Kirby & Spring information on 93v_2: Le plus delie est le meilleur pour travailler Il se subtilie en le lava{n}t “The most delicate is the best for working. It is refined by washing it.” This last phrase highlights some challenges in translation; “Il se subtilie” is here translated as “It is refined” and in the digital edition as “It is thinned,” but the literal translation “It is softened” is hard to understand. An English treatise of 1573 in similar archaic language is helpful in this respect. The author advises to choose smalt “which is bright of colour, and not harshe, but softe betwene the fingers.” Marshall Smith, too, a century later states “the best Smalt is the deepest and soft like Butter between the Fingers.”
Based on this information, we should consider changing the translation.
Perhaps best version: "It is made finer by washing it"
subtilie used as a verb -- to be translated as "make finer" -- should be reconsidered throughout the ms
search for subtil* in oxygen as a start