Friday, July 2, 2010

A Summer Kiln for All Reasons

We've had a couple of cooler days so I took advantage of the break to construct a small, multi purpose gas kiln to use this summer. The air conditioner, in the house, is keeping the electric meter spinning and I don't want to add to the load by using the electric kiln.  I thought you might find it useful to see how I built it. 

This kiln is constructed from a 20 gallon trash can lined with ceramic fiber. You don't want to wrestle with that fiber when you're hot and sweaty.

This is a medium sized kiln built with a 20 gal. trashcan . It will fire a pot that is about 10" wide and up to about 20" tall with room to spare. Most of the jugs I fire are 16" or less and less than 10" wide.I only fire one piece per load so I have time for post firing treatments without worrying about dealing with a second pot that needs immediate attention.. With the addition of a chimney it will fire to at least cone 6 in little more time than it takes to get to Raku temps. The can provides some heat retention and it can be down fired if fast cooling is a problem. With practice it should fire in oxidation or reduction. It is built so the kiln is lifted off the piece. If necessary a reduction container could be placed over the pot and it could be reduced in situ.

The Raku Configuration

The High Fire Config.
The fiber  lined chimney will increase draft in the kiln allowing it to fire to higher temps. Many small kilns stall because they can't exhaust the burned gases efficiently. Most raku burners are capable of much higher temps.

I'm using 1" 8lb density Ceramic fiber rated at 2300f. I cut two circles and made a double thick top. Pre-fired ceramic buttons made from a heavily grogged stoneware are used to secure the fiber to the sides and top of the kiln. Kanthal element wire is used to secure the buttons to the kiln body.

The element wire is  poked through the hole in the tab I made on the back of the buttons and twisted. I like to use tabs as opposed to two holes (like a button), The tabs act as a stop when pulling the wire tight against the side of the kiln.

I pull the wire through a hole (punched with an icepick) then twist it back against the side in a loop. This loop gives some when the heated wire expands. I can adjust the tension with needle nosed pliers as needed. The buttons are easily replaced if broken.

Excess fiber is folded over the bottom and secured with some large clamps hooked together.
Plumbers pipe hanger strapping or wire cable can be used also. I had the clamps handy so that's what I used.

After securing the fiber I sprayed a couple of coats of a Ceramic Fiber Rigidizer with my glaze sprayer. It is blue (Smurf Pee?) when you spray it on but dries and fires clear. It is a Colloidal Silica. Some use a product called ITC. ITC is a fine product but at $38.00 a pint I find it a little spendy compared to Ins Tuff at $39.00 A GALLON. Nothing wrong in using  ITC  but personally I would save it for a more permanent kiln that gets less rough use. Even with the best care raku kilns will need the blanket replaced sooner than later.  You don't have to use a rigidizer at all if you don't want.

The flue hole is made from a heavily grogged thrown stoneware collar. I think it makes a smoother exit for gases and helps to get higher temperatures.

Handles are repositioned from the bottom of the can to the top the kiln and reattached with sheet metal screws. This allows me to lift the kiln off the fired pot.

The removable chimney  is not needed for raku and would be in the way. but it is invaluable for attaining higher temps. The height should be at least as tall as the firing chamber to get good draft. Kilns  must be able to exhaust burned gases efficiently to reach higher temps. A piece of fiber across the top can provide control for reduction and regulate temperature climb. The chimney is made from a 7" diameter 24" tall section of duct work from Lowes ($3.98). It is lined with 1" fiber that was glued in place with sodium silicate giving a 5" diameter chimney. That should be sufficient for such a small kiln. A larger kiln might require larger chimney. I can attach the fiber with buttons but I don't think it will be necessary once it is rigidized.

I use two old kiln shelves for a base. The floor will be covered with a layer of fiber before firing. The firebox is made of insulating firebrick and is stacked dry. This allows some adjustment to fuel/air mixture. I can pry the bricks apart to allow more air if needed. A tight kiln is not necessarily an efficient kiln. The flame travels under the bottom shelf and rises through the kiln. I raise the shelf off of the floor allowing about 6" for combustion.
Tip: Using two pieces of shelf with fiber between helps keep the bottom cooler and makes the kiln fire a bit more even.

This is a standard adjustable propane regulator. The burner is an Air Mixer  that uses 2" pipe for the burner.  Part number FS-125P at Laguna Clay. I have powered large and small kilns with this one since 1972!! The venturi is cast iron but the burner body is pipe that is replaceable.


Until We Bead Again, Beth Murr said...

Great news I fixed my pottery wheel. Rust vs Toothbrush. Toothbrush wins. You can read about it on my blog. Yippee...I'm spinning again! Nice kiln by the way. I have a similar one. See my video on how not to light it. I'm such a beginner but I'm learning!

Wildmud said...

Great save on the wheel. If you're a potter you had better be good at fixing stuff (or have a fat wallet). Hilarious kiln video. A rocket kiln for the 4th of July! I'm adding your blog to my links.

Until We Bead Again, Beth Murr said...

That explosion was quite a shock. My son looked up and asked, "Mom do I have any eyebrows left?" We were very lucky no one was injured. Luckily I am pretty good at fixing things. Especially since my wallet is pretty thin. Thanks for adding my blog.

madpotter said...

Great post and photos! One of the better DIY on raku kiln building that I've seen.

Wildmud said...

Thanks Gary. It looks like Raku Build Tutorial time on the blogs. Ron Mello just posted the build of his elegant kiln on his blog and Paul The Potter just built a "Dustbin Kiln" on his.
I added your blog to my links.