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Home > Process > Kiln Firing

Kiln Firing Process

  Sink Firing – Our kiln pictured at left was designed and built by myself following the style of a large graduate kiln at the College of Ceramics at Alfred University. This popular kiln was known as the Big Motha out of respect for its considerable size and occasionally obstinate qualities.

Since it takes all day to load this kiln – the shuttle car style allows the shelving to remain in place with the car pulled into comfortably heated space. The interior stacking area of the kiln is six feet long & high and 2.5 feet wide.

This sizable space is adequate to stack approximately fifty 16 inch diameter sinks with additional smaller ware stacked between each sink. Stacked with smaller cups and mugs the kiln will accommodate as many as 2000 pieces stacked with only the tiniest space between each piece.

Firing sinks takes considerable care because these larger pieces are prone to uneven heating and cooling which will produce stress fractures and even steam driven explosions if one is not very attentive. The typical glaze schedule starts in the late afternoon and continues through the night with the kiln reaching full heat late the following afternoon.

Final glaze temperature is about 1270 degree centigrade – what is referred to as Cone 10 in reference to pyrometric cones that are used to gauge glaze melt.

The average firing cycle of both bisque and glaze consume approximately 250 gallons of propane which is supplied from an external 1000 gallon tank.

The atmosphere while firing is given much consideration as the percentage of oxygen and carbon during the firing determines the final glaze color. Managing and adjusting for proper reduction is a dynamic process that is never precisely controlled.

Car Kiln Car Kiln - This is a frontal view of our car kiln which is situated in a cement block building adjacent to our shop. The moveable track sections are laid through the door opening so the car can be pulled into the shop for loading and the door closed to the unheated kiln building.

The iron frame at the front kiln center supports the door which is mounted on the front of the car which is itself mounted on wheels so that it can be easily rolled along the track sections. Having the car carry the door is quite slick because the kiln door is closed when the car is pushed into the kiln itself.

Car Kiln Door Kiln Front - This view shows the supporting framework for the car mounted door and the angle iron kiln corners held in place by spring loaded rods which allow the kiln to expand as much as an inch in all direction during the firing. The barely visible roof is suspended on stainless steel pipes running through holes in the insulation brick. The kiln foundation is high duty fire brick up to the level of the burner ports and insulating firebrick with higher heat retention for the remainder of the structure. Vent hatches create a cross draft to cool the building.
Car Kiln Burners Kiln Burners - Pictured are five of the ten naturally aspirated propane burners – a set of five situated on each long kiln side. Heat is introduced into the kiln interior where it circulates among the ware and is drawn down to exit at the rear kiln base – in a manner that is described as a downdraft style. The soft insulating brick walls above the burners are a full 9 inches thick – with the exterior brick remaining warm but cool enough to touch at the height of the firing. Each burner has a million BTU output capacity.
Bisque Sinks Bisque Sinks - All of our sinks are carefully dried and then bisque fired at 1060 Centigrade to harden them so they can be safely handled for glazing and then are re fired to full vitrification at 1270 Centigrade.
Car Kiln Shelves Car Kiln - After a 24 hour gradual cooling the shuttle car is pulled from the kiln via the moveable tracks and viewed from the rear after a completed glaze firing. The finished ware shows final bright glazed colors transformed from the dull raw glaze that began the firing 48 hours earlier. The position of the kiln shelves relative to the supporting posts, car bed and door are clearly seen. The hollow floor structure beneath the stack creates draft passage for kiln exhaust heat.
Car Kiln Ware Stack Ware Stack - This close up detail of finished ware shows the thin nitride bonded silicon carbide shelves that were a tangential outgrowth of the Space Shuttle’s heat shield tile development program. This light weight shelving is a wonder after years of using monster one inch thick carbide slabs.

This particular firing contained only a few sinks and is substantially filled with functional production ware for our summer sales shop.

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115 South Gouldsboro Road - Gouldsboro, Maine 04607 - sales@waterstonesink.com - 207 963 5819
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