(from PW18 tracking)
For most instances, this should be "careful".
This has been largely completed already for casting recipes in FA18: translating "curieux" as "careful" (rather than scrupulous or curious).
Do a quick check to see if this is consistent.
See for example: p062r4, p084r1, p085v4, p141r1, p157r_3
Search term: curieu
Translated as "careful"/"carefully" in all instances except 84r and 107v where "scrupulous" seems apt:
84r sieve it again, yet without being scrupulous to render it so fine,
107v do not be so scrupulous an observer of the mixture put here that sometimes you would not diminish the quantity of alum de plume