TL;DR: To successfully glaze and fire a porcelain vase, apply a thin, even layer of glaze over the bisque-fired body using a dip, brush, or spray method, ensuring the foot is wiped clean to prevent sticking. Place the vase on a kiln shelf with adequate spacing and fire to your specific glaze’s recommended temperature, typically between cone 6 and cone 10 for standard porcelain, while monitoring the kiln closely to avoid thermal shock.
Preparation and Safety
Before beginning, ensure your porcelain vase has completed its initial bisque firing. This step strengthens the clay body and makes it porous enough to absorb the glaze properly. Wear appropriate personal protective equipment, including a dust mask and apron, as glazes contain chemicals that should not be inhaled or touched directly with bare skin. Work in a well-ventilated area to maintain air quality and minimize the risk of inhaling fine particles. Check the surface of the vase for any cracks or defects that could cause the piece to fail during the glaze firing process. If you find any flaws, repair them now or discard the piece, as glazing over cracks will likely result in a broken vase after firing.
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Applying the Glaze
Choose a glaze specifically formulated for porcelain and compatible with your intended firing temperature. Mix the glaze slurry according to the manufacturer’s instructions, ensuring it is free of lumps. For a uniform finish, dipping is often the most effective method for vases. Submerge the vase slowly into the glaze bucket, rotating it gently to avoid air bubbles. Alternatively, use a large brush for more control over color placement and depth. It is crucial to wipe the bottom foot of the vase with a damp cloth or solvent to remove all glaze residue. Any glaze left on the foot will melt and stick to the kiln shelf during the high-temperature firing, potentially ruining both the vase and the shelf. Allow the glazed vase to dry completely before moving it to the kiln, which usually takes twenty-four to forty-eight hours depending on humidity levels.
Firing the Kiln
Load the kiln carefully, ensuring there is sufficient space between the vase and the kiln walls as well as other pieces. Overloading can lead to uneven heat distribution and thermal shock, which often causes porcelain to crack or explode. Use kiln wash on the shelf to protect it from potential glaze drips. Set your kiln controller to the appropriate firing schedule for your specific glaze and porcelain body. Most porcelain glazes mature at high temperatures, typically ranging from cone 6 to cone 10. Monitor the firing process using a pyrometer or kiln cone to verify that the correct temperature has been reached. Once the firing is complete, allow the kiln to cool naturally. Do not open the kiln door until the temperature drops below two hundred degrees Fahrenheit, as rapid cooling can cause the porcelain to shatter due to thermal stress. After cooling, inspect the vase for any crazing, pinholes, or other defects, and clean the surface with a soft cloth if necessary.
FAQ
Q: Can I reuse glaze from a previous batch?
A: Yes, you can reuse leftover glaze if it has not dried out completely or been contaminated with foreign materials, but you must strain it through a fine mesh to remove any lumps before dipping or brushing the new vase.
Q: Why did my porcelain vase crack during the firing?
A: Cracking usually occurs due to thermal shock from opening the kiln too soon, uneven heating caused by overcrowding, or pre-existing cracks in the bisque-fired body that expanded under heat.
Q: How do I remove glaze from the foot of the vase?
A: Use a damp sponge or a cloth soaked in solvent to carefully wipe the bottom edge of the vase immediately after glazing, ensuring no residue remains to prevent it from fusing to the kiln shelf.
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