Common sense for kiln users

If you are kilnforming glass, you need to be familiar with how to use kilns safely, efficiently, and practically. This section covers some commonsense advice on what you need to be aware of.

Positioning a kiln

Be it floor or bench mounted, a kiln should be supported on a solid base and set up so that the hearth or kiln shelf is as near level as possible. Glass will flow down hill if this not done. If bench mounted on laminated or wood surfaces these should be protected by fibro cement sheet or other heat resistant material.

Kilns should be mounted so that the glass, or the top of the opening on top loaders, are at a convenient working height for the particular operator. 

They should be placed in a sheltered location, out of winds or strong draughts. The chill effect of winds can increase power consumption considerably.

Sensibly, kilns should be located away from heavy traffic areas.

Make sure there is a convenient bench or shelf nearby to facilitate loading & unloading the kiln.  

Provide adequate clearance between the kiln and combustible wall surfaces. 100 to 150mm (4" to 6") is recommended for well insulated kilns, somewhat more for thin wall kilns.

Make sure a suitable power outlet is located close to the kiln. Preferably this should be on the wall behind and to one side of the kiln. It is best to avoid using extension cords to a remote power point as the cords are often under rated and can overheat. They also pose a safety hazard if run across the floor.

Heat and kilns

There are several common sense things to be aware of when using a kiln.

• Kilns can get very hot on the outside and can inflict painful burns if touched at the wrong time.
• Hot air coming out of an open vent or spyhole can be extremely hot. Check with a hand before putting an eye too close to a spyhole.

• Kiln shelves should never be placed directly onto the floor or hearth of a kiln. Always prop them up at least 20mm (3/4") so that air can circulate and both sides of the shelf will be at a similar temperature.

Venting the kiln

This is allowing for the escape of gases produced by the combustion of organic matter contained in the kiln load. and is a normal procedure when firing pottery, but is less frequently needed when kilnforming.

However, the organic binders in fibreboard, CF paper, (as well as unknown products used by individual kilnformers) may produce such large volumes of gas that special provision must be made for their escape.

A small amount of CF paper requires no special provision but, if first firing a fibreboard or Ceramaguard mould, leaving a vent part way open until the kiln reaches about 500°C (930°F) is advised.

Venting is also a standard practice in casting where plaster-silica moulds are being used as glass formers. This ensures that any residual moisture in the mould body is able to escape from the kiln.

With top loading kilns without a lid vent, prop up the lid with a thin piece of refractory material such as an offcut of fibreboard. Be sure and remove it when venting is no longer needed; otherwise it may have trouble reaching soak temperature. 

Troubleshooting

Those with a new kiln should receive operating instructions sufficient to allow them to operate the kiln with confidence.

What may be less adequately covered are things which can go wrong, either through vagaries of design, malfunction or the process of equipment aging.

Interlock switch

Glass processes happen in a box—the kiln, mostly when it is closed.

Kilnformers on occasion, have reasons to open the kiln when a firing is in progress;

• to check on th state of the of glass;
• to load glass;
• to intervene in the heating and cooling cycle; or
• just because plain curiosity gets the better of them.

Opening a kiln presents a range of safety issues associated with radiant heat and electric shock.

Kilns makers are familiar with these issues and  have some built in features that ensure safe kiln operation. AS/NZS 3820:1998 "Essential safety requirements for low voltage electrical equipment" mandates that all kilns be fitted with a device to stop power to the elements whenever the door or lid is open, or the hood is lifted.

A common name for this device is an Interlock switch and they come in many forms and in numerous places. Each user should familiarize themselves with the method of operation and adjustment of the  interlock switch on their kiln.

If a kiln won’t heat up, or cuts out during a firing; first check the interlock switch.

Entering time in digital controllers

Manuals accompanying kilns should give comprehensive information on using the controller. Entering temperatures will generally pose no problems, but entering step times can often cause concern.

Time is usually entered into instruments with four digit displays in hours and minutes. Thus 01:30 represents 1 hour 30 minutes, or 00:01 represents one minute. A problem can sometimes occur with 00:00 or zero time.

Care should be taken when entering 00:00. In some instrument logic this will be seen as zero time whilst in others it can mean infinity.

Consider that you want to heat to a soak temperature and then to switch off immediately.

• If 00:00 time is entered, in one case the power will be turned off immediately; whilst in the other the kiln will hold at soak for however hours or days the kiln is unattended.
• Entering 00:01 is quite safe and unambiguous.

This is much less likely to occur with programmable controllers which store patterns.

If you are unsure of which system applies to your controller, do not enter 00 minutes but enter 01 minutes. this will have little effect on the length of the firing, but will ensure that it does not stay in an infinity phase.

For more on these and other matters relating to your kiln see 25. The kiln. A closer look.