I have had that happen also Try this
Go to Tools select surface selection.
Open the Surface tab now select the
part of the Sword.that is turning white.
go down the list in surface tab and adjust the Glossiness
of that surface to the 100% all the way to the right
the 100% should turn gray. Also check the next line down
Color if it is white change it to black, now back in tools
select spot render and use your mouse push the left
button and drag over sword, It will do a quickie render
to see if that solved your problem. you can make fine
adjustments now even change the texture.
do the same with the Knife.
That should do it

Lighthorse
FalconArts.Com