Frequently Used Terms

Safety

Propane vs. Natural Gas

Gas Kiln Maintenance

Gas Kiln Troubleshooting

Updraft Gas Kilns

Downdraft Gas Kilns

Atmosphere in a Gas Kiln

Olympic Gas Kiln Manual 

 

Frequently Used Terms

 

BISQUE – The term given to ceramic ware which has been given a preliminary firing prior to glazing. Also called biscuit.

BURNER – A device in which air is combined with gaseous fuel and ignited at the burner tip.

BURNER BLOWER – An air fan, or blower, is used to provide air in quantities greater than the natural draft situation provides. This allows a greater amount of heat to be obtained from a burner of a given physical size.

BTU BRITISH THERMAL UNIT – 1 Cubic Foot Natural Gas = 1000 BTU / 1 Cubic Foot Propane = 2,200 - 2,500 BTU

CANDLING – The gradual heating of the kiln usually overnight, with a low flame (candle-size). The period of slow  drying of the greenware before the kiln temperature is increased at its programmed rate. Omission of the candling period can likely cause explosion of greenware when the moisture expands as steam.

CLAY MATURATION POINT – Clay, or more appropriately, a clay body, when subjected to heat treatment, fuses and undergoes chemical changes which modify its strength, porosity may define the clay maturation point.

CFM – Cubic feet per minute, refers to volume of gas flow.

CFH – Cubic feet per hour, also refers to volume of gas flow.

COMBUSTION AIR – The total air intake to the firing chamber, which is used for combustion. Combustion air has two means of getting into combustion: Primary air: Air passing through the burner. (The air mixing plate controls the primary air intake. Secondary air: Air entering around the burners through the top of the burner and the bottom of the kiln. There needs to be 1/2” space between the top of the burner and the bottom of the kiln.

CONE – A ceramic composition in the shape of a pyramid about 2 ½” long (Senior or Witness Cone), which bends as a temperature is reached over a given time period. The cone is said to have reached an “end point” when its tip
bends over and touches the surface upon which the cone is resting. The cone temperature is quite random with unequal temperature intervals between cones. A standard cone’s composition varies according to its intended melting temperature endpoint, and thereby so does its color vary. The cone number may really only be determined by the number stamped on each cone or by testing procedures beyond the capability of the average potter. The small or Junior cone (1 1/8” h) was especially developed for the kiln sitter and should be used only in kiln sitters and not as a witness cone.

DAMPER – A cover (brick, kiln shelf, etc.) used to partially restrict the exhaust opening from the kiln. This controls the heat escaping and the fresh air entering the kiln. Proper adjustment of the damper is evidenced by continual temperature increase without increasing the gas flow to the burners. A damper also restricts air into the burner.

DOWNDRAFT KILN – A more complex system than the updraft kiln in that the exhaust as well as the intake is at the bottom. The heat may be exchanged to the ware on both its up going and down going paths. It requires a chimney or stack to induce enough draft to pull in fresh air for combustion.

FURNITURE – The shelves and posts which are used to stack ware on multiple levels while firing the kiln.

GREENWARE – Refers to any unfired ceramic ware, but usually in the dry state.

HEAT TRANSFER – Heat energy is brought into the kiln by way of the fuel. The heat is released from the fuel by combustion (burning) and is absorbed by the bricks, shelves, ware within the kiln chamber. Likewise, heat is transferred from the inside of the kiln through the brick walls, to the outside air, where it is lost for productive purposes. This is called heat loss.

HIGH LIMIT CONTROLLER – An electronic device to control kiln shutting off when a firing is finished. The kiln operator sets the target temperature, and when reached, the controller will shut the kiln down. 120 volt outlet required.

KILN SITTER – An automatic shut-off system used for bisque and glaze firings, and as a safety device when doing reduction firing.

INCHES OF WATER COLUMN – A unit of pressure: 1” of water = .577 ounces/sq. in.; 1” of water = .0631 pounds/sq. in.

ORIFICE – An opening through which gas passes into the burner. Orifice size determines the heat output of the burner; i.e., BTUs – propane due to the higher output will have a smaller orifice than natural gas.

OXIDATION FIRING – Occurs in a kiln combustion atmosphere with approximately 6% excess oxygen. This is the most common kiln firing. An electric kiln normally has an oxidation atmosphere. A gas kiln must be adjusted for this atmosphere.

PSI – Pounds per square inch. A unit of pressure.

PYROMETER – An instrument that enables accurate temperature monitoring during the kiln’s firing.

RAKU FIRING – Raku, a Japanese word often interpreted as “enjoyment” or “happiness” is a form of ceramic art in which a piece is subjected to a post-fire reduction process using sawdust, paper or other materials to change its color and chemistry. Raku artists value the technique for its ability to produce a wide range of colors and effects – since no two pieces of raku pottery ever look alike.

REDUCTION FIRING – Occurs when the air supply is restricted to an amount below that needed for complete combustion of the gas present, resulting in a consumption of oxygen from the clay and glaze compounds. Reduction produces colors based upon the metallic compounds in the clay and glazes rather than the oxides of these metallic compounds.

REFACTORY – Materials which will withstand high temperatures, and includes fireclay products, firebrick, shelves, and posts.

SOAKING – The process of bringing a glaze to maturity, i.e., a cone end point, and holding it at that temperature to allow the bubbling and pinholes, which are a natural part of the glaze process, to heal over and become smooth. Soaking is also used for crystal growth. Proper time determined through experimentation.

SOLENOID GAS VALVE – An on-off gas valve, which is electrically operated.

THERM – A heat energy unit being used by gas companies because the cubic ft. per hr. measure does not properly describe energy usage. 1 Therm = 100,000 BTU.

THERMOCOUPLE(S) – Two types of thermocouple may be used when firing a gas kiln. The first type is the one used with a pyrometer or electronic wall unit. The second type of thermocouple is for the magnetic baso valve on a gas kiln. This thermocouple senses the temperature and flame from the pilot light and causes the magnetic baso valve to open when the kiln is firing and is used as a safety device to shut down the kiln when there is no flame on the pilot.

UPDRAFT KILN – A gas kiln that introduces heat at the bottom and exhausts at the top. It does not require a chimney to induce a draft. The heat is exchanged to ware while passing from bottom to top.

WALL UNIT – An electronic controller which runs the kiln firing after manual adjustments.

 

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Safety

Your Olympic Gas Kiln has been built to fire at high temperatures and to run on natural gas or propane. Check with your local municipality to determine any codes you may need to follow to install a gas kiln. A few notes before you begin firing your gas kiln will add to your enjoyment and safety. Your gas kiln should be installed on a concrete, masonry or brick floor that is non-combustible. Keep all flammable materials at least 6 feet away from the kiln and do not use highly flammable, combustible materials around the kiln such as gasoline, paint thinner, etc. The surface of the kiln is hot and individuals should not touch the kiln when it is firing.

LIGHTING – The flame source (blow torch, gas match, fireplace match) needs to be long enough to keep the operator well away from the burner openings. When lighting, keep kiln door or lid open.

VENTILATION – A room must have adequate airflow into the room and exhaust gases must be vented in accordance with local requirements or codes.

GAS LEAKS – Whenever gas piping is modified, it should be pressure tested and at the same time soap tested. Never check for leaks with an open flame.

KILN WATCHING – A gas kiln should not left unattended.

FIRE EXTINGUISHERS – The best extinguisher for a gas fire is to turn the gas off. Make certain that everyone in the area knows where the gas valve is and how to turn it off. If the valve requires a wrench, hang it nearby. Fire blankets, sand pails and appropriate extinguishers should be available and everyone involved instructed in their use.

OBSERVATION/PEEPHOLES – Care should be used when viewing through the kiln’s observation holes.Safety suggestions are never complete and every situation will not be covered. Above all, use common sense and good judgement when firing your gas kiln.

If propane is used, your tank must have a low-pressure regulator like those on a camper or trailer. If an adjustable regulator is used, approximately ½ pound of pressure is necessary.

 

Natural Gas

A larger burner orifice in necessary when used on natural gas pressure, six (6) to eight (8) inches of water column is required. If your kiln was ordered for use on household natural gas, it is equipped this way.

The natural gas pipeline that connects to the kiln needs to be one that has a ¾” inside diameter.

Assembly of Kiln

Olympic Torchbearer kilns are built in rings and may be detached and reattached when moving from one location to another.

When handling your new kiln rings, always be sure to grasp the rings by the outer surface only.

Do not grasp the bricks as they are made of a porous material and may chip in your hand. Raku kilns are shipped fully assembled.

After making certain the stand is level, adjust the burner manifold so the pipe section on top of each air mixer is approximately ½ inch below the bottom of the kiln. The kiln bottom must be positioned on the stand so each burner is directly beneath one of the holes.

It is recommended that the burners be positioned with the gas valve on the right side when you are facing the kiln, however, if it is more convenient to place the manifold in another position be sure to align the burners with the holes in the kiln bottom.

Venting Torchbearer and Raku Kilns

Proper ventilation is required when firing a gas kiln. Gas kilns fired outside may not require a vent. When purchasing vents it is often best to choose a local HVAC or sheet metal manufacturer, or Olympic Kilns can manufacturer one for you. Vent dimensions need to be round or square in a cone shape and the bottom of the vent needs to be larger than the outside diameter of the kiln. Diameter at the top of the vent needs to be 10" discharging into an exhaust pipe required by building conditions or local codes.

 

The vent needs to be placed 18” above the kiln when the lid is open or above the kiln frame.