"the kind of conversation happening in art"? It is the question on the topic you replied to. It is of direct and clear relevance to this conversation that you are engaging in. What obnoxious imposed pedantry!
I will agree that conservators would be the most likely to know.
Asking what chemicals and processes were used to create the color palate of an artist
is a large part of "interrogating the work". Have you been to the van Gogh museum lately? Or seen his work displayed anywhere? There is often a discussion of his use of unstable pigments and the color changes they have undergone, certainly part of "interrogating the work", as what we see now is a chromatically degraded version of what he saw, in many cases.
And specifically, people are definitely interested in his canvas suppliers:
van gogh's canvas
I like your examples, but not your interpretation. Van Gogh was always working with what he could afford, which fits the question here, and most of the reasonable replies.