They do not double the experience given for making tiaras. The Runecrafting gloves do not work at Ourania altar (i.e. the bonuses do not stack), since Ourania altar (ZMI altar) already gives double the normal experience of the runes crafted.
The gloves will disappear after 1000 rune essences or pure essences are crafted, and are incapable of being recharged. The message for their permanent destruction is: "The charges in your gloves have been used up, and they crumble to dust."
The gloves's experience-doubling abilities can be compatible with the powers of the Explorer's ring (basically meaning you can get double the Runecrafting experience while you get extra elemental runes from the Ring's magic).