Upgrades can imbue certain items for reward points, increasing stats. The imbued black mask enhances Magic accuracy, Ranged accuracy, and Ranged damage to assigned Slayer targets. The imbued Fremennik rings increase stats, and imbued crystal equipment will not have its stats lowered as it degrades. For crystal equipment, each charge costs an additional 2,000 points to imbue; 2,000 points for 1/10 and 20,000 points for an unused one.
Imbuing it will add an (i) to its name and will have an "Uncharge" option. The uncharge option removes the imbued bonus, and will refund most of the points back. Dying will cause your imbued item to lose its charges, and the player will have to obtain the charges again to imbue it.
source: http://2007.runescape.wikia.com/wiki/Nightmare_Zone