arcanite hardens to mithril not viceversa
meteoric steel or unicorn horn (but it think that needs 25 int to socm into)
with 25 int your best bet is socm into glass and harden to illithium (225 str, 6000 density vs 2000 str 5000 density for mithril
I wiz moded it and flaming illitium sword +3 is Dam 6-12 extremely accurate very strong
whereas flaming mithril sword +3 is Dam 6-11 extremely accurate very strong
of course if you are just going in to face elpuri soon dont forget about ommel tooth which needs only 10 int
flaming ommel tooth sword +3 is Dam 7-13 extremely accurate almost unbreakable and should last many days