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Anders

Kiln Opening Temp

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Hey Ceramiacs

 

I've been reading about the topic on the net, and it seems that there are very different opinions on subject. 

I was wondering if someone had a more scientific approach to the matter. 

 

Some say that you should open at 130F, and I think that is a little strange because that means that if you make a cup,

 you have to mind the temperature of you coffee, and other hot things you may consume of you pottery.

 

If you open the kiln at 150f and hear crackling, isn't that a coincidence. I mean if the kiln are outside and it is freezing, I see how it might play a role.

But it just seem strange that ceramics that reach red hot temperatures are sensitive too degrees that low .

 

thanks,-] AC

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I think the care is taken for two things ... The pots and the kiln elements ... Neither like being shocked by colder air.

I have been taught it is usually considered safe to open a kiln once the temp drops below 200 F .... Bearing in mind the bottom might be hotter as it holds the heat. If your pots ping then... well they were going to ping later too.

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I have developed a method I like to use for opening a kiln to even temp.

 

I cut off my vent when kiln cuts off at cone 6. Let it cool naturally to 250. Once it reaches 250. I turn on my vent and remove the 2 peepholes. It cools the rest of the kiln pretty quickly and within an hour it is below 150 usually. I like this method because it is evenly cooling. There isn't a huge gust of air coming into the kiln from just yanking pots out.

 

It is also nice and easy to handle with some basic gloves. I used to open at 250, which is what most people do, but I found that the bottom of the kiln was still rather hot, so I developed this method of cooling. It works for me pretty well. Waiting on the kiln to cool below 250 naturally can take like a long time to hit 150s.

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For glaze loads, I like to wait until the kiln is around 100F.  The thermocouple readings are of the air temperature in the kiln; your wares and shelves are likely hotter than that reading.  My thermocouple have a protective sheath; so, they have an adjustment in the controller to compensate for that as they are not reading the actual inside temperature and the offset helps prevent over-firing.  And, for the most part, I'm over the "Christmas" rush of every kiln firing  -- mostly because my kiln is electric and I've settled on a smaller palette of glazes that are consistent in firing.  Letting the kiln cool a bit longer is no big deal. 

 

If you induce pinging by opening the kiln when it was too hot and allowing a rush of cold air . . . that does not mean the glaze would have pinged if it had been allowed to cool further before opening.  Some glazes will ping regardless.  Some pinging can be from operator error. 

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  And, for the most part, I'm over the "Christmas" rush of every kiln firing  -- mostly because my kiln is electric and I've settled on a smaller palette of glazes 

I've decided I'm a Christmas rush junkie.  I find something I like and works and then I'm on to the next experiment.

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We crack the lid on our kiln at 300F and 150F we open it up.

 

We will put gloves on and start pulling items out around that temp. 

 

We throw stoneware.   Our stoneware is micro/dishwasher safe and can be used in the oven.    if your items are designed to be used in the oven (bake ware)  then they should be able to be removed from the kiln at 300+.

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When thinking about oven ware, remember: a casserole removed from the oven at 325F and filled with mac 'n cheese (or your favorite dish) will cool much slower than an empty casserole removed from the kiln at the same/near temperature. What is most important is having a good clay body and glaze fit . . . where both expand/contract together with heating and cooling -- whether in the kiln or in the oven.

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If there's no rush to get the pots out just let the kiln cool naturally to room temp. What the point in spending all the time and energy creating/finishing/firing/etc, to rush a cooling only to damage wares/elements/furniture just to save a couple of hours.

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My kiln is in our garage. So it depends on the season. Right now, being so cold out, I wait til it gets down to 100* than open it and unload it. In the summer when it's really hot out there, I'll prop the lid and pull out the peepholes around 300*.

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for the bisque electric kilns we raise the lid about an inch when it reaches 200. after that, it gets unloaded when its cool enough to unload without gloves. for the gas highfire glaze kilns, they fire friday, unload monday morning so anyone who wants to be there can see the load as it comes out. . as a group studio we kind of have to have a schedule since there is work of many people in each load including kids stuff.  rakuku

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I'm new to using a kiln. How do you vent the kiln? Mine is a blue diamond and no booklet to tell me how. I've tried to find info online with no luck. During bisque, I left the top peep hole open and had a successful firing. Cone05 was successful as well...all peeps closed. Just finished cone6 last night and am waiting for cool down. Was planning to wait til fully cool as I don't have a thermometer to tell the temp. With cone05 I opened a peep, checked by sticking paper in the hole and didn't singe/catch fire, so propped lid to get cool. Can I do that with cone6?

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Where is your kiln located? Basement, garage? How big is the kiln? If it's a small kiln, you may be able to vent the fumes from the space just by putting a fan in a nearby window. Otherwise you'll want to invest in a downdraft kiln vent. If you also want to vent excess heat, then you should consider an overhead hood from Vent-A-Kiln.

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If you're not venting the kiln directly with either a downdraft vent or an overhead hood, I wouldn't leave the car in the garage while firing, and at the very least I would have a fan blowing out a nearby window and a source of fresh air coming in. If you're in a warm area, leave the garage door open some and a fan to move air. A downdraft vent will not only keep the air in the garage cleaner, your glazes will look better and your elements will last longer.

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1 hour ago, Marie Lindahl said:

I don't keep the van in the garage while firing. Nothing else is in the garage...22x26 sq ft. with my studio space being 9x13 inside the garage. Kiln is around the corner from,there. I'm in IL so its 32 degrees right now.

Knowing that you likely could benefit from a down draft vent installed on your kiln to minimize the burn off fumes in the garage, house and ensure decent oxidation firing.

No more fiddling with port plugs after that.

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whenever you can touch the kiln without feeling heat will  indicate the temperature you can remove the work.   kiln gloves allow me to lift out shelves when their temp is above comfort level for skin touching.   if you can feel heat rising around the shelves, it is too hot for your hands even with gloves.  the pots might not suffer but you could.

 

 

Edited by oldlady

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42 minutes ago, Marie Lindahl said:

Port plugs??? The garage is detached. 10ft from house

 

Ok, less fumes in the garage, better oxidation if you go with down draft vent, leave the port/ sight/ peep holes covered. Detached garage means you probably have an alley or a long driveway to shovel. 
Grew up in Chicago, typical brick bungalow and detached single car garage.

It appeared to me your studio is in the garage along with the kiln to which a down daft vent would at least remove most of the dangerous fumes.

Edited by Bill Kielb

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I only use my electric kiln for bisque, so I unload as hot as possible, usually around 200 with gloves.  I want to get some work out of the remaining heat by loading at least some of the bigger pots for the next load.  With the kiln closed back up and a fiber blanket on top, it will stay well above room temperature for the rest of the day helping to dry some doubtful pots.

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