https://www.nationalgallery.org.uk/about-us/partnering-with-...
At that time, you could also just check out a piece and leave a little card there saying you’d taken it.
https://en.wikipedia.org/wiki/The_Work_of_Art_in_the_Age_of_...
One might also note that even seeing an artwork like this in the modern public galleries that we have is quite odd. Altarpieces invite repeated contemplation by the worshippers in a church, over a long time. Maybe you grow up liking the look of baby jesus but as an adult start to notice and think that Mary is smiling down on you in your troubles. In a gallery, you shuffle along in a sea of people, and get a few seconds to look at the piece before your attention is captured by another piece in the same room.