Ask HN: What was PG's quote regarding judging value of something?

I can recall that PG has written something on how to value a painting in one of his essay. It went something like: ..I want to make sure I am not biased when judging the value of a painting. Would I still consider worth its price if it was biting dust and being sold by a roadside vendor... My memory is fuzzy so this could be a highly inaccurate phrasing. I am not even sure if painting is what he was talking about. Does anyone know in which essay he wrote it?