0645: pilots lit door open
0630: pilots upper temp 220 lower 220
0645: pilots upper 384F Lower 557F smell wax bur off
0720: pilots upper 447F Lower 594
0742 pilots upper 549F Lower 656F firing smell
0820 pilots upper 686F Lower 709F Turn on burners 0.5 blue flame
0844 Upper 1007F lower 1322F oxyprobe 0.03 move damper in 1 inch
0900 upper 1144F lower 1457F oxyprobe no reading put piece of fiber over 1/2 of burner port entrance each side to block 2ndary air.
0930 upper 1288F lower 1563F damper in another inch upped gas to 2.0 no oxy readout.
0940: upper 1388F Lower 1716F gas to 5
0945: upper 1521F lower 1985 oxy .08-.09 covered flue 1/2 increased gas to 9
1015: upper 1997 LowerOL switched to C oxy .68 redux smell
1020: upper 1123 C Lower 1378 oxy .68 cones unmelted inside kiln orange.
1030: upper 1150C lower 1405C oxy .62 cones not bent
1047: upper 1199C lower 1361C oxy .26 increased gas to 10
1055 looked at cones saw R shelf had fallen followed by left shortly after.
Turned off kiln allowed to crash cool to touch in about 4 hours.
Monday, June 1, 2009
HOTTER IS NOT ALWAYS BETTER
This past week-end I did my first solo gas firing at my studio. I'd like to provide the particulars about my kiln and firing before I discuss the results and ask for recomendations to help even out the firing.
I have a fiber updraft kiln with 2 venturi propane burners that I had Mark Ward Modify with baso valve pilots. This required that I enlarge the flame port to acomidate the pilots on each burner.From what I read seemedto indicate the holes should have 1/2 to 1"of open space around them which I did. It also said to have the burner 1/2 to 1" away from the entrance to the port to allow for secondary air. This is a cross draft kiln.
The interior measurements are 26 1/4 wide 27 1/2 deep and 34 highnot counting the 12" arch. It was loaded with 3 pairs of 12x24" shelves. I first put in 6 soft bricks 8 1/2" high in the area where the burners were and covered it with 2 shelves, then start to put in mmy pots. I used ^10 B mix laguna and 3 different copper reds, Tom Colemans, June Perry's and David Cuzicks. I got some beautiful copper reds with an oxyprobe reading of .7 after 1200 but the top and bottom of the kiln started with a 200 F difference the bottom being hotter I have included my firing record. I had 2 thermocouples placed in the side of the kiln one in the top are and 1 in the bottom. The oxyprobe was placed in the middle on the other side and found it would read a temp conversion to about 1800 then went OL. AT 1200 the instuctions with the oxy probe said to increase the gas which I initially did slowly from 2 to 5 with 0 reading on the oxyprobe atmosphere.I kept inching the damper closed till it was about 1/2 way ( damper opening is 7 1/2" by 5 1/2" ) waiting about 15 minutes between changes for a reading change. I was then told the instructions said to turn the gas all the way up so I went to 9 and finally got an oxyprobe reading of .7 but the temp difference went from 300 to 500. We started to doubt the validity of the lower temp probe since the kiln looked orange and the only set of visible cones were unmelted. This kiln only hs 1 spy hole so only one set of cones was visible even though I put 3 in. I will correct this for future firings and cut 2 mor holes in the door, so we have a double check point. We continued to fire and the temp increased on the upper thermocouple which we decided to follow but a short while later I looked in the peep for the cones only to see the shelf on the right had dropped and no cones were visible followed shortly by the left stack of shelves falling. At this point I shut the kiln down not bothering to cover the top with a fiber blanket and stuff the ports or fire down as I had planned. The kiln was kool in about 4 hours and when we opened it we had some beautiful copper reds too bacd they were stack together and to the shelves that broke in the middle ion the bottom 2 level. The soft firebrick had started to melt and curve toppling the shelve. Post that dropped from the middle layer and fell to the area under the 1st shelve melted into a puddle.
Since this message won't let me change my mispellings without rewriting the post I appolagize. I also want to say I took a piece of fiber and block paart of the port hole for the burners when I was trying to get reduction before upping the gas.
Any input as to how I can even out the firing would be appreciated and now I know that when the thermcouple read the bottom shelf area was1361C about 2500F it was probably right. I will be posting this on clayart and appreciate folks responding there if possible.
Things learned for the positive. The best reds were applied thicker than my normal glazing. The ones with the mottled look that I like were on the middle shelf were as the top shelf same galze was a bit murky and the bottom shelf mostly burned out. Also you don't need to slow cool to get copper reds ...Liz
I have a fiber updraft kiln with 2 venturi propane burners that I had Mark Ward Modify with baso valve pilots. This required that I enlarge the flame port to acomidate the pilots on each burner.From what I read seemedto indicate the holes should have 1/2 to 1"of open space around them which I did. It also said to have the burner 1/2 to 1" away from the entrance to the port to allow for secondary air. This is a cross draft kiln.
The interior measurements are 26 1/4 wide 27 1/2 deep and 34 highnot counting the 12" arch. It was loaded with 3 pairs of 12x24" shelves. I first put in 6 soft bricks 8 1/2" high in the area where the burners were and covered it with 2 shelves, then start to put in mmy pots. I used ^10 B mix laguna and 3 different copper reds, Tom Colemans, June Perry's and David Cuzicks. I got some beautiful copper reds with an oxyprobe reading of .7 after 1200 but the top and bottom of the kiln started with a 200 F difference the bottom being hotter I have included my firing record. I had 2 thermocouples placed in the side of the kiln one in the top are and 1 in the bottom. The oxyprobe was placed in the middle on the other side and found it would read a temp conversion to about 1800 then went OL. AT 1200 the instuctions with the oxy probe said to increase the gas which I initially did slowly from 2 to 5 with 0 reading on the oxyprobe atmosphere.I kept inching the damper closed till it was about 1/2 way ( damper opening is 7 1/2" by 5 1/2" ) waiting about 15 minutes between changes for a reading change. I was then told the instructions said to turn the gas all the way up so I went to 9 and finally got an oxyprobe reading of .7 but the temp difference went from 300 to 500. We started to doubt the validity of the lower temp probe since the kiln looked orange and the only set of visible cones were unmelted. This kiln only hs 1 spy hole so only one set of cones was visible even though I put 3 in. I will correct this for future firings and cut 2 mor holes in the door, so we have a double check point. We continued to fire and the temp increased on the upper thermocouple which we decided to follow but a short while later I looked in the peep for the cones only to see the shelf on the right had dropped and no cones were visible followed shortly by the left stack of shelves falling. At this point I shut the kiln down not bothering to cover the top with a fiber blanket and stuff the ports or fire down as I had planned. The kiln was kool in about 4 hours and when we opened it we had some beautiful copper reds too bacd they were stack together and to the shelves that broke in the middle ion the bottom 2 level. The soft firebrick had started to melt and curve toppling the shelve. Post that dropped from the middle layer and fell to the area under the 1st shelve melted into a puddle.
Since this message won't let me change my mispellings without rewriting the post I appolagize. I also want to say I took a piece of fiber and block paart of the port hole for the burners when I was trying to get reduction before upping the gas.
Any input as to how I can even out the firing would be appreciated and now I know that when the thermcouple read the bottom shelf area was1361C about 2500F it was probably right. I will be posting this on clayart and appreciate folks responding there if possible.
Things learned for the positive. The best reds were applied thicker than my normal glazing. The ones with the mottled look that I like were on the middle shelf were as the top shelf same galze was a bit murky and the bottom shelf mostly burned out. Also you don't need to slow cool to get copper reds ...Liz
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