Firing and fixing · Loading and unloading a kiln

Shelves, posts, clearances and what can touch what.

Bisque and glaze firings want opposite things from you: a bisque load is packed and nested, a glaze load is spaced a finger’s width from everything. Under both, the same skeleton: three posts in columns, an inch from the wall, a cone on two shelves, and nothing opened above 200 degrees. Our staff load ours; this page is for a kiln of your own.

Four steps with a tick list at each: which firing, shelves and posts, cones and wash, and unloading. Six things that go wrong, and six videos of kilns being loaded.

This is the short version: bisque against glaze, the posts, the cones, the unload, each with a tick list. The reasoning, the packing notes and the questions are in the comprehensive version.

x3Posts per shelf, never four, in columns to the floor
200°Fahrenheit. Nothing opens above it
x6Videos, from makers who have nothing to do with us
x4Steps, each with a tick list you can work off
Jump to a section
Why this page has words and video The whole idea in three lines The load in six moves What you need at the kiln 1. Bisque or glaze 2. Shelves and posts 3. Cones and wash 4. Unloading Six videos of kilns being loaded The one video to watch When it goes wrong How it works at The Clay Hole Questions people actually ask Related lessons
An illustrated bearded potter in an apron loading bare clay mugs and jars onto a shelf on posts inside a round electric kiln with its lid swung open, shelves of pots behind him

Every step, the reasoning, the stacking notes and six videos.

Read it, then watch it

Why this is written down and filmed, both.

Loading a kiln is rules and a feel for a three-dimensional puzzle. The rules, three posts, an inch from the wall, a quarter inch between glaze, bisque can touch and glaze cannot, cones on two shelves, are a list a page holds. The puzzle, how a production potter fits sixty mugs into a load without a wasted inch, is a thing you watch. Our staff load our kilns, so this page is written for a kiln of your own, and for members who want to know why the drop-off rules exist.

Use both, in this order

Read the rules for the firing you are loading, bisque or glaze, because they are opposite. Watch a load of that kind packed. Then load with the tick list next to the kiln.

The whole idea

Bisque is packed. Glaze is spaced. Everything sits on three posts, an inch from the wall.

Bare clay can touch bare clay, so a bisque load is stacked and nested. Glazed clay is liquid glass at temperature, so a glaze load has a finger’s width around every piece, on cookies, naked bottoms. Three matched posts in columns to the floor, the bottom shelf off the floor, an inch from the wall, a cone on two shelves, nothing opened above 200 degrees. Our staff load ours.

The five-minute version

The whole load in six moves.

If you have loaded a kiln before and you just want the shape of it, this is the shape of it. Everything below is these six moves, slowed down and with the places they fail marked.

1Decide: bisque or glazeOpposite loads. Bisque stacks and nests. Glaze is spaced a finger’s width from everything.
2Bottom shelf on short postsNever on the floor. Three posts, an inch from the wall, level.
3Heavy low, tall in the middleDense pieces on lower shelves. Tall pieces mid-shelf, never at the edge near an element.
4Three posts, in columnsSame height, placed directly over the three below, all the way up. Half shelves to stagger.
5A cone on two shelvesBottom and top. The controller reads a thermocouple; the cone reads the firing.
6Lid down, and nothing opened above 200Crack the lid an inch at 200, open it all the way and unload at 150. Gloves, and a fingertip run round every foot.

Before the first shelf

What you need at the kiln.

Six things, and one of them is a plan. More posts than you think is the advice every potter gives after their first load.

Shelves and postsMore posts than you think, in a range of heights, three per shelf. Half shelves for staggering.
Kiln wash on the shelf topsBrushed on the top face only, never the bottom or the edges, and patched when a drip is ground off.
Witness conesThe cone you fire to, plus one below and one above, on the bottom and the top shelf.
Cookies and catchersUnder every glazed piece, and a catcher under anything that runs. Our catcher lesson is the method.
Gloves and a diamond padFor unloading a warm kiln, and a diamond pad kept wet, with glasses and an N95 or better, for the foot that picked something up.
A loading planTall pieces measured before they go in. A shelf set an inch too low for the tallest piece is a whole layer wasted.

Shelves and plenty of posts, kiln wash on the shelf tops, witness cones, cookies and catchers, gloves and a diamond pad, and a loading plan.

1

Step one

Decide which firing this is, because the two loads are opposites.

Bisque is packed. Glaze is spaced. In a bisque every piece is bare clay, and bare clay can touch bare clay: stacked, nested, rim to rim, foot to foot, lids on. In a glaze firing every glazed surface is liquid glass at the top, and anything it touches, it joins: a finger’s width from every neighbor and post, an inch from the wall, on a cookie, naked bottom.

Packed

Loading a bisque

Stack and nest, with two rules: nothing heavy on anything thin, and nothing wedged so tightly it cannot shrink, because clay shrinks in the bisque and a bowl jammed inside a bowl cracks both. Rim to rim for bowls, foot to foot for mugs, plates in short stacks, lids on. Packed close is fine; packed solid, with no route for heat and steam, is not. Packing a bisque well is a skill, and Florian Gadsby’s and ClayShare’s videos below show it being done.

Spaced

Loading a glaze

A quarter inch between glazed pieces is the minimum; a finger’s width is the habit. Nothing glazed touches a post, a wall, a neighbor or the shelf; every piece stands on a cookie with a bare foot, and anything that might run stands in a catcher. Lids only if the seat is bare and waxed both sides. Jonthepotter’s video loads a glaze firing in its last two minutes.

Both firings share the rest: dry work only, an inch from the wall, three posts, a cone. The bisque is where things explode, because it is the firing that meets water; the glaze is where things fuse, because it is the firing that makes glass. Our firing lesson, What a Firing Actually Does, is the reasoning under both.

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2

Step two

Bottom shelf on short posts, heavy things low, three posts in columns.

The first shelf sets up every shelf above it. It sits on short posts, never on the floor, so heat moves under it and the floor bricks are protected. Three posts, the same height, an inch from the wall, and a shelf that is level when you press each corner.

Then the load goes up in columns. Every shelf sits on three posts, never four, because three points always sit flat and four rock. Each set of three sits directly above the three below, all the way to the floor, so the weight travels down through posts and not through the middle of a shelf. Half shelves let one side of the kiln run tall while the other runs short, and a load with a few half shelves fits more than one with full ones.

Heavy, dense pieces go low and delicate ones go high. Tall pieces go in the middle of a shelf, never at the edge, because the edge is where the elements are; an inch from the wall is the rule for everything and the thermocouple gets a hand’s width. Measure the tallest piece before the shelf above it goes on, because a shelf set an inch too low will not clear the piece and the layer is wasted, and a shelf set an inch too high wastes an inch you could have used.

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3

Step three

Cones on two shelves, kiln wash on the tops, and the lid down.

The controller reads a thermocouple. The cone reads the firing. A witness cone bends when it has received a certain amount of heat over time, which is what a glaze cares about. One set on the bottom shelf and one on the top tell you whether the kiln fired evenly and told the truth.

A set is three cones: the one you fire to, one below it, and one above. The lower one bending first says you are close; the target bending says done; the upper one staying upright says not over. A cone pack in every load is how a potter knows the elements are aging before the pots say so, and it is the first thing to look at when a load comes out wrong.

Kiln wash goes on the top face of every shelf, never the bottom or the edges, and gets patched whenever a drip has been ground off. A washed shelf lets a small drip chip away; a bare shelf is a permanent home for it. Then the lid down, the peepholes plugged the way the kiln’s maker says, and the schedule set. Our kilns fire cone 05 for bisque and cone 5½ for glaze; yours fires whatever your clay and glaze were made for.

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4

Step four

Unloading has rules of its own: under 200, gloves, and a fingertip run round every foot.

Nothing opens above 200 degrees Fahrenheit. Crack the lid an inch at 200, open it all the way and unload at 150. A kiln opened hot hits its load with cold air, and the pots cool too fast; a plate with a thick base and a thin rim is the first to crack. Patience is free and plates are not.

Then gloves, because a warm kiln is still warm, and a fingertip run round every foot once the pot is cool to the touch: a glazed pot that picked up a grain of sand, a kiln wash flake or a neighbor’s drip has a foot that catches on a table, and a diamond pad kept wet, with safety glasses and an N95 or better on, takes it off in a minute. Read the cones before you move the shelves. Drips get ground off shelves wet, never dry, with safety glasses and an N95 or better on, and the wash patched before the shelf goes back in.

Bisque comes out chalky, rings when tapped, and goes straight to a shelf, not a wet table. Glaze comes out with a naked foot that might have a bump on it and a glaze that might have done something the diagnostic in our glaze problems lesson can name. Then the shelves get a HEPA vacuum or a damp sponge, never a dry sweep, the posts sorted by height, and the next load starts with the bottom shelf.

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Watch it done

Now watch six videos of kilns being loaded.

Watch this one, then go count your posts.

None of these makers work here. Between them they cover loading from the bottom shelf up: a kiln maker’s three minute overview, a bisque packed and unpacked, bisque loading tips, a look at kiln shelves that ends with a glaze load, the bottom shelf, and stacking a bisque in full. Nothing but the still frame loads until you press play.

A kiln maker’s three minute walk through loading greenware and glazed ware. The other five videos are in the comprehensive version.

Start here: loading in three minutes LOADING YOUR CERAMICS KILN FOR BEGINNERS // AMACO Classroom Kiln Basics AMACO Brent
A kiln maker’s three minute walk through loading: shelves on posts, then greenware for a bisque, then glazed ware. Watch it before you touch a shelf. Watch on YouTube
A bisque kiln, packed and unpacked How to Pack a Bisque Firing in the Electric Kiln and Speaking about My Craft Process Florian Gadsby
Seventeen minutes in a potter’s working week. The bisque kiln is packed in about the first minute, then come talk about a making routine and an exhibition, firing and unpacking the bisque, waxing bases, glazing cups and packing a gas kiln. Watch on YouTube
Bisque loading, the tips Bisque Fire Loading - Kiln Loading Tips and Tricks Pottery Crafters
Eight minutes on loading a bisque: setting up the kiln base, loading and stacking the pottery, why we bisque at all, final preparations and the firing temperatures. Watch on YouTube
Kiln shelves, and a load The BEST Kiln Shelves EVER! Glazing and Loading a kiln Jonthepotter
Nine minutes that are mostly a look at one maker’s kiln shelves and how they compare with old ones, with a kiln being loaded in the last two. The description links the shelf seller’s site, so treat the praise as a pitch. Watch on YouTube
The bottom shelf How To Set the Bottom Kiln Shelf In Your Kiln ClayShare
Three and a half minutes on setting the bottom shelf on short kiln posts, which the description says makes the kiln last longer and fire more evenly. Watch on YouTube
Stacking bisque, in full Stacking a bisque kiln (Kilns part 3) ClayShare
Fifteen minutes on stacking a bisque kiln: preparing the kiln, the first layer, spacing and height checks and adding shelves. The last few minutes set a kiln sitter, where the cone switches the kiln off, which is a different job from the witness cones on this page. Watch on YouTube

When it goes wrong

Six ways it goes wrong, and what to do about each.

The three failures that happen on the first load.

Pick the one that looks like your kiln. The first three are spacing, water and airflow.

How it works here

At The Clay Hole, our staff load and unload every kiln.

This page is written for potters with a kiln of their own. Here is what happens to your work between the drop-off table and the pickup shelf, and why the rules are what they are.

Three things to know here

Our staff load and unload every kiln; members put dry, finished, paid work on the drop-off tables and collect it from the pickup shelves. Every drop-off rule is a loading rule from this page: bone dry, a bare foot on a cookie or catcher every time (no cookie, no firing), a kiln ticket on glaze work. Bisque is cone 05 and free; glaze is cone 5½ at 5 cents a cubic inch, paid before drop-off.

The drop-off table

Bone dry, because a damp piece explodes in the bisque and takes its neighbors. For a glaze firing, a bare foot and a kiln cookie or glaze catcher under every piece, every time, no exceptions: no cookie means no firing, because a glazed foot fuses to a shelf. A kiln ticket with your order number on glaze work, so it comes back to you; bisque needs no ticket and costs nothing. Every one of those is a loading rule from this page, seen from the other side.

Why staff load

A kiln load is dozens of members’ work packed by a staff member who knows our kilns, and one badly placed pot can cost everyone on the shelf. Loading is a craft of its own, and here it is a staff craft. This page is so you know what they are doing and why your piece came back the way it did.

Firing and pickup

Bisque is cone 05 and free. The glaze firing is cone 5½ at 5 cents a cubic inch, $4.80 minimum, paid before the piece goes on the drop-off table. Fired work comes back to the pickup shelves; take it home within two weeks, because the shelves are shared.

Your own kiln

If you have one, every rule on this page applies to it, and the videos show kilns being loaded in other makers’ studios. Pots made here from our clay can go home bone dry to your own kiln, as long as both firings happen there, because our free bisque is paid for by other members’ glaze firings. Pots for our kilns are made from our clay, because a body we do not know at cone 5½ is a body that can spit on somebody else’s work.

Questions people actually ask

The ones that come up every week.

What is the difference between loading a bisque and loading a glaze?

Bisque is bare clay, and bare clay can touch bare clay: pieces can be stacked, nested, rim to rim, foot to foot, a bowl inside a bowl, as long as nothing heavy sits on anything thin and nothing is wedged so it cannot shrink. Glaze is liquid glass at temperature, and nothing glazed can touch anything: a finger width from every neighbor and post, an inch from the wall, on a cookie, with a naked bottom. Bisque is packed; glaze is spaced.

How far apart do things go?

A quarter inch between glazed pieces is the minimum and a finger’s width is the habit. An inch from the kiln wall for everything, in both firings. A hand’s width around the thermocouple. Between shelves, an inch above the tallest piece on the shelf below.

How do posts work?

Three per shelf, never four, because three points always sit flat and four rock. The same height as each other. Placed directly above the three posts on the shelf below, so every column of posts runs straight to the floor and the weight goes down through the posts, not the shelves. Half shelves let you stagger heights on each side.

Can lids fire on their pots?

In the bisque, usually, so they shrink together and fit. In the glaze firing, only if the seat is bare on both sides, waxed and cleaned, so the lid does not fuse to the pot. Many potters glaze fire lids on for fit and accept the wax work that takes.

What are cones for?

Witness cones are small pyrometric cones set on the shelf that bend when they have received a certain amount of heat over time, which is what matters to a glaze. The controller reads a thermocouple; the cone reads the firing. A cone on the bottom shelf and one on the top tell you whether the kiln fired evenly, and a cone in every load is how a potter knows the kiln is telling the truth.

When can I unload?

Not until the kiln reads 150 degrees Fahrenheit or less. Crack the lid an inch at 200, open it all the way and unload at 150. A kiln opened hot cracks its own load. Patience is free and plates are not.

Who loads the kilns at The Clay Hole?

Our staff, every load, bisque and glaze. Members put finished, dry, paid work on the drop-off tables and pick it up from the pickup shelves, and the whole of this page is what happens in between. It is written for potters with a kiln of their own, and for members who want to know why the drop-off rules are what they are.

Related lessons

Six lessons that sit next to this one.

Three to read next.

A kiln load is drying, catchers and glaze fit seen from the shelf. These are the pages on either side.

Firing and fixingWhat a Firing Actually DoesThe reasoning under the bisque, glaze and cone rules on this page. GlazingMaking a Glaze CatcherUnder anything that runs, in your kiln or ours. Firing and fixingFixing Fused and Sharp PotteryFor the pot that touched something. Trimming, handles and dryingHow to Properly Dry Your PotteryHow to dry work slowly and evenly, and why a wet core blows up in the bisque. GlazingGlaze Problems, Causes and FixesWhat the load is telling you when it comes out. FoundationsThe Many Myths of PotteryIncluding the one about air bubbles making a pot explode.

That is the whole load

Bisque packed. Glaze spaced. Three posts in columns. Cones on two shelves. Nothing opened above 200.

Your first load will have a shelf an inch too low and a mug you forgot to give a cookie, and the second will have a plan taped to the kiln. That is how everyone learns it, including the people who load ours. If you never own a kiln, now you know why the drop-off table asks what it asks.

If you want the reasoning, the stacking notes, the cone detail and the answers to the questions everybody asks, switch to the comprehensive version at the top. Otherwise, go count your posts.

Back to Clay Hole University What the firing does once the lid is down

Written for potters everywhere. Where our studio does things differently, the page says so.