Tall Converted Propane Kiln Question

[Callum Donovan-Grujicich]

Hello, I have a bit of an odd question.

I have been considering converting three electric kilns to downdraft gas. I have recently been offered two free small electric kilns, but they are too small for what I want to fire, so I had an idea: would it be possible to stack the two smaller kilns on top of a large kiln and fire the entire thing as one unit? I wanted to use weed burners and propane as the power source, so would it be better to put three weed burners at the bottom of the large kiln, then put one weed burner on each of the smaller kilns? Or would it be better to install the weed burners in a traditional way (all 5 at the bottom of the large kiln)?

Thanks,

Callum

[neilestrick]

4 hours ago, Callum Donovan-Grujicich said:

Hello, I have a bit of an odd question.

I have been considering converting three electric kilns to downdraft gas. I have recently been offered two free small electric kilns, but they are too small for what I want to fire, so I had an idea: would it be possible to stack the two smaller kilns on top of a large kiln and fire the entire thing as one unit? I wanted to use weed burners and propane as the power source, so would it be better to put three weed burners at the bottom of the large kiln, then put one weed burner on each of the smaller kilns? Or would it be better to install the weed burners in a traditional way (all 5 at the bottom of the large kiln)?

Thanks,

Callum

If the rings are the same diameter, then you can stack them.

Just using more weed burners isn't the solution to making a conversion kiln fire better. Gas kilns don't work on the theory that more gas/ flame equals more heat. It's more complicated than that. It's a balance between fuel, air, secondary air, and air flow through the kiln, among other things. How did you decide that 5 weed burners were needed? Weed burners are also the least safe method of firing with gas. There are no safety systems of any kind. No pilot light, no hi temp shutoff, nothing. It's not as simple or as safe as I think you're picturing it to be.

I'm repeating myself here, but IMO this type of kiln is not the best way to fire your sculpture. Large pieces have all sorts of issues that small pieces don't. Porcelain pieces have all sorts of issues that stoneware pieces don't. Compounding all that with a less-than-ideal kiln is just adding to the potential for failure. If you decide that it's the only way to go, then I would strongly consider just firing it to bisque temps. As a sculpture, vitrification isn't required. I'm not saying it won't work, but if you want the best odds you can get, this isn't the way to fire it.

[Callum Donovan-Grujicich]

15 minutes ago, neilestrick said:

If the rings are the same diameter, then you can stack them.

Just using more weed burners isn't the solution to making a conversion kiln fire better. Gas kilns don't work on the theory that more gas/ flame equals more heat. It's more complicated than that. It's a balance between fuel, air, secondary air, and air flow through the kiln, among other things. How did you decide that 5 weed burners were needed? Weed burners are also the least safe method of firing with gas. There are no safety systems of any kind. No pilot light, no hi temp shutoff, nothing. It's not as simple or as safe as I think you're picturing it to be.

I'm repeating myself here, but IMO this type of kiln is not the best way to fire your sculpture. Large pieces have all sorts of issues that small pieces don't. Porcelain pieces have all sorts of issues that stoneware pieces don't. Compounding all that with a less-than-ideal kiln is just adding to the potential for failure. If you decide that it's the only way to go, then I would strongly consider just firing it to bisque temps. As a sculpture, vitrification isn't required. I'm not saying it won't work, but if you want the best odds you can get, this isn't the way to fire it.

I decided I needed 5 weed burners because the two smaller kilns are a size which I have seen use one weed burner each, and the large kiln is larger than the size that usually uses two, so I thought is should use 3. So 5 in total. But this is not the way it works?

I am concerned that if I do not fire to the maximum temperature (cone 6) the sculpture will not be strong enough for my needs. This is because the sculpture is a box, weighing 160 pounds, that needs to be supported by four hollow legs. I worry that if the clay is not fired hot enough, the legs may not be strong enough to support the box. Would firing to a bisque temperature provide enough strength? If not, would firing to a temperature like cone 4 instead of cone 6 be a safe way to fire the sculpture with a minimized potential of collapsing of the clay, but still be strong enough?

I have some cone 4 test pieces, could these possibly serve as a good benchmark for results from the first firing?

p.s., the rings of the small kilns do not line up at all with those of the large kiln. They would basically be stacked on the middle of the lid of the larger kiln.

[Min]

@Callum Donovan-Grujicich

While I totally applaud your creative thinking and open mindedness, firing a sculpture like yours is way more complicated than just getting a kiln up to temperature/cone. Building a Frankenkiln and firing it with 5 weedburners is both extremely dangerous and in my view highly unlikely to be successful in firing what you have described. Porcelain sculptures are difficult to fire in the best of situations. Sounds like you've put a lot of work and thought into it, we want you to have a successful firing. I'ld strongly encourage you to pursue your original plan on paying someone experienced in firing their kilns to fire your work for you. 

[Callum Donovan-Grujicich]

9 minutes ago, Min said:

@Callum Donovan-Grujicich

While I totally applaud your creative thinking and open mindedness, firing a sculpture like yours is way more complicated than just getting a kiln up to temperature/cone. Building a Frankenkiln and firing it with 5 weedburners is both extremely dangerous and in my view highly unlikely to be successful in firing what you have described. Porcelain sculptures are difficult to fire in the best of situations. Sounds like you've put a lot of work and thought into it, we want you to have a successful firing. I'ld strongly encourage you to pursue your original plan on paying someone experienced in firing their kilns to fire your work for you. 

Yes, I would also like to have someone else fire my work. The trouble is that I have contacted about 20 or 30 places, none of which so far have been capable or willing to fire my work.

[Pres]

As Min has said, you are creative, and that is to be considered a plus. At the same time though, I think your plan needs to be thought through more. Min's point about porcelain sculpture is true, as lack of controlled temperature rise at different points in the firing can cause things to either blow up in early stages or in later stages warp. Also of concern here should be cool down which could cause problems with cooling dunts. 

There are a great many books out there on building kilns, use of space age materials, and firing sculpture. Many of these were written in the 70's and updated over the years, but the mechanics and theory of burner use and heat rise still stand. Please research further before stepping into a project that could end up hurting yourself or others.

If you find someone to fire your sculptures, would it not be of benefit to see if you could help with the firing, or use him as a mentor? I would think that that would be a win/win for you and much safer.

 

 

best,

Pres

[Mark C.]

I'm pretty sure (I have some experience in ceramics) that you can not control the early part of firing with a weed burner . This means you will most likely blow up that 160# sculpture. The key with something like this is the slow early stages of firing-like I said before it should take days not hours. It does not. matter how dry you think it is. 160#s of clay needds a really slow candle period.An electric kiln can do this better than any gas kiln unless you are a very experienced gas kiln person who knows how to go very slow and uses a digital meter.

We are just trying to guide you into a better outcome than blowing or cracking your piece up.

I would keep trying to find a firing source with knowledge.

[Callum Donovan-Grujicich]

Thank you all for your replies. I will definitely keep trying to find someone who will fire my sculpture.

[liambesaw]

Learning to gas fire in a makeshift kiln while trying to not destroy a sculpture is going to be very, very difficult. 

My first gas firing in a makeshift kiln was to cone 04 and it took 14 hours and 40 pounds of propane.  It was a nightmare.  

I did a lot of research and ended up with a similar design, but it could reach cone 10 easily with some tweaks.  But it took 2 years and several dozen firings to get to that point.

 

 

 

 

[Callum Donovan-Grujicich]

Update: I just found a place with a large gas kiln that will fire my work.

[Mark C.]

Yay