Crystal ward

The Crystal shield is a powerful shield available after a player completes the Roving Elves quest, and a possible reward from this quest along with the Crystal bow. To wield the crystal shield, a player must have 70 Defence and 50 Agility. It can be considered similar to the barrows rewards due to its substantial power and pricey repair costs. The Crystal shield is especially good against Ranged attacks. It also holds the strongest defence against Summoning familiar's attacks.

The crystal shield degrades over time. When a player obtains a new crystal shield, it will be a "New crystal shield". However, after 250 hits, it degrades into a "Crystal shield 9/10", and for every 250 hits thereafter it will degrade another 1/10th, until it reverts into a crystal seed after a total of 2,500 hits. As the crystal shield degrades, its defence bonus drops. Once the crystal shield has reverted to a crystal seed, a player can buy a new crystal shield for the cost of 750,000 coins, or have their crystal seed enchanted into a shield by Ilfeen. While having the seed re-enchanted costs 750,000 coins for the first time, the price lowers each time you get it re-enchanted. The first recharge costs 750k coins, the second 600k coins, the third 450k coins, the fourth 300k coins, and the fifth and every time thereafter costs 150k.

An interesting thing to note is that if you are pickpocketing somebody and happen to fail, the amount they hit you for also counts against your shield's charges. Thus, pickpocketing is an effective way to degrade your crystal shield. The quickest way to degrade the crystal shield is to go into any dungeon that requires a light source with only food in your inventory and the shield equipped. All of the insect damage will count against your shield's charges.

Bonuses over course of degradation
As the shield degrades the negative magic and range attack bonuses remain the same and the other bonuses decrease as shown below.

Trivia

 * Even though it takes only 50 agility to wield the crystal shield, an agility level of 56 is needed to complete the Regicide quest, which is a prerequisite to complete the Roving elves quest. It is however, possible to buy the shield from the Grand Exchange at full charge, but it cannot be wielded until Roving Elves is complete.