Enamel paints do not simply dry like other paints, they cure. The curing occurs when the enamel is exposed to oxygen and begins a chemical process that hardens the binder. Heat has a limited effect on speeding up the process, although is handy for certain enamels that are painted upon glass. Most oil-based enamels harden within eight to 24 hours and are cured once they feel dry to the touch. Latex enamels cure from the outside in, so may feel initially dry but can take as long as a month before they are fully cured.
Speed-curing Enamel on Glass
Allow the enamel paint to cure for a full 24 hours on the glass before applying any heat. If you prefer to slow-cure your enamel on the glassware, it can take up to 21 days.
Preheat your oven to 350 degrees F for a minimum of 15 minutes.
Lay your painted glassware carefully on a large baking sheet and place it in the middle of your preheated oven. Do not allow any of the enamel paint to touch the surface of the baking sheet, and do not allow glass pieces to touch each other on the pan.
Time it so the glassware is in the oven for exactly 30 minutes at 350 degrees before turning the oven completely off. Do not remove the pan from the oven and keep the oven door tightly closed.
Leave the pan in the oven for a minimum of five hours before removing the glassware from the oven--it should be fully cooled to the touch. Carefully remove the glassware from the baking sheet.