Be aware that Royal Alchemists found the way to restore some of Philosopher's Stones spent for items improvement. This weekend - two days only! - you will have opportunity to use results of their experiments.
For every five Black, White or Red Philosopher's Stones you spend, you are getting one stone of the same colour!
The promo starts at 00.01 GMT June 24 and up to 23.59 GMT June 25. Any Stones used before or after this period don't take part in the promo.
Look for details here: https://us.royalquest.com/forum/index.php?/topic/2687-stones-come-back/