Ethersworn Shieldmage

• WOTC Official Reminder Textofficial rules
  Flash — You may cast this spell any time you could cast an instant.

• WWizards of the Coast2009-05-01
  Official Ruling
  When Ethersworn Shieldmage’s triggered ability resolves, it doesn’t lock in which permanents will be affected. For the rest of the turn, any time damage would be dealt to a permanent, check whether it’s an artifact creature at that time. If it is, that damage is prevented.

Rulings via Scryfall