it there.