Time doesn't matter. Temperature is important. When you put the product in the oven, the temperature drops, then rises. It is important to monitor the temperature and know what temperature is needed for what color. It depends on the manufacturer and the color itself. Always check the color before using it in a product. Make samples on metal. In total, the firing time is about 2-3 minutes.
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Enamel should be washed with plain water from dust and dirt. Put some enamel in a container, cover with water and stir. wait a while for the enamel to settle and pour out the water. So repeat several times until the water in the bottle is clean.
