Quote Originally Posted by RichardH View Post
Have acquired a selection of old dies all of which are covered with surface rust, before I either blast them with plastic media or immerse them in acid is there a better way of dealing with it?

I can't be the first in this situation?
Dilute phosphoric acid to eat the rust even where you can't see it, thorough rinse and then into that water displacing oil stuff you have.

Then see how the surface roughness on the inside of the die affects the cases you run through it.