This item can be taken to Mr Ex to have him seal the jar. Doing so will prevent the jar from opening before the player dies. Doing so will also prevent the purchase and/or use of the Book of diplomacy, thus making the account permanently Ironman status even after death. Doing this is in no way reversible, so make sure this is definitely what you want before having him seal it. Sealing the jar is also unnecessary to make the jar work. It will automatically make the account a normal Ironman upon death as long as you own the jar.
When you die and return as a normal Ironman, you will lose all but 3 of your items and have no way to reclaim the rest of your lost gear.