Firing Tips for an Olympic Updraft, model 2827G, 10 Cu feet:
These notes reference model 2827G which has 10 cubic feet of space and four burners.
1. Use a dual pyrometer setup -- one probe in top peep and one in bottom . I prefer digital.
2. Place a cone pack on top and bottom shelf .
3. Use flames spreaders on two of the four ports (a two inch post on each side of the port with a 5 inch post laying across them).
4. Bottom shelf is 4" above floor . Half shelves are spaced about 1inch apart and usually staggered to aid flow. Don't allow pots to split into the space between the shelf and the kiln wall as you don't want to block flames up the side. It is ok to have pots sticking into the one inch break between half shelves but this is not for plates or large bowls as they will warp.
5. Do not load the kiln too tightly. It is important to get good draft flowing thru the kiln.
6. Use a baffle shelf at 1 1/2 inch from inside of top vent, but be careful that the baffle is not so large that it inhibits the draft flow. If the draft is stalled you'll see symptoms like stalled temperature rise or the kiln will shut off due to overheating of the thermocouples. I've found it also helps to prevent overheating if you turn down the pilot as you increase the gas pressure during the firing.
7. I use two smaller half shelves from a raku kiln on the top of the kiln to adjust port air outside on top. I use these as dampers to induce and control reduction.
8. The air adjustments on burners are very important. Once set, leave them alone. Mine are set at one forth inch. They appear to have significant control over the amount of reduction.
9. Peeps should be plugged.
10. The firing schedule I use is a fairly rapid initial rise to 900 degrees centigrade over three hours. I start reducing when the cone 012 falls. I control reduction and firing rate by increasing the gas flow and adjusting the top damper. It seems to take adjustments to both to get an even firing. Quarter inch marks on the kiln top help measure the damper position so you can repeat. I guage the amount of reduction by the color/volume of flames out the top and out the peeps. A heavy reduction will have flames licking out all peeps and the top.
11. Firings run 8- 12 hours with a natural cool down. I watch pyrometers until about 2100 degrees, then watch for the cones to fall. Early in the cycle, the bottom pyrometer measures 100 - 200 degrees higher. Once reduction is induced, the temperatures converge.
12. I had a flow gauge added to the gas line so I can be more precise and create a repeatable pattern when increasing gas. To date, I rarely open the gas guage above 2" of water pressure. I am using natural gas under 2 lbs of pressure at the meter, regulated down to 11" at the kiln.
I have recently fired this kiln to cone 10 in a fully oxidized environment. This type of firing goes quickly, taking about 7 hours.