We don't have synonyms for ashing yet — it may be a rare, specialized, newly coined, or misspelled word. The closest thesaurus entries we have are aching, lashing and washing.
(n) :
(analytical chemistry) An analytic procedure in which a sample is heated in a furnace to leave a residue of ash, either to determine the gross mineral content, or as a preparation for further analysis
(n) :
(analytical chemistry) An analytic procedure in which a sample is heated in a furnace to leave a residue of ash, either to determine the gross mineral content, or as a preparation for further analysis