I am aware that advanced chemical synthesis and the like are well beyond the reach of Luperci, but what about more rudimentary things like adding (rare and expensive)ground metal dust to fire to make it burn different colors? Or making little bundles of flint and leaves that spark when thrown?
For instance; could a skull be carved with patterns, have those patterns filled back in with flammable tree resin, and then covered up with powdered egg or bone so that the resin lines aren't visible. Then when the skull is lit on fire, it would appear to 'magically' have markings burned into it.
Or is this just too labor intensive to be believable?