Craftmanship In Clay: Stacking And Firing (1949)

today just as in the past man creates pottery from clay and fire after the clay pieces have been formed it is the firing process which hardens them and melts their glaze to a smooth glass-like finish both glazed and unglazed wear fired in the kill at the same time to show the steps in the firing process these two pieces can be compared with an unfired one all were identical to begin with the dry unfired clay piece called Green wear when fired becomes bisquare glaze is then applied the more obvious changes caused by firing are in color in size and in hardness in order to reach the high temperature necessary to harden clay and melt Glaze The Potter uses a kill which is simply a chamber lined with fire brick and some means of being heated the small kills used in most studios are heated by gas oil or as in this case electricity before the kill is stacked with Pottery to be fired the shelves made of fire clay must be carefully inspected for glaze drippings from previous use these drippings would fuse to the bottoms of pieces in later firings so they must be chipped off fresh kill wash is then applied to the spots the kill wash composed of clay and Flint does not Harden in the fire and thus permits glaze drippings to be chipped off easily before being fired green pottery must be thoroughly dry damp pieces usually feel cooler than dry ones more green pieces can be fired at one time if they are stacked together according to size and shape shelf supports should be selected to make the use of the kill space the short shelf support will conserve space and can be used if the pieces are rearranged to fit the Potter must use his Ingenuity in arranging the pieces to get as many as possible additional shelf supports can easily be cut from a porous fire brick for each firing the kill shelves are rebuilt to accommodate the pieces to be fired there is less danger of damage to the pieces if the heavy unwieldy shelf is already in place each piece or group of pieces must be carefully checked for height before it is placed in the kill green pieces May touch each other or the interior of the kill but must not touch the heating elements along the bottom or sides of the kill because of the intense heat of the elements during firing cups or bowls of identical shape if nested often stick together instead stack them rim to rim pieces to which glaze has been applied must be fired without touching each other or the interior of the kill usually each piece is supported on a fire clay stilt which can be double pointed or single pointed triangular fire clay plate pins can also be used for support when plate pins are used in this way the bottom of the piece must be carefully cleaned of all glaze firing box covers close to the boxes will ensure a better fit after firing since shrinkage differences will be less a double pointed stilt is used for the majority of pieces if the stilt is proper size the points will touch only the unglazed foot Rim if a piece set on a stilt is slightly high when compared with the shelf support the substitution of plate pins May lure it enough to fit in the rear of the kill where stacking is difficult a piece can be placed accurately by first gently touching the back wall then withdrawing the piece at least one4 of an inch a block of porous fire brick cut to fit can be used to support a piece in space that might otherwise be wasted if the foot Rim is absolutely clean a large plate can be set directly on the shelf and is less likely to warp glazed pieces must have at least 1/4 in clearance between them where this spacing cannot be readily seen the finger can be used as a gauge a piece with a fully glazed bottom must have a double pointed stilt these parametric cones are temperature indicators at predetermined temperatures they soften and bend down one pair set upright in a clay Pat is used for each firing this cone bends first as a warning then the second cone bends and the heat must be shut off cones previously fired in various parts of the kill have been used to make this heat distribution chart this guides the Potter in placing each piece according to its heat requirements the cones must be placed where they will be clearly visible through the pee pole during firing with the kill now stacked a final check is made on the actual visibility of the cones before the door is closed after turning on low heat the Potter records the time the early stages of firing must progress slowly not until the interior of the kill is cherry red is it to increase the speed of the firing hourly observations are made until the warning cone is down then a closer watch must be kept until the end of the firing for The Potter Knows that careless firing can destroy his work if the kill were turned off too soon the glaze would be rough and bubbled reiring to the proper temperature would remedy this but not all firing errors can be remedied a damp piece would be shattered by the heat of the kill if space were not allowed for the bending of the cone it would refuse to any piece it touched this condition called slumping so when the second cone is down the heat must be turned off Hill must not be opened until it is cool the time allowed for cooling should be at least as long as the firing time which in this case was 7 hours and 35 minutes with the termination of the cooling period awaited moment the moment door is CR ious L opened the finished beauty of the Potter's art good shelf Arrangement correct sport for each piece accurate placement in the kill and carefully controlled firing and cooling are all a part of good craftsmanship the kill is an essential tool of the Potter for out of it coming of lasting Beauty