I am wondering if it would be easier to make a separate copy of the original FCW file, make all line widths zero, then give them a width back in Inkscape.

Looking good :)

Have you considered using a Fresnel shader and the 'Pointiness' input of the coals to shade them?

Here I've made a crude burning coal shader by combining a regular dark stone texture with just such a combination.

Looks pretty good, Jim :)

Thanks for explaining, Remy :)

Oh you won't get any practical help until after 20 June, when I hand everything over for MD ;)

But after that I have breathing space to be more generous.