"Burping Kilns" - An Experiment.

[Brandon Franks]

Hello,

 

I finally feel comfortable with the number of tests I have run to share this information and make a definitive conclusion and recommendation. 

 

I have run 34 firing tests with burping and contrasted the results with 28 firings without burping.

 

THIS IS ONLY A PROCESS FOR GLAZING. DOING THIS FOR BISQUE MAY CAUSE CRACKS. I HAVE NOT TESTED ON ONCE-FIRED WORK.

 

Firstly, what do I mean when saying "burping kilns."

The term comes from Raku (where I got started with pottery). Burping Raku is when you let oxygen into the container/ditch that you have your raku pieces sitting, many other potters, and I have found it to allow the glazes to become more active and colorful.

 

However, that is not what I am referring to here.

 

I am going to share with you my process to have your ceramics be more resistant to crawling.

 

Process:

Firstly, I do a slow ramp of my glaze loads (100-150 degrees/hour) to 250 degrees to allow for moisture to leave the pots. However, this is not a slow enough ramp and high enough temperature to completely rid your pieces of water and holding at such a low temperature adds unnecessary time to firings. So, every 150-200 degrees until about 700 degrees, I pop open the lid of my kiln for ten-fifteen seconds to allow for moisture to be released. Now, you are surely asking, "Why?" and "Will this damage my elements?"

 

Why? - When I have burped the kiln, I have found glazes less likely to crawl. I also have found it less likely for the melt on glazes to be uneven.

 

Will this damage your elements? - From what I have found, I have seen no stress on the elements. I have measured the time of firings and the life of the elements over two different sets, testing between burping and no burping. 

 

The process is incredibly easy-

Know your ramp speeds, and calculate when your kiln will progress every 150 or 200 degrees, and go to your kiln with a pair of gloves and open the lid quickly. Do as many times as you would like until you hit 650/700 degrees. Anything over 700 will not work. 

 

(Little side note- If you wear glasses, take them off before doing this. It is incredibly foggy and can probably melt the plastic) 

 

Please try this on your own and let me know if you find this process to work for you and your glazes.

 

  To my knowledge, no one has written about this, and I have come up with this process myself. If this is a process that someone has written about, please let me know, for I do not want to take credit for something that isn't mine, even something as minuscule as opening the lid of your kiln. 

 

 

[liambesaw]

I fire with the peeps out, others have a vent, does this do something these won't do?

[Brandon Franks]

36 minutes ago, liambesaw said:

I fire with the peeps out, others have a vent, does this do something these won't do?

My kiln requires the top peep to be out the entire firing for the fan to work. The fan and the peep don't actually release that much moisture.

 

I find this super effective. If you try it, you will see the amount of moisture in the kiln - way more than I ever thought.

[Mark C.]

I just leave a wedged shaped soft brick under kiln lid leaving it open a bit-You would call this a full burp until around 800-1000 degrees or whenever I go take a look and close it.Kiln is outside in a huge covered area thats closed on 2 and 1/2 sides.My last elements lasted 25-30 years almost. The new ones have two fires on them now as they got replaced two weeks ago.

I'm a little fuzzy on why this may affect the glaze fire in terms of crawling glazes. Is the thgought its weeping out of pots so fast its making for cracks in glaze??In my downdraft I load 35 cubic feet of just dipped  galzed pots that art very wet and have zero crawling issues from fast firing as I also do not baby the 1st or any parts of the fire. A few glazes can be prone to crawling  no matter what you do but I tend to avoid them altogether . Of course I never wash the bisque ware as many do so they only gain water from the wet glaze.In a downdraft water vapor has to go thru the load to get up the stack and usually it just burns  off pretty quickly .I tend to follow the Lou Nils thought of firing as fast as the wares and furniture can take myself in my gas kilns.Whats the downside of that moisture  as its gone as the tem goes up?? You feel that crawling was a issue and is not anymore?I am wondering on the thought? I do not have a fan or leave spy plugs out. Been doing this about 45 years now but only with bisque ware as I fire in a gas kiln much hotter than my electric wants to go at cone 11.

 

[Brandon Franks]

2 minutes ago, Mark C. said:

I just leave a wedged shaped soft brick under kiln lid leaving it open a bit-You would call this a full burp until around 800-1000 degrees or whenever I go take a look and close it.Kiln is outside in a huge covered area thats closed on 2 and 1/2 sides.My last elements lasted 25-30 years almost. The new ones have two fires on them now as they got replaced two weeks ago.

I'm a little fuzzy on why this may affect the glaze fire in terms of crawling glazes. Is the thgought its weeping out of pots so fast its making for cracks in glaze??In my downdraft I load 35 cubic feet of just dipped  galzed pots that art very wet and have zero crawling issues from fast firing as I also do not baby the 1st or any parts of the fire. A few glazes can be prone to crawling  no matter what you do but I tend to avoid them altogether . Of course I never wash the bisque ware as many do so they only gain water from the wet glaze.In a downdraft water vapor has to go thru the load to get up the stack and usually it just burns  off pretty quickly .I tend to follow the Lou Nils thought of firing as fast as the wares and furniture can take myself in my gas kilns.Whats the downside of that moisture  as its gone as the tem goes up?? You feel that crawling was a issue and is not anymore?I am wondering on the thought? I do not have a fan or leave spy plugs out. Been doing this about 45 years now but only with bisque ware as I fire in a gas kiln much hotter than my electric wants to go at cone 11.

 

Many of my (crystalline) glaze books have said something like this and I find it to be fairly true:

"... crawling can be caused by many factors, but for crystalline, it is often because of the moisture in the glaze is leaving at a slower rate then expansion of the glaze"

(that is an excerpt of a text from a friend of mine who has been doing pottery for about 40 years)

 

I have only experienced crawling a few times, but I have found when you rid the atmosphere of excess moisture, it helps prevent the glaze from shrinking rapidly when it hits 1000^f or so.

 

Again, that is my assumption of why it works, I am sure as hell not sticking my head in there at 900^f to watch, but I could very well be wrong about why it helps. 

(attached is a picture of what I am referring to when I say cracks and flaking in glaze, this is from a firing with the burping, end result is the next file, as you can see, no noticeable cracks or blemishes in the melt of the glaze)

I have a lot of results like this, some worse cracking than the others. The picture of the raw glaze was taken around 600^f. 

 

One thing with the soft brick, I have found firings to be A. a bit longer and B. more expensive, it's what made me think of a new way to do it.

[neilestrick]

@Brandon Franks What type of vent are you using on your kiln?

I'm not sure this necessarily translates to all glazes. I think this is specific to crystalline glazes, which tend to have little to no clay in them. If this works for your glazes, that's great and I'm glad you found a way to solve a problem you've been having, but I think that with most non-crystalline glazes, crawling comes from other issues- usually application problems when layering glazes, or from too much clay in the recipe. I think the result is the same, that the glaze is losing its bond with the clay before melting, but the reason it happens is different.

Have you tried just doing a 30 minute hold at 250F to dry out the pots? That should be more than enough to drive off any remaining water if the pots were allowed to dry overnight after glazing.

I would be far more concerned about harming the pots when opening the kiln at 600F than with harming the elements, especially those at the top of the kiln.

[Mark C.]

OK the no clay in the glaze makes some sense as that glaze really wants to jump off a pot. I think a long hold just above water vapor point of 212  degrees (boiling point of water)Like Neil says ar 250 may do the same thing-you could have the lid cracked as well to that temp.. My save the burping deal?

I have some friends who make thier living with crystalline glazes fired high fire in gas kilns-I'll ask them about this.

[glazenerd]

Neil/ Mark:

the 24-28-% zinc content in the recipe causes that.

[Brandon Franks]

6 hours ago, neilestrick said:

@Brandon Franks What type of vent are you using on your kiln?

I'm not sure this necessarily translates to all glazes. I think this is specific to crystalline glazes, which tend to have little to no clay in them. If this works for your glazes, that's great and I'm glad you found a way to solve a problem you've been having, but I think that with most non-crystalline glazes, crawling comes from other issues- usually application problems when layering glazes, or from too much clay in the recipe. I think the result is the same, that the glaze is losing its bond with the clay before melting, but the reason it happens is different.

Have you tried just doing a 30 minute hold at 250F to dry out the pots? That should be more than enough to drive off any remaining water if the pots were allowed to dry overnight after glazing.

I would be far more concerned about harming the pots when opening the kiln at 600F than with harming the elements, especially those at the top of the kiln.

I use a bailey vent, I don't exactly know the science behind it, but you leave one peep open and it sucks from the side of the kiln.

 

Your point about harming the pots was one of my concern, but I have never had any cracks/damaged ware when doing this. I have found it to work with cone 6 glazes too, but have never had any crawling with them.

 

The point of the experiment originally was to find a way to fire my kiln faster and still get the same results. I have found it to help more with the cracking in glazes then actual crawling itself. It works for me, and I shared it with one friend who does cobalt decorated porcelain and she explained that sometimes she would find that glaze cracks or is absorbed more into her cobalt decorated areas (high concentration of kaolin in those ares) more then the clay itself, and she thinks this has helped the issue a bit.

 

Again, this is something that has worked for me, I have no idea why/how it works, but my experiments lead me to believe it does. 

 

[Brandon Franks]

2 minutes ago, Brandon Franks said:

I use a bailey vent, I don't exactly know the science behind it, but you leave one peep open and it sucks from the side of the kiln.

 

Your point about harming the pots was one of my concern, but I have never had any cracks/damaged ware when doing this. I have found it to work with cone 6 glazes too, but have never had any crawling with them.

 

The point of the experiment originally was to find a way to fire my kiln faster and still get the same results. I have found it to help more with the cracking in glazes then actual crawling itself. It works for me, and I shared it with one friend who does cobalt decorated porcelain and she explained that sometimes she would find that glaze cracks or is absorbed more into her cobalt decorated areas (high concentration of kaolin in those ares) more then the clay itself, and she thinks this has helped the issue a bit.

 

Again, this is something that has worked for me, I have no idea why/how it works, but my experiments lead me to believe it does. 

 

Doing this saves me about an hour and a half of firing time and ~30 cents a firing (according to my kiln)

 

 

[neilestrick]

2 minutes ago, Brandon Franks said:

I use a bailey vent, I don't exactly know the science behind it, but you leave one peep open and it sucks from the side of the kiln.

 

Interesting. In every other brand of vent I've seen, leaving a peep open is too large a hole and actually spoils the draft since most peep holes are considerably larger than the two or three 1/4" holes that the vent pulls through. Skutt and Orton both say to use the same size and number of holes for intake, L&L says that most kilns are drafty enough without any holes open since the lid tends to lift a bit as the kiln heats up. Do you find that your Bailey does a good job of venting fumes?

[Brandon Franks]

2 minutes ago, neilestrick said:

Interesting. In every other brand of vent I've seen, leaving a peep open is too large a hole and actually spoils the draft since most peep holes are considerably larger than the two or three 1/4" holes that the vent pulls through. Skutt and Orton both say to use the same size and number of holes for intake, L&L says that most kilns are drafty enough without any holes open since the lid tends to lift a bit as the kiln heats up. Do you find that your Bailey does a good job of venting fumes?

I have never smelled any fumes, but I don't really know. 

 

Judging by the amount of moisture that leaves my kiln, I would say it doesn't do a great job, but it gets the job done.

 

(*attached is the image from their website*)

 

https://www.baileypottery.com/m-405-010.html

 

[neilestrick]

@Brandon Franks What size hole is in the side of your kiln where the hose mounts? It would be interesting to try plugging half the peep hole and see if it does a better job of removing the moisture from the kiln.

[Brandon Franks]

On 1/26/2020 at 8:39 PM, neilestrick said:

@Brandon Franks What size hole is in the side of your kiln where the hose mounts? It would be interesting to try plugging half the peep hole and see if it does a better job of removing the moisture from the kiln.

it is like 3/8ths of an inch- incredibly small.

[neilestrick]

1 hour ago, Brandon Franks said:

it is like 3/8ths of an inch- incredibly small.

Your peep hole is a lot bigger than that, and could actually be spoiling the draft. Try running a firing with all the peeps plugged and see if that makes any difference in the moisture levels. If, by 800 degrees, it doesn't seem to be any different, go ahead and open the peep back up.