Quote Originally Posted by Legolas Bow of Athena View Post
Free Star Friday
Gem costs of all medals purchased on Friday will be refunded the next day on Saturday.

That can't be accurate, otherwise people would just buy like 100 medals Friday.
On the beta server I simply got back all the medals I used on Friday. I purchased 12, used them, then received 12 medals back on Saturday.

Essentially, it's a 50% off deal for the whole day.