Ward Burner Systems

customized combustion equipment

Firing Rates

 

 

by Marc Ward
Clay Times Jan. 2001

 

    Ahh,.....the world just keeps on turning. Last issue, I provided you with a small glossary of terms to help you in your discussions with the local gas people. Well, the first term I gave you was AGA, the American Gas Association, which is, or rather, was an approval agency that dealt with appliance and parts certification for use with fuel gases. They are no longer with us and have been swept up in merger mania. The CSA, no.., no.., not the Confederate States of America, but rather the Canadian Standards Agency, bought the AGA. Like the UL (Underwriters Laboratory), these are private certifying/testing agencies. Effective July 2001, the AGA label will no longer be on parts and appliances (some manufacturers have already dropped the AGA logo). So the label to now look for will be CSA International, though I've been told that the "C" no longer stands for Canada but...no one seems to know what it stands for. Anyway, I'll bet you'll be the first in your neighborhood to pass on this piece of trivia to your local gas folks. Won't you score some points!!? Won't you be a nerd?


    An old customer called the other day. Not that he's old but , he's had our burners for a long time. Well, come to think of it, we all may be getting old.....can I tell you about my grandson?... Seems my old customer has been firing the same way for 20 or 30 some odd years. He's always started the kiln before he left for the evening and candled through the night. He would come in the first thing in the morning an turn the burners on low and proceed to fire for another 12 to 14 hours to cone 10. Loved his pots. His customers love his pots.


    So,.. he goes out of town and leaves the whole kittenkabuddle to his new apprentice, thinking, as most bosses do, that their employees are totally aware of the their every desire. Wrong. The well-meaning youngster (remember we're old and smart) skips the candling,...comes in the morning, lights the kiln and hits cone 10 in about 7 hours, shuts off the kiln and goes home. Our old boss comes back, ..hears the firing schedule and freaks. They let the kiln cool down, unload the pots...... then he calls me.....


    He's a little confused. Not only does he have to apologize to his helper but, his world is a bit askew. All the pots look exactly like they did when the kiln was on for 20 hours (candleing & firing time). He calls me to ask; How is this possible?...He really means; Why have I wasted an additional 1.3 years of my life firing this kiln?


    Potters have an subjective notion of what firing times mean. I always ask the question; 'How long to you want to fire to get to cone x?" They usually answer with; "I don't know...a normal firing time". I then ask, "What's normal?" At this point, the answers range from 6 hours to 36 hours.....  The bottom line is that most potters fire like the people they learned from.


    In industry, fuel savings is the key. This means, the heat energy from the fuel should go, as much as possible, to the ware. You have tunnel  kilns that are masters at this. Porcelain dinner ware enters the kiln cold,...is moved along on a conveyor belt...enters a hot zone...then leaves the kiln... cold.... all in 45 minutes. Wall tile, like your bathroom tile, does this process, to cone 10, in as little as 10 minutes!!!


    The reason our work looks so vastly different from the mug at Wal-Mart is not the firing time. It's the cooling time. Potters build kilns like they did 100 years ago. Nine inches of brick. Big 'ole periodic kilns. Once you heat this mass to temperature, it takes a long time to cool down. 18 hours.....24 hours......This cooling gives the glaze time to develop a crystalline structure. This is what it is all about.. These crystals cause light to pass through and bounce off the glaze in wondrous ways. Handmade pottery has it.... mass produced ware doesn't.


    So,... back to our old friend....it was his cooling time that made his pots the way they were, not his firing time. It's our cooling time that makes our ware what it is. Try this;... Speed up your firing, go home, spend time with your family, let the kiln cool slowly, unload neat pots, be happy.