Unusual question on pottery

[4dead]

My wife is getting into making small pottery tiles and has no kiln. I told her we could put them in my coal forge and try that. She says they only need to fire at 1700 and a coal forge gets 3500. Anyone have any suggestions on how we can try this? Thanks Randy.

[FredW]

Why not build a kiln. Use wood for fuel. If you can enclose the forge good enough to hold the heat should work. Do a search for wood fired kilns or home built kilns. May give you some ideas. There is lots of info on it out there.

 

 

Also do a search for sawdust kiln. I saw one on you tube that was very simple to build. could also do pit firing which essentially a pit with a lid on it, tin or whatever that wont burn, and small openings in opposing ends to create airflow. Just put in pottery, or tiles, then surround it with wood, sticks, leaves, etc. and light one end.

 

Fred

[mailledemon]

The forge heats up too quickly if you just throw the tile in there. if you make a little kiln out of firebrick with slots in the floor, you could set that on the forge and fire the tiles. It'll take a couple hours to fire the tiles so if you want to put some steel under the kiln to work you can. I use one of these occasionally for some wheel pots i make.


I used to do some pottery.

[4dead]

We tried a 55 gal. drum with a roaring fire last weekend. Did not get hot enough to harden the tiles. Thanks Randy.

[EtownAndrew]

From having already gone somewhat down this road my suggestion is to spend $100 and buy a used electric kiln off Craigs list. I ended up spending more and having a lot of trial and error trying to make something work myself using my propane forge burner. As someone else already mentioned I struggled with heating up the clay too fast and cracking. Also some kilns will include a "candling" warmer temp setting that will hold the clay at less that the temp of boiling water overnight prior to the regular firing and allow the clay to release any remaining water. If you heat up too fast the steam can pop off the glaze in spots and mar the glaze if you don't end up also cracking. I did ultimately create a 16" cube interior brick kiln that worked.

 

I'm impressed that one of the above posters was able to set a small kiln over his coal forge and fire a pot.

[Jacques]

The only pottery technique that I am aware of that will (probably) work in a forge type experiment is Raku, and that finish is rather rough.

 

If you want to make nice smooth looking stuff electric is the way to go.

[evfreek]

All a forge is good for is testing clay samples for firing.  I had a similar problem to you.  But in my case, I needed to test a clay sample to see if it matured properly.  I made several trial pieces and warmed them up in an annealing oven.  Many of them shattered when the water boiled out.  You have to go really slow at this point.  One of the survivors was then tossed into the gas forge.  The end nearest the flame was overfired.  The end near the opening was underfired (chalky).  The part in the middle was just right.  I then was able to commit a full load for bisque firing and I had a 100% success rate in the electric kiln.

 

After learning from this experiment, it was time for a little web surfing.  The information is out there if you look.  Raku only survives because of the design and the clay mix.  Use thin walls, perfect construction, and heavily grogged clay.  Even then, expect some failures.  Also, 1700 is a little low for maturing the clay.  This ware will not be food safe.

 

You are well ahead of the general public when it comes to experimental kiln construction.  My suggestion is to build a quickie Raku trashcan kiln, and traverse the two critical temperature points carefully (de-water and quartz transition).  Learn the concept of candling.  Also, do not let your flame go out during the early warmup stage.  This provides unique hazards, unlike those faced by blacksmiths.  Learn about "purple peepers".  Be very careful about leaving the homemade kiln unattended during the initial ramp-up.  Don't just say OK, OK and wing it.

[Gazz]

I tried to fire some small clay pieces in my gas forge a few years ago.   The clay did not like it and all the pieces cracked.  I tried bringing the heat up slowly and cooling them down slowy as well as it would be done in a gas kiln for pottery.  I also tried to fire them in what potters call a sager which is just a larger vessel that the object you are trying to fire fits into.  It helps to moderate heating and cooling and the atmosphere which can greatly affect the colors of the glaze.  Talk to a local potter, they may let you add the pieces to their kiln for a small fee, or buy an electric.

Raku firing is fun as you get to mess with the hot pieces right out of the kiln - lots of smoke and fire.  The pieces are essentially decorative though since they do not get hot enough in the kiln to vitrify completely and the clay is a bit pourus

[Bentiron1946]

I have made several burnout ovens(kilns) over the years for my bronze casting that have use natural gas or propane as a fuel. The first one used ordinary fire place fire brick and I sold it to a potter and he loved that thing. It could get up to 2,200F but was much easier to control to just about any temperature you wanted because I had four rows of burners under it. For my burnouts I would light off the two rows with four burners each and this would melt out the wax and start taking the water out. The potter I sold it to would use this as his first firing step. My next step would be when I removed the pan of melted wax so I could reuse it and then fire off the other two rows of six burners with these I could get a steady 1500F for 24 hours to eliminate all traces of wax and the potter would use this for his final firing temp for his works of art. My burn out oven was made out of angle steel to support the fire brick, burners and a 24" square tile for the bottom where I stacked my flasks and the potter his works. You can buy this bottom tile at pottery supply store along with atmospheric burner, my burners were not atmospheric but more like one would find in a furnace, I cast them myself. I have used loose stacked fire brick and ceramic fiber lined 33 garbage cans, similar to raku, with a single propane burner but didn't like the burnout results as much, here I guess potters aren't as picky as founders but it did in a pinch.

[BIGGUNDOCTOR]

I picked up a nice Cress kiln off Craigslist awhile back for $100. There are lots of used kilns out there.