I put this in the feedback section but feel it would be better placed here as well.
I think flux should be able to be made from multiple sources outside of herbalism. Since flux can be coal.
(Source: http://en.wikipedia.org/wiki/Flux_(metallurgy))
Also, flux in mortar confused me, as mortar, if you ask me, should be a set of simple materials (Such as combination of Sand+Clay+ water)
"The first mortars were made of mud and clay. Because of a lack of stone and an abundance of clay, Babylonian constructions were of baked brick, using lime or pitch for mortar."
Source (http://en.wikipedia.org/wiki/Mortar_(masonry))
I am hoping they refine this process and use flux appropriately in the future as doing it through herbalism does not really make sense in the above contexts.