How can I tell if my items are dry enough to bisque fire?

[BBceramics]

Hello all! New here today! TOTALLY NEW TO FIRING- so please make fun of me, I don't know what I'm doing lol.  I have been throwing on/off for a number of years and have inherited an old Duncan EA-122 kiln recently (I call it my little grandma kiln). I have never attempted my own firing before but have been doing tons of research to figure out how to do it. The two batches I've tried to bisque so far have both exploded. I have learned this is because they were too wet. They both seemed TOTALLY dry to me. The first item was an orchid pot with a built in tray and had been trimmed and sitting on the shelf for nearly 2 weeks before I tried to fire it. Exploded. One other item in the kiln did not explode how ever the only shelf I had did break (04 kiln sitter). The next was a ramen bowl which was different clay (dries much faster) and had been done and sitting out for 4 days. I was worried about the moisture so put it in my oven at 190 degrees' for 30min or so. It also exploded (04 kiln sitter).   I currently have a third attempt running right now with an 06 sitter. This bowl which was also finished 4 days ago I put in the warm kiln from the previous fire for several hours before turning it on. I have never had anything explode at the studio I fire at but they also use big electric kilns with fancy programming boxes. Mine is just a kiln sitter with a back up timer.  One day I would love a new kiln but for now- I'm trying to figure out how to make my grandma kiln work. Any advice would be appreciated!! 

[Min]

Hi BBceramics and welcome to the forum! 

A simple way to check if a pot still has enough moisture in it to possibly explode in the kiln is to put the bottom of a room temperature pot it against your cheek; if it feels cool then it's too wet to fire as is.

Candling is running the kiln at a very low temperature to ensure the clay is thoroughly dry, how long you candle the kiln for depends on both the thickness and dampness of the pots. To candle with a manual kiln use the lowest setting you have on the switch (if you have more than one switch just use the bottom one). Leave the peephole plugs out, leave the lid propped up an inch or so and let it run. For pots with a wall thickness under about 3/8"  candle for a few hours then continue with the firing. If the pots are really thick and damp then let it candle overnight. (and reset the timer when you go to bisque fire) Close the lid and put a piece of glass over the peephole, if you see moisture on it the pots are still too wet to fire. How fast are you turning up the switches for your bisque?

[Bill Kielb]

I am thinking more likely that your initial firing rate is high and perhaps your wares are thick. Pictures would help of some of the offending pieces. Drying things out below the boiling point is usually key and doing that slowly is even more key. Most find it sufficient to leave their wares just below 200 degrees for Several hours does the trick and in a bisque firing we tend to not exceed 200 degrees per hour, so likely a 12 hour firing.

Folks with manual kilns develop techniques in bisque firings to slow things down. Maybe prop the lid and turn on low for two hours..... then close the lid for two hours, etc..... it’s something they perfect for their kiln.

[Hulk]

I run up to 200F the night before - doesn't take long - shut down, then fire full on the next day.

[BBceramics]

Thank you for your responses! So my grandma kiln has no temp settings or way to control how fast it gets hot. I simply set a certain cone under the sitter and push an on button.  I really have no control on candling or temp ramping. But you guys have already given me some great ideas for things to try before closing the lid and letting it go.  I'll try propping the lid open for a time or setting the back-up timer for an hour or 2 so it shuts off before the cone bends.  The bisque fire I had running last night successfully did not explode! (Once I transfer pictures from my phone to computer I can add some, I am photo documenting all this =) 

Thank you! 

[Dick White]

Some have placed their damp ware in the kitchen oven, set to as low as possible (around 175F) until completely dry. Then transfer to the kiln and fire.

 

[neilestrick]

Yeah, full blast is too fast for all but the very thinnest pots, and even then it would be iffy. It's hard to deal with a kiln like that. Run it for a while with the lid open for a preheat, then slowly close it over an hour or two. Just make sure there is nothing flammable near the kiln while it's open.

[CactusPots]

Bottom line, though, is that every potter here has blown up pots bisque firing.

Wisdom comes from experience, experience from bad choices.