A home-made ceramics kiln from an oil drum has lasted nine years without trouble
By Stephen Wealthall
Nothing vertical beats the excitement of opening a kiln and seeing the effect of naked ﬂame on your creations. Gas kilns produce glaze ﬁnishes that are often unexpectedly beautiful but commercial gas kilns are usually expensive and bulky.
With some bought essentials, a cylinder of gas and a couple of weekends work you can make a kiln that will do initial (bisque or biscuit), glaze and raku ﬁrings and accommodate work of dimensions up to 700 mm high and 400 mm wide.
The chamber is a 40-gallon oil drum lined with ceramic ﬁbre held in place by nichrome wire. Second-hand drum recyclers now talk only in litres but refer to drums as “equivalent to 40 gallons.” To ﬁt on the octagon of ﬁrebricks, the drum should be approx 550 mm diameter. The drum I used is approximately 880 mm high and stainless steel (not essential, but substantial). The ﬁrebox is made of two cut kiln shelves surrounded by ﬁrebricks. One burner gives a temperature of approximately 1060º C and two around 1200º C. I have found that a hired 45 kg propane gas cylinder lasts 4-10 ﬁrings depending on temperature and time. The draught is regulated by pushing a piece of kiln shelf over a 150 mm ﬂue hole.
The drum is raised by a pulley and winch for loading. This arrangement also allows easy unloading for raku ﬁring, where the red-hot work is pulled from the kiln with tongs and placed in metal buckets containing leaves or sawdust to produce startling metallic ﬁnishes.
Temperature from a cheap thermocouple displays on a $10 multimeter.
Cut out the drum end which has the bunghole by running a cutter around inside the rim.
This open end will be the bottom of the kiln. In the centre of the other end that will be the top, cut a 150 mm diameter hole for the ﬂue. To make a ﬂue liner, use a strip of thin steel curved into a circle, notched and bent. Pop rivet or bolt the ﬂue liner into the ﬂue hole.
Around the rim of the top, drill three holes at 120 degrees apart from each other for attaching the shackles of the haul-up system. About halfway up the drum side, drill a 10 mm hole for the thermocouple. For holes to insert wires through to secure the lining, drill ﬁve columns of ﬁve rows of 3 mm holes in vertical lines around the drum and ﬁve holes radially in the top, halfway out from the ﬂue.
Where you are going to place the ﬁrebox, position a beam at least 2.3 metres above the ground.
To this beam, securely attach a pulley for the wire that will raise and lower the kiln. I used old steel-wire rope from yacht rigging, strong enough to hold the weight of the drum, and a small second-hand winch of the type that hauls dinghies onto trailers. Note: Ensure the winch ratchet is really safe before loading or unloading. Level a site under-neath.
To create the ﬁrebox, cut off the corners of the large kiln shelf be-tween marks made at 130 mm in from each corner. This creates an octagon-shaped shelf. Push a ﬁre-brick on edge against each of the four sides that have just been cut. The bricks should overlap by an equal distance at each end of the shelf side. Sit another four bricks on top of the lower bricks to bridge the lower bricks from corner to corner.
On the bottom of the top bricks, mark round where the brick corners sit. Square down the lines then cut the interlock shapes with a hacksaw. Check that the bricks interlock and butt snugly against the base kiln shelf (whole bricks on the long sides of the shelf) and then hole-saw or ﬁle one or two oblique burner holes in one or two of the whole bricks.
To line the drum, you will need to wire the ceramic ﬁbre blanket on with “buttons.”
From the remaining ﬁrebricks, hacksaw 30 “buttons” 10 mm thick and 20 mm wide and drill two 3 mm holes spaced 10 mm apart in the centre of each. Unless your wrists drag on the ground you will need help to ﬁt the ﬁbre blanket.
Cut a blanket length slightly larger than the inside circumference of the drum. Starting at the top, push in the ﬁbre. The standard 610 mm-wide blanket will cover about 70 percent of the drum height in the ﬁrst wrap. Now have the helper push uncut nichrome wire through the previously drilled holes in the drum and through the ceramic ﬁbre, starting at the top.
From the inside, thread a button onto the wire. Using two pairs of pliers, bend a short “U” in the slack wire so it will ﬁt into the second hole of the button. Using needle-nose pliers, the helper outside then pulls the wire tight and bends it into an “L” to retain the wire tightly against the outside of the drum.
Cut off the excess wire. Cut a second cylinder of ﬁbre from the blanket and butt this ﬁrmly against the ﬁrst. Overlap the blanket over the bottom edge of the drum by about 50 mm so that when the end of the ﬁbre blanket is notched (use a craft knife) and ﬂared outwards, the weight of the drum squashes it against the ﬁre-bricks to make a tight seal.
Repeat the exercise with the wire, ﬁxing this second section of the blanket inside the drum. Cut leftover kiln ﬁbre to ﬁt into the top of the drum so it is tight against the ﬂue and the vertical ﬁbre walls.
Secure the drum-top lining with nichrome wire.
Where the ﬁrebox will sit, excavate the soil down 75 mm, tamp and level and ﬁll the hollow to 25 mm deep with sand.
Leftover ﬁbre can be used as an insulating base by making an octagon (base shelf + brick width) of ceramic ﬁbre and placing it on the sand or directly on hard standing. Get the large kiln shelf centered exactly under the pulley position on the beam by using a plumb line. Make sure there is safe room for the ﬁrebricks, burners, and hoses.
Place the centred, base kiln-shelf on the ﬁbre and sur-round it with the interlocked eight bricks. Ensure the lowered drum sits on the bricks evenly and is vertical and plumb below pulley.
Place gravel outside the ﬁrebricks to hold them in place.
Place four half-bricks face down in the middle to support the smaller shelf, which has its corners cut off at marks 115 mm from the corners to make an octagon.
Sit the drum rim on the ﬁrebricks (you may need a helper) and ensure that it lines up evenly all the way round. Attach the shackles around the top of the drum and arrange the wire rope so that the drum will hang vertically and clamp it in place. Site the winch and pulley(s) so that the drum hauls cleanly.
Arrange the gas burner’s nozzle(s) just into the hole(s).
To make the burners and hoses safe I have bolt-ed them to house bricks and during ﬁring lean a concrete block on the bricks. Connect the regulator to a propane cylinder. Raise the drum with the winch and carefully place your work on the shelf. Use a second kiln shelf and ceramic “legs” for lots of small work. Lower the drum carefully and check through the ﬂue that the drum is centred and not touching the work. Insert the thermocouple in its sheath into the thermocouple hole and connect it to the multimeter, ensuring that the leads do not touch the kiln.
The thermocouple is inserted so it does not touch work when checked through the ﬂue. The two wires of thermocouple MUST NOT touch inside the sheath – I separate then with wisps of ceramic ﬁbre and a ﬁrebrick button.
If necessary, consult pottery literature and prepare the ﬁring time-line on graph paper (1 mv from thermocouple = 25º C.). Ensure that the burner tap(s) are off, air vents on burners are about one-third open and the ﬂue completely open.
Open the regulator on the cylinder, check for leaks (nose, liquid soap), turn the burner on only slightly and light. The ﬁrst ﬁring may produce fumes and it may be wise to wear a mask. Adjust the gas cylinder regulator burner tap(s) to achieve an appropriate rate of temperature rise.
The drum will get hot enough to burn severely so I wear welding gloves when very carefully peering obliquely through the ﬂue, or adjusting the ﬂue opening to be smaller (use a piece of kiln shelf to cover the ﬂue) when higher temperatures are needed towards the end of a glaze ﬁring. Then grab a comfortable chair, a drink and copy of The Shed magazine and wait for your artistic revelation.
I ﬁre during the day and let the whole cool down overnight.
40-gallon oil drum
Gas burners, pressure gauges, hoses, regulators
45 kg propane gas cylinder
Ceramic ﬁbre blanket, 3.8 metres of 610 mm x 50 mm
3 metres of nichrome wire
12 ﬁrebricks, standard 230 x 115 x 75 mm
kiln shelf 460 mm square kiln shelf 406 mm square
Steel wire rope
Three shackles, two wire rope grips
Nickel/chromium/nickel/aluminum thermocouple with ceramic sheath
Multimeter with a 200 mV (millivolt) range
* Specialist electrical suppliers or gas/kiln engineers can supply specialist parts. You may be able to get kiln shelves pre-cut to shape needed.