With 75 Smithing, using 375 harmonic dust to make one at the crystal singing bowl in the Ithell Clan district of Prifddinas (giving 375 Smithing experience)
The amount of coins needed to create (and repair) is based on the number of times a crystal weapon/armour seed has been made into an item for coins - the cost is shared over all crystal weapons and shields. The first time costs 1,000,000 coins, and each subsequent creation costs 200,000 less until the fifth time (and every time thereafter), when it costs 200,000 coins.
Additionally, a 20% charged crystal ward is a possible reward of Roving Elves, and fully charged wards can be bought from Islwyn in Isafdar forest for 1,000,000 coins (this price does not reduce).
The crystal ward will revert to seed after 50,000 charges of combat, but uses two charges per hit except while within Prifddinas, where it uses one charge per hit. A partially degraded ward can be recharged for a fraction of your current creation cost - if it has 90% charges remaining, and the lowest creation price has been achieved, it would cost 20,000 coins to repair.
Even though it takes only 50 Agility to wield the crystal ward, an agility level of 56 (although temporary boosts may be used) is needed to complete the Regicidequest, 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.
If a player attempts to cast low level alchemy or high level alchemy on a Crystal shield, they will receive a message saying 'You can't do that to elven crystal!' because of a bug allowing you to alchemise a recharged crystal armour and weapons in Free to Play worlds for 900,000.
After the EoC update, there was a bug that the shield didn't degrade in combat. This has been fixed.
Until the release of Prifddinas the Crystal ward was called the "Crystal shield".