As promised, I had a play with my gel pens last night on one of the black Zentangle® tiles. Fair to say the white comes up well (I dont have the white Sakura Gelly Roll which I am told gives the best results) - the Inkssentials one better than the Signo. The glittery and glaze ones not so well, but the real winner was the Sakura Souffle pens! When they first went on, they didn't show up so well but once they dried, they look fantastic! They have totally motivated me to try some other ideas too.