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Firing- Cu Chi style

November 20, 2012

 The wood fired kilns used in the flower pot factories of Cu Chi Vietnam can be described in many ways however the word that springs most easily to mind is massive. Often found under huge tin sheds and nestled into a hillside many of these multi chambered brick giants are over 70 meters long with as many as 16 chambers. Each chamber might contain 100 flower pots of varying sizes all efficiently stacked inside each other like giant Babushka dolls without the lids.

The kilns

These archaic climbing kilns are beautifully constructed works of art in their own right. The teams of professional kiln builders travel from pottery to pottery repairing collapsed chambers or building new kilns from scratch. The construction involves laying raw (unfired) clay bricks made from the same crude clays that the pots themselves are made of to form chambers reminiscent of a mud wasp nest. Hydraulically pressed; the bricks are left to dry in the sun or stacked on top of an existing kiln to utilize the radiant heat. The chambers are constructed in such a way that the arches are supported by the buttressed walls near the doorways, no steel reinforcing is required. Potteries in hilly terrain utilize the natural gradient of the hillsides to achieve the necessary draught for firing.  If a natural gradient is not available then a hole is excavated and the soil piled up to form a manmade incline. The main firebox is at the lower end and the chimney positioned at the top of the hill to make the most of the draught. The main firebox is at the lower end and the chimney positioned at the top of the hill. Chambers in these monsters are large and one could fit two Toyota Corollas nose to nose in each chamber and quite possibly a scooter or two. The pots are constructed in plaster moulds utilizing wire cut slabs of clay. As water is drawn from the local clay into the plaster mould the pot firms up; the mould is then removed to allow the pot to dry. During the dry season pots may be dried directly in the sun. During the wet season pots dry quite slowly, to speed up the process pots are perched on racks directly over the kiln to make the most of the radiant heat. Once dry the pots are raw glazed (no bisque) and packed straight into the kiln on bricks. Kiln shelves are not used very often if at all. The rubber tree wood used to fire these giants is also dried on top of the kilns. The week-long firings commence at the front firebox of the kiln; often while the rest of the kiln is still being packed. It is not uncommon for a 16 chamber kiln to be firing while the last few chambers are still being filled with flower pots. Often teams of professional kiln firers are employed to guide the 7 day firings.

Typical firing cycle

24 hours may elapse to bring the first chamber to temperature. First a small fire is lit in the front chamber. This small fire is slowly built to low fire chamber one to 1100c. Waste heat from chamber one moves into chamber two. Chamber two is brought up to temperature by stoking sticks through the side of the kiln via a hole that is left in the brick door over a period of several hours. The team of firers move from chamber to chamber over many days until the last chamber is up to temperature. Cones and pyrometers are used in some potteries to assess the temperature however these are expensive tools in Vietnam and many poorer potteries simply use draw trials. These draw trials are very effective and shaped a bit like serviette rings. One removes each trial glowing red hot with an iron rod via the side stoke holes.Peering in through the side stoke holes kiln firers remove multiple trials at regular intervals once the glazes on the flower pots start to exhibit some gloss. These trials are allowed to cool and then compared to trials saved from previous successful firings. Once the melt looks satisfactory the firing is finished and allowed to cool for a few days before the “reveal”. The last chamber is often still quite hot when the first chamber is unpacked however the large thermal mass of these kilns warms the cold air as it filters from chamber to chamber. If it’s a busy time of year the chambers are repacked as they are unpacked and the firing cycle begins again.

 One of the inspiring things about these factories is the team work. There are many specialist jobs such as glazing and packing however there is a real buzz as everyone teams up to support with whatever task is at hand. The multichamber design is quite an efficient method of firing since the waste heat from one chamber preheats the next and on and on the cycle goes until all chambers are fired. The potteries are being moved further and further into the countryside outside Saigon as the city expands. Over 1000 potteries continue to thrive shipping large garden pots all over the world.chris.m.james@tafensw.edu.au

From → General posts

3 Comments
  1. Sounds like a wonderful community of artisans. Have a new found respect for the Vietnamese pots I see in nurseries.

  2. They do look absolutely like wasp nests, don’t they? I’ve always wondered where all those pots I saw in garden centres came from, and now I know. And Chris I know that you can say with confidence that each chamber holds two Toyota Corollas nose to nose because you will have parked them in there yourself, just to see. And probs it wasn’t possible to be absolutely sure about the scooters because someone was borrowing them at the time…
    Pamela

    • The activity around these kilns is not unlike the activity around a wasps nest; busy workers getting the job done. The scooters are the main mode of transport in VN. Cars are very expensive.

      Chris

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