I used to toss 'em into a shrine to get rid of the empties, but during this last test, mine disappeared with the last use. I'll probably use mine more often at projects if I happen to be there at the right time.
They just vanish when they're used up. Least I'm fairly positive that's what mine did.
I use up lots of them, but I do spend a ton of time in the tower and end up replacing what I use and then some.
Maybe they will have more of a use later on in the game? I think that will apply to lots of items as the world grows. When I got mine from the tower, I just let it sit there incase I did something stupid and wasted it - I figured as you had to go through so much to get it, it had to be pretty special...although I wasn't quite sure what it was for either at first LOL
@Violet
Like MaryLiLamb, I get them sometimes while gardening. Otherwise, there's a quest in Rm23 of the Tower in Jethimadh where you can get the Random Kindness as a reward. The quest is repeatable for 100 currants.
I have one that has never gone away. Just sits there, empty and useless yet pretty.
Only recently I got another (most likely during a manic gardening episode) and haven't used it up yet. Will see if it goes away.
Mine have all disappeared when used up, think it would be great if we could recharge them! The focusing orb with some energy loss would be acceptable for me. Have only got them in the tower. On the other hand, if they are going to show up more often (as in gardening) then maybe that isn't necessary.. Looking forward to my garden becoming beneficent in this way :)