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Housefull of pots

How did you learn to fire your own kiln?

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Hi folks, 

I am new to this forum and apologise if my questions have been and gone before, I’m sure they have! I have bought an old gas fired port-o-kiln and have had in installed into the granite lean to which has a tin roof,  at the end of the stables (no horses in there anymore) it seems like a good space. Its small but there is air flow. The kiln is small, it has two burners in v good condition and I have a19kg bottle of propane for it. The kiln didn’t come with a flu or hood so I have got someone to fashion a  basic hood and chimney to take the heat and fumes out. There is about an 8” gap between the bottom of the hood and the kiln to use a damper.  I have done a couple of firings with a local potter who has a pretty unconventional approach to firing, and I have learnt alot but I woukd like to give it a gallop and see if I can put into practise what I’ve learnt.  I have found it quite hard finding solid info on gas firing. I will be firing a range of stoneware and porcelain from 1260 -1300 in reduction. The potter who helped me before used gloves and a hire fire brick as a damper, but I am a little worried about forcing the heat in for some reason - I havnt seen many kikns in my time is this ok practise to control the atmosphere? 

Where and how did you learn to fire with gas/wood etc? Can you give me any tips or benchmarks? Any good books you can recommend please? So interested to learn more about firing and different kilns. 

Many thanks for reading! 

Edited by Housefull of pots
Typos

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I learned (and continue to learn) by trial an error.  Your friend controlling the damper with a quick afire brick is an example of how to control the atmosphere in the kiln, adjusting the damper adjusts how much oxygen is pulled into the kiln with the fuel.  If you've watched a few times and feel like you could make it through a firing alone, give it a shot!

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I've fired many kilns that use a brick as a damper. You could also use a kiln shelf if it'll fit where it needs to be.

Most gas firing knowledge is learned from person to person, not from books. The basics are all essentially the same, but each kiln fires differently and will have different pressure, air, and damper settings. Each firing can have different settings, depending on how the kiln is loaded.

It's all about balance between the gas, air and damper. They all work together to provide heat, pressure, and atmosphere. The biggest mistake people make in firing gas kilns is thinking that you're trying to pump in heat and hold it, like you do with an electric kiln, and end up turning of the gas way too high. What you're really doing in a gas kiln is moving hot air through the kiln. The hot air comes in, transfers the heat to the ware (and kiln bricks), and moves out, to be replaced by more hot air. It's more like breathing. Too much gas or air and it bogs down. So you need just enough gas to get the rate of climb you want, enough air to get the atmosphere you want, and the damper set so there's pressure in the kiln. How you achieve all of that depends on the type of kiln and burners you have.

People fire a lot of different ways. I've seen a lot of teachers use firing schedules that waste a ton of gas, because they weren't having to pay for the gas out of their budget. You can also go the opposite way and fire too quickly, which causes some kilns to fire unevenly. There's a rate that your kiln will be happy with, and you'll have to find that. I have a friend with two identical old Alpine kilns that were built at the same time, delivered to his school on the same day, etc. One likes to fire about an hour faster than the other for some reason. Every kiln is unique.

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On 10/14/2018 at 4:14 PM, liambesaw said:

I learned (and continue to learn) by trial an error.  Your friend controlling the damper with a quick afire brick is an example of how to control the atmosphere in the kiln, adjusting the damper adjusts how much oxygen is pulled into the kiln with the fuel.  If you've watched a few times and feel like you could make it through a firing alone, give it a shot!

Hey Liam,

Thanks for your words of wisdom.. I felt pretty good about going for it, I just needed to ask around for some reassurance that I was on the right track. I fired today, lit it up at 9 and finished at 5. Felt prettty relaxed about it, and seemed to go smoothly, guess I'll find out more tomorrow when I get a peek inside!

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On 10/14/2018 at 4:23 PM, neilestrick said:

I've fired many kilns that use a brick as a damper. You could also use a kiln shelf if it'll fit where it needs to be.

Most gas firing knowledge is learned from person to person, not from books. The basics are all essentially the same, but each kiln fires differently and will have different pressure, air, and damper settings. Each firing can have different settings, depending on how the kiln is loaded.

It's all about balance between the gas, air and damper. They all work together to provide heat, pressure, and atmosphere. The biggest mistake people make in firing gas kilns is thinking that you're trying to pump in heat and hold it, like you do with an electric kiln, and end up turning of the gas way too high. What you're really doing in a gas kiln is moving hot air through the kiln. The hot air comes in, transfers the heat to the ware (and kiln bricks), and moves out, to be replaced by more hot air. It's more like breathing. Too much gas or air and it bogs down. So you need just enough gas to get the rate of climb you want, enough air to get the atmosphere you want, and the damper set so there's pressure in the kiln. How you achieve all of that depends on the type of kiln and burners you have.

People fire a lot of different ways. I've seen a lot of teachers use firing schedules that waste a ton of gas, because they weren't having to pay for the gas out of their budget. You can also go the opposite way and fire too quickly, which causes some kilns to fire unevenly. There's a rate that your kiln will be happy with, and you'll have to find that. I have a friend with two identical old Alpine kilns that were built at the same time, delivered to his school on the same day, etc. One likes to fire about an hour faster than the other for some reason. Every kiln is unique.

Hi Neil,

Thanks so much for this. I found your analogies and openness really useful.  I chose a gas kiln because I am an analogue girl, and I kind of think of gas firing a bit like photography, the kiln and the camera being very alike in their unique and magical ways - and much of what you wrote atested to that. I like the use of breathing and the circular movement. Anyway waffle waffle.. I decided to go for it and lit her up at 9 this morning. She is a bit of a galloper being quite small, so had to just keep it as steady as I could. I put it into reduction at 1050 as recommended in my favourite Coopers book of Glazes and kept it in reduction right up to 1250 when it couldn't climb anymore. I opened up the damper and turned the gas down (after tryng to unsuccessfully force it up) and she went up to where I needed it. It was a good lesson for me. Especially in being independent and taking the reins. So helpful to have the support of other potters when learning. THANK YOU!

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@Housefull of potsExcellent! Always nice to hear a success story!

When I reduce, I try to stall the kiln at cone 010 or so for about 45 minutes. It gives the kiln a chance to even out top to bottom, and prevents it from getting too hot and preventing the reduction from penetrating. After that, I shoot for a neutral or slightly reducing atmosphere as it climbs to final temp. With practice you'll figure out how to fire with less and less gas.

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Yayyy!! Well - it may be a disaster! Will have to see. I did want to soak or stall it at 1260 but I lose my nerve a bit when it is roaring and so hot... I tried to keep one burner lit for cool down so it went down slowly but flame kept licking back down through the other burner hole and I just switched off and closed it up. I did hear like splintering noises which made me cringe - do you know what that might be?? Good to hear about your own methods - what do ou mean when you say it prevents the reduction from penetrating? Are you firing above 1300? I think I will struggle to get mine up that far, but maybe it is about switching between oxidation and reduction and give and take on the gas as you described earlier>? 

 

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No Manuel like an electric for gas kilns-since you are a C person you will have to work on the conversions.

I  have fired gas kilns for 45 plus years -you learn by doing

I fire porcelain -I start reducing around 1800 degrees and keep a light  to med reduction until end point on cones-for me thats a cone 11 at 3 o'clock (about 1/2 way down)Then brick it up and push in damper until a few hundred degrees.

My glazes like about 11-12 hour fires for good crystals to form

Good luck

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Portokiln...you in Australia?

Search John Eagle a Victorian potter.

He wrote an article in Pottery in Australia  but now named "the journal of Australian Ceramics" on reduction firing.

He gets beautiful colour variances with reoxidation towards end of firing, blushes instead of the ubiquitous red and gets beautiful colours by Appling washes over the glazes he uses.

You may get insight from this potter on his firing schedules.

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+1 on learn by doing. See what works and do that again.  See what doesn't work and don't do that again/make adjustments to your kiln.  The largest problems I have had with gas kilns I fashioned was stalling them out before target temp because my exit hole(s) were too small. Rather have too large of an exit flue you can close down than one that's "just the right size" based on head scratching. (+1 what Neil said.) Congrats!

Regrading hoods/vents. I've just used HVAC ducting, sheet metal, snips, rivets.  The photo will give you an idea.   Not ideal, but it's cheap and  works to get majority of the hot air out of my 100 year old wooden garage. The metal gets hot enough to screw up the galvanized finish (which is probably toxic by some measure) but that's about it.

IMG_20180729_212722.jpg

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8 minutes ago, Babs said:

500 F or C  F I guess

F, that initial drop is just the heat in the air dispersing, it still takes 8 or so hours to get down to 300 when I crack the lid.  My fiber is 2 inch 8 pound, the outside gets to about 400 degrees during a cone 6 firing (inside is 2250) so it's pretty decent insulation

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I've recently converted an electric kiln to gas.

Today I started firing it with cone packs I made the previous night. I had put holes holes in them, and they seemed pretty dry. Lucking after about an hour I looked in my burner port and saw debris in the bottom of kiln. Both my cone packs had exploded. I had to shut it off, wait until it cooled and brush off clay fragments from all my ware, and repack the whole thing. I've now made a load of cone packs that will be dry well before I need them. 

Last firing I had a load of dinner plates to bisque. I has struggled to get a low enough flame when candling the kiln. And after about 1 minute the rim of one of the plates near the flame path exploded. I pulled the flame back and continued thinking the rest were ok. I will be more careful, and keep large plates away from flames in future.

I had stacked 6 plates in pairs on shelves with sand between them, to save on kiln space. Two plates were on shelves of their own because I was worried this might end badly.  I do stack bowls with sand without problems. When I unloaded the kiln, all the stacked plates were cracked to bits, the plates on their own shelves were fine. So I won't stack plates like that again, I need to buy some more props and shelves. 

This probably doesn't help you at all, but is a reminder to me not to do stupid stuff again. Whatever you do, there will be mistakes. You've just got to learn from them. 

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15 minutes ago, tomhumf said:

I've recently converted an electric kiln to gas.

Today I started firing it with cone packs I made the previous night. I had put holes holes in them, and they seemed pretty dry. Lucking after about an hour I looked in my burner port and saw debris in the bottom of kiln. Both my cone packs had exploded. I had to shut it off, wait until it cooled and brush off clay fragments from all my ware, and repack the whole thing. I've now made a load of cone packs that will be dry well before I need them. 

Last firing I had a load of dinner plates to bisque. I has struggled to get a low enough flame when candling the kiln. And after about 1 minute the rim of one of the plates near the flame path exploded. I pulled the flame back and continued thinking the rest were ok. I will be more careful, and keep large plates away from flames in future.

I had stacked 6 plates in pairs on shelves with sand between them, to save on kiln space. Two plates were on shelves of their own because I was worried this might end badly.  I do stack bowls with sand without problems. When I unloaded the kiln, all the stacked plates were cracked to bits, the plates on their own shelves were fine. So I won't stack plates like that again, I need to buy some more props and shelves. 

This probably doesn't help you at all, but is a reminder to me not to do stupid stuff again. Whatever you do, there will be mistakes. You've just got to learn from them. 

I candle with a small hand torch that's barely on, but there shouldn't be anything directly in the path of the flames, make sure your bag wall is protecting whatveer

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13 minutes ago, Mark C. said:

Make your cone packs many days before needed  in winter and put them on heater or dry in summer sun

The learning curve in ceramics can be brutal

I do mostly make my own cone packs but I have a few made out of sections of soft brick in case I forgot and I have a few of the Kemper wire cone holders for witness cones.  Come in handy when you forgot to make up some packs and it's go time

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1 hour ago, liambesaw said:

I candle with a small hand torch that's barely on, but there shouldn't be anything directly in the path of the flames, make sure your bag wall is protecting whatveer

Hand torch is a great idea, I think I shall get one. I don't have a bag wall, my kiln is tiny and shouldn't really be trying to fire large plates... But I really want to.  It fires pretty good apart from when stuff explodes. 

 

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27 minutes ago, tomhumf said:

Hand torch is a great idea, I think I shall get one. I don't have a bag wall, my kiln is tiny and shouldn't really be trying to fire large plates... But I really want to.  It fires pretty good apart from when stuff explodes. 

 

It's bigger than mine!

 

 

IMG_20181021_152428_crop_411x831.jpg

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Even totally dry pots will have some level of moisture in them, just a few percent. That little bit has to be driven off before the pieces get too hot and the moisture turns to steam. And even then, heating too quickly can cause uneven expansion which causes cracking.

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Yeah, most people know about the mechanical water(water for manipulation), some know about atmospheric water(environmental moisture), but many forget the chemical water(inherent in the clay formula) that has to evaporate out during the firing process. Biggest mistake of naive potters learning to fire.

 

best,

Pres  

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