I'm currently reading an MA dissertation on dyeing techniques, which is very interesting. I was particularly struck by the point that one challenge to recreating historical dyes is that the recipes rely on the use of urine, & we simply cannot know the chemical components of the piss of the past.
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The author is a conservation student in Oslo, but it is not clear to me whether they have come to the topic from history, chemistry, or via another route.
But I may have to revise my conclusions now!
2 persons, Person 'A' continues their normal 21st C diet for 6 months. Person 'B' adopts a historically period accurate diet for the same length of time. At the end, collect urine & perform 2 batches of dyeing.
Otherwise it's just 'in the style of'...not that it matters too much, taste and flavour are hideously subjective so we'd never know how close we got