As far as I know, it'll glow forever. 
Awesome Does it only come in white as far as you know? I've only ever seen it in white, but I have an idea but I need coloured glowing clay...
Does it only come in white as far as you know? I've only ever seen it in white, but I have an idea but I need coloured glowing clay...You can color it using another color of clay, or chalk pastels.
I don't have pastels, but I can like mix some red clay in and it should mix and make the red glowy?