|This the first in a series of tips on firing your kiln. Whether you
are new to firing, or experienced, you are sure to find something that
will improve your firing results.
Tip #48: Loading and Firing kilns: Part 1, Loading the Kiln
Most people do a bisque firing, then a separate glaze firing. We will
First some general thoughts about firing:
* Kiln vents assist greatly in simplifying firing and reducing firing
defects. In addition, they improve element life by removing damaging
fumes quickly. Of course, if you are firing in a structure where people
are working or living, a vent is required to remove the harmful fumes
from the area. This is true for bisque firing as well as glaze firing.
* You should regularly vacuum out the kiln, including the element
* New kilns, or kilns with new elements, should be fired once to Cone 6 without any ware in the kiln. This correctly oxidizes the elements and
ensures a longer life. They may smoke a little due to oil left on the
element wire during manufacturing. (Note: I found conflicting
information regarding the temperature of this first firing, everything
from Cone 04 to Cone 6. But general consensus now is that you
should fire to Cone 6 to fully oxidize the elements.)
* It is helpful to understand the changes that clay goes through in
firing. You can read about this a previous tip. Tip
31: Clay, the Drying and Firing Process
* Kilns should be placed at least 12-18" from all walls during
firing. Remove all combustible materials from the area around the kiln.
* All furniture and ware in the kiln should be placed at least 1” from
Loading the kiln
The bottom layer of shelving should be on 1/2" - 1" posts.
Your ware is placed on this first shelf, posts are set around the
perimeter, and another layer of shelving placed. Make sure you leave at
least 1/2" between the top of your tallest piece and the next
shelf, to allow for expansion during firing. Usually for whole round
shelves you will use 3 or 4 posts. For half rounds, you will use 3 posts
per side. Posts should be placed over each other as you rise up through
Some people believe that if you have half shelves, it is best to stagger
their heights to get more even heating. But after talking with many
potters I have concluded this is not very important in an electric kiln.
It is very important in a gas kiln, and that may be where the practice
Be careful placing and moving your pieces around. I have often broken
pieces while moving them slightly around. Instead of grabbing them at
their tops, lift them up from their bottoms.
Loading for Bisque Firing
Make sure your pieces are dry. Pieces that are still wet will feel cool
when placed on your cheek. Wet ware can blow up in the kiln, as the
water inside the clay expands.
Items may be stacked on and inside one another for bisque firings. They
won't stick together. However, you can cause problems by doing this.
* The carbons may not burn out completely from an area that is covered
by another piece, and this may cause defects during the glaze firing.
* Some items may break if they are not allowed to expand and contract
freely. So if stacking two bowls for example, make sure there is plenty
of room between them. Remember that items will shrink during firing.
* Stacking may cause more uneven temperatures throughout the kiln.
* Some people think the tighter they stuff the bisque load, the better.
And you may have success with this method. But other people find that
they do better when pieces are given space. My advice is that you can
pack a bisque load tighter than a glaze load, but don't overdo it.
Items such as plates and tiles often warp less if bisqued on their side.
You can lean them against the side of the kiln.
Fire items with lids in place, to prevent distortion.
Loading for Glaze Firing
* Leave at least 1/2" between all pieces. Remember that the piece
will expand during the firing cycle before it contracts and shrinks.
* If you have a vent, you don't have to worry about colors bleeding from
one piece onto another. If you don't fire with a vent this can be a
problem, so you might want to segregate colors while loading.
* Make sure you have a good layer of kiln wash on the shelf. This is to
facilitate the removal of glaze drips. Do not apply kiln wash to the
sides of the kiln, or underside of the kiln shelves. The wash is likely
to flake off land on your glazed pieces.
* Of course, glazed areas cannot be put directly on kiln shelves, or
they will fuse with the shelf. If doing low fire, place your pieces on
firing stilts. If doing mid to high fire, only glaze within 1/2" of
the bottom of your piece (sometimes more if you have a runny glaze.) Wax
the bottom of the pieces before glazing to make it easier to remove the
* If firing a new glaze you are unsure of, put the whole piece on a
piece of bisque you have pre-made. Then if glaze runs, it will run onto
this piece instead of ruining your kiln shelves.
For both Bisque and Glaze Firings
* Don't forget to add your witness cones while loading. You will want to
do this even if you have a kiln sitter or electronic controller, to see
what Cone was actually achieved inside the kiln. If you plan to use the
cones to determine when to turn off the kiln, make sure they are visible
through the peephole. Read Tip
42 for more information on Cones and Cone packs.
* Items such as large plates benefit from being in the center of the
shelf for even heating. This helps reduce warpage. For more information
26 on Plate and Platters, or Tip
30 on Making Tiles.
* If using an electronic kiln, make sure you place the shelves at
heights that avoid the thermocouples. The thermocouple should be at
least 1-2 inches from a kiln shelf or ware.
* If you have half shelves, it is perfectly acceptable to have them
staggered if it fits the size of your pieces. You can even use pieces of
broken shelves to add additional mini-shelves.
* It is usually easiest to put the tallest pieces on top, so you don't
have to use very tall kiln posts.
It is very useful to keep a firing log. Start your log entry by
describing how the kiln is loaded (types and sizes of items, density of
packing.) You will find that the more densely the kiln is loaded, the
longer it will take the kiln to reach the appropriate temperature. You
will learn how to adjust for this with your particular kiln. Typically
you will add a longer soak at the top temperature when the kiln is more
Copyright 2002 Cindi Anderson
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