Most white gels cure but they have to be fairly thin because the white pigment in the gel prohibits the pigmented gel from curing as well as a clear gel does. This is a result of the white pigment not allowing the UV light to penetrate too deeply into the gel. Think of it this way — white reflects light, right? So, if the pigment in the gel is reflecting the light, then the UV light cannot penetrate deeply into the gel to get it to cure unless the white gel is applied thinner and cured under the UV light.
I instruct my students in the classes I teach to apply the white gels onto a form and cure them under the UV lamp. Once the gel is done curing, I have the technicians clean the cured gel, gently peel the gel from the form, and examine the side of the gel that was against the form. If the gel is still liquid, it was applied too thick and the UV light did not penetrate through the thickness of the gel to get it to cure completely. I have them repeat the process, but this time they apply the gel thinner and examine it for a complete cure. — Jim McConnell is the owner and lead chemist of Light Elegance.