Which reminded me of an early paper on local reduction. (ref in  https://community.ceramicartsdaily.org/profile/34897-peterh/ ) One of the most interesting ideas was the use of a SiC containing under-glaze (or IIRC body)  which then influenced the colour of a SiC-free glaze applied over the bisqued piece. - They give under-glaze/glaze combinations for copper reds at cones 012 and cone 9. - They suggested that silicon carbide achieves reduction-effects over this remarkably wide range by