WLN: Whatever they analysed and how they analysed it affects the validity of said analysis.
SC: Gorlitz had analysed that small piece of paint (and its sub-surface) in the images posted. That is what we're told. We have to take it on faith that that is what was analysed. Are you suggesting the laboratory doesn't know how to analyse such samples to determine their chemical properties/composition?
Now THAT is what you call "NONSENSE".
But you're actually right about one thing when you say "...the variable nature of limestone". Because this limestone roof block does indeed vary. It's varied because it has a plaster layer on top of the natural limestone and Gorlitz simply didn't dig deep enough into the roof block to extract any of the calcium carbonate into his sample.
Those marks are painted onto a layer of plaster. End of story.
Edited 1 time(s). Last edit at 10-Feb-19 19:19 by Scott Creighton.