If a case colored reciever (on an Ithaca 4E in particular) has been blued can the bluing be removed and the case colors restored?

More related questions:

1) After the case colors are back on should I expect the engraving to be severely degraded

2) How are case colors put on?

3) How is bluing removed from engraved receivers? (I have read that Heinz Ketchup is wicked on blued barrels!)

4) What makes the case colors go away? Routine cleaning? Exposure to air? Combination of both?