Leather Hard Clay: Soft, Hard and What Each Is For
Leather hard is the stretch of drying when clay is firm enough to hold its shape in your hands and still wet enough to cut cleanly and bond to fresh clay. Trimming, handles, lids, carving, stiff slab boxes and hollowed sculpture all happen inside it, and in a dry studio it rarely lasts more than a day or two. Here is what is going on inside the clay, how to tell the soft end from the hard end, and which jobs belong to each.
Leather hard is clay firm enough to hold its shape and still wet enough to cut and join. At the soft end a thumb still leaves a print: that is where handles go on and pieces get joined. At the hard end only a fingernail marks it: that is where feet get trimmed, lids get cut and sculpture gets hollowed.
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Firm enough to hold, wet enough to work
Wet clay is tiny flat particles with water between them. As that water leaves, the particles pull closer and the piece shrinks. By leather hard most of that shrinking is done, but there is still water in the gaps.
That combination is the whole point. The clay is stiff enough to hold its shape while you press on it, and still wet enough that a tool slices it cleanly and fresh clay bonds to it. Wetter, it smears and slumps. Drier, it chips, makes dust and will not join.
The window has two ends. Soft leather hard is for joining. Hard leather hard is for cutting. Miss both and the piece goes on as it is, because bone dry clay does not come back evenly.
What to do at each end
- Find out which end you are at. Press a thumb into the base. A shallow print means soft leather hard. No print, but a fingernail still marks it, means hard leather hard. Cool against your cheek means there is still water in it.
- At the soft end, join things. Handles, knobs, spouts, feet, the next coil, the next section. Both pieces at the same stiffness, scored and slipped on both faces, pressed until a little slip squeezes out.
- At the hard end, cut things. Trim the foot, cut a box lid, hollow a sculpture, carve, burnish. The tool should take off one continuous ribbon.
- Trim before you handle. If the pot firmed up while you trimmed, close it in a bag for a few minutes so the wall evens out before the handle goes on.
- Hold it there between visits. A bag closed with no gaps holds a pot a day or two. A damp paper towel inside, not touching the clay, stretches that to about a week. Cover thin parts first.
- A little past is fixable. Bone dry is not. Mist it lightly and seal it in a bag for an hour. If it has gone pale and room temperature, leave it as it is and fire it.
Three things that go wrong
The handle cracked off at the join
The handle and the mug were at different stiffness, or the thin handle dried ahead of the thick wall. Match them before you join them, and drape a strip of plastic over the fresh handle so it slows down to the pace of the mug.
The rim went oval while you trimmed
Too soft to trim. Holding it down against the wheel head walked the rim out of round, and the tool smeared instead of cutting. Put it back on the shelf uncovered and trim something else first.
The tool skipped and threw dust
Too dry, or a dull tool. Dry clay throws powder and chips; a properly leather hard pot with stutter marks means the blade is finished. Stop rather than force a dry pot: the dust is silica, and a chipped foot does not mend.
What leather hard actually is
Wet, leather hard and bone dry are one material holding three different amounts of water. The drawing magnifies a sliver of clay at each stage: the gray plates are the clay particles, and the dots are water.
- Water holds the plates apart. Clay particles are flat, and in wet clay every one of them is wrapped in a film of water. That film lets them slide past each other, which is why wet clay takes any shape you push it into.
- Plates closing in. As the films evaporate, the plates draw together and the whole piece gets physically smaller. This is drying shrinkage, and most of it happens early, before and through leather hard.
- Water left in the gaps. At leather hard the plates are close enough to hold the shape, and there is still water in the pores between them. That leftover water is what lets a tool slice cleanly and fresh slip bond.
- Plates touch, gaps empty. Once the plates touch, the last water leaves from the gaps without making the piece much smaller. The clay goes pale, room temperature and brittle. That is bone dry.
- Most of the shrinking is done. This is why leather hard is the stage for joining. Two pieces joined here have little shrinking left to do, and they do it together. Join a wet piece to a leather hard one and the wet one keeps shrinking after the join is made.
The sentence worth keeping
Leather hard is the only stage where clay is stiff enough to push on and wet enough to cut and bond. Every job on this page needs both at once, which is why none of them can wait.
Why this is the stage to master
Most of what separates a good pot from a decent one is decided in a window that often lasts a single day here. Six reasons it carries that much weight.
It is the last stage that really joins
Score and slip still makes a true bond at leather hard. Past it, joins get weaker with every hour of drying, and a bone dry join barely holds at all. Every handle, knob, foot and seam has a deadline, and this is it.
It is the only stage that cuts clean
Wet clay smears under a tool and closes up behind it. Bone dry clay chips, crumbles and puts silica dust in the air. A crisp foot, a clean carved line and a lid that seats all come from clay that is firm and still damp.
It is the last stage you can change the shape
A dent still pushes out, a rim that went slightly oval can still be eased round, and a crack caught early can still be closed. Past leather hard, forcing any of those cracks the piece instead.
It decides the weight and the balance
Trimming is where a heavy bottom becomes a light pot and where the foot gets its shape. You cannot add thickness back at leather hard, but you can take it away cleanly, and you cannot do either later.
Most decoration lives here
Carving, fluting, faceting, chattering, sgraffito, mishima, stamping and burnishing all want clay that holds a mark and takes one. Underglaze can go on here or at bone dry.
It will not wait for you
This is a desert and the studio is dry. A pot thrown one evening is often ready the next day, and thin walls can be ready the same night. Knowing how to hold the window open is as much a skill as anything you do inside it.
Soft leather hard and hard leather hard
Leather hard is a range, not a moment. The soft end is for joining, the hard end is for cutting, and the middle is where most carving happens.
| Soft leather hard | Hard leather hard | |
|---|---|---|
| A thumb | Leaves a shallow print if you press | Leaves nothing |
| A fingernail | Sinks in easily | Still marks it, with some effort |
| The wall | Gives a little when you squeeze | Holds its shape under real pressure |
| The color | Still close to the wet clay | Visibly lighter than clay from the bag |
| Against your cheek | Cool | Still cool, not room temperature |
| Good for | Handles, knobs, spouts, feet, the next coil or section, features on a figure, easing a warp | Trimming a foot, cutting a box lid, hollowing a sculpture, fine carving, burnishing |
| Goes wrong when | You lean on it: it dents, and a trimmed rim walks out of round | You bend it: it cracks instead of flexing |
Two names or three
Some potters, and our carving and sgraffito lesson, split the window three ways: soft, mid and dry leather hard. It is the same window. The middle is where most carving, sgraffito and mishima are easiest, and the two ends still do the jobs in the table.
- Thumb leaves a shallow print. Press the pad of your thumb into a wall or a base you will trim away anyway. A soft, shallow dent means the soft end.
- The wall still gives. Seen in section, the wall dips under the thumb without cracking. Clay that still flexes like this will take a handle and squeeze back into shape.
- Thumb leaves nothing. The same press on a pot at the hard end leaves no mark at all.
- A fingernail still marks it. A small, clean nick, and no clay on your nail. Clay on the nail means it is softer than you thought. No mark at all means it has gone past leather hard.
Six ways to read it, in the order we use them
- The thumb. On a part you will trim away or cover. A print means soft; no print means you are past the soft end.
- The fingernail. A clean dent means you are still in the window. No dent means you have left it.
- The cheek. Hold the pot against your cheek. Cool means water is still leaving it. Room temperature means it is close to bone dry.
- The color. Clay lightens as it dries. Compare the part you want to work on with the thickest part of the same piece, which is always the last to change.
- The lift. Pick a thrown pot up by the rim with one hand and no support underneath. If you are afraid to, it is too soft to trim.
- The tool. A trimming tool at the right moment takes off one continuous ribbon. Smearing means too soft. Powder and chips mean too dry.
On the wheel
Throwing makes the shape. Leather hard is where a thrown pot gets its foot, its weight, its handle and its lid.
- Trim the foot toward the firm side. The pot should hold its rim under real pressure on the wheel head and feel something like hard cheese. Too soft and the tool tears a furrow while the rim walks out of round. Too dry and the tool skips and throws powder. Our trimming lesson has the whole method.
- Round every cut edge before it leaves the wheel. A damp sponge or a chamois over a freshly trimmed foot. A sharp leather hard edge becomes a brittle bone dry edge, then a chipped bisque edge, then a sharp edge under the glaze for good.
- Fit lids at the same stage as the pot. Measure the gallery and the lid with calipers and trim the lid to fit while both are leather hard. Two pieces at the same stage have the same shrinking left to do, so a lid that fits now still fits after the firing. Our lids lesson covers the throwing.
- Handles, knobs and spouts go on at the soft end, on both pieces. Firm enough to hold the pot without denting it, damp enough that a fingernail still marks it. Score both faces, slip, press until a little squeezes out, and blend the seam. Our handles lesson has every method.
- Trim first, then handle. Trimming means holding the pot upside down under pressure, and a handle in the way makes that a wrestling match. If the pot firmed up while you trimmed, close it in a bag for a few minutes so the moisture evens through the wall before the handle goes on.
- Facet, flute and chatter after the foot. A faceted pot has nothing round left to center on, so the foot comes first. A wire takes facets most easily toward the soft end; a knife or a rasp works nearer the firm end. Chattering happens on the wheel during or after trimming, while the clay still takes a mark.
- Ease the shape while it still flexes. A dent at the soft end often pushes back out from the inside with a rib and a hand supporting the outside. A rim that went slightly oval can be coaxed round with damp fingers and a sheet over it for a day. Past leather hard, forcing either cracks it.
- Burnish at the hard end. Rub firm leather hard clay with the back of a spoon or a smooth stone and the surface particles lie flat and shine. Glaze undoes it, and our firings soften or erase a plain burnish, so read our burnishing lesson before you plan on one.
- Smears and clogs the loop. Too soft. The clay packs into the tool instead of curling through it.
- Rim walks out of round. The pressure that holds a soft pot to the wheel head slowly pushes its rim oval, and you only see it when you turn the pot back over.
- One continuous ribbon. Leather hard. The tool takes off a long, springy curl and the sound is a steady hiss rather than a stutter. Trim now.
- Chips and dust. Too dry. The dust is silica, which is reason enough to stop. Bag the pot with a damp paper towel beside it and come back.
- A chip you cannot fix. A dry foot edge breaks rather than cuts, and that chip goes all the way through the firings.
Hand building
Soft clay bends and wraps. Leather hard clay stands up on its own. Knowing which one a project needs is most of what hand building asks of you.
- Stiff slab boxes want firm slabs. Roll and rib the slabs, then wait until you can lift one by a corner without it drooping. Under loose plastic in our studio that is somewhere between one and three hours, depending on the day and the clay. Soft slabs bow and slump the moment they are asked to stand as a wall.
- Cut the corners clean. Firm slabs take a straight cut and a true 45 degree bevel; soft ones drag and tear. Butt the walls, or bevel both edges so the seam sits right on the corner, as the drawing shows.
- Score and slip every face that touches another. Real scratches and real slip on both sides of every join, and a thin coil pressed into every inside seam. Firm slabs do not merge by pressure the way soft ones do, so the join has to be made.
- Build it closed, then cut the lid at firm leather hard. A sealed box holds its walls apart while you handle it. Cut too soft and the blade drags the walls inward and leaves an edge you cannot clean. Our lidded boxes lesson walks the whole build.
- Coil and pinch builds rise in stages. Let the section below firm toward soft leather hard before the next one goes on, so it carries the weight without slumping. Keep the top edge you are joining to damp with a sponge, so the new coil meets clay at its own stiffness.
- Feet, handles and lugs follow the same rule as on the wheel. Both pieces at the soft end, scored and slipped on both faces, covered loosely afterward so the thin part does not race ahead of the body.
- Soft slab work happens before leather hard, not during it. Wrapping a slab around a form or draping one on one of our slab molds needs a slab that bends. A leather hard slab asked to bend cracks along the outside of the curve. Once the piece holds its shape, it comes off the slab mold and the leather hard jobs begin.
- Seam shows on the side. In a butt joint the long wall runs to the corner and the short wall presses against its inside face, so the seam line shows on one outside face of the box.
- Both edges cut at 45 degrees. Hold the knife at 45 degrees to the table and draw it along each edge in one steady pass. Only a firm slab keeps that angle as you cut.
- Seam sits on the corner. The two bevels meet along the diagonal, so the seam lands exactly on the corner where nobody looks for it.
- Thin coil in the inside seam. Pressed into the inside corner and blended into both walls. It is the strength you will never see once the lid is on.
Sculpture
Sculpture is where leather hard stops being about neatness and starts being about whether the piece survives the kiln.
- Nothing thicker than an inch goes in the kiln solid. Anything thicker anywhere is built hollow from the start or modeled solid and hollowed out later. Our sculpting lesson sets the rule and the reasons.
- Hollow at firm leather hard. A fingernail marks it and a fingertip does not. Softer, and cutting it open lets it sag out of the shape you modeled. Drier, and the halves will not rejoin properly.
- Cut it open where the seam will hide. One clean pull of a wire through the base, the back or behind the ears, never through the face.
- Scoop to even walls. A loop tool takes the core out until every wall is three eighths to three quarters of an inch, checked with a needle. Even matters more than the exact number: a wall thin in one place and thick in the next dries at two speeds and pulls apart at the boundary.
- Close it like any other join. Score and slip both faces, press the halves together, and blend the seam with a coil inside and out.
- Put a pinhole somewhere hidden. A sealed form does not burst from trapped air. It bursts because the damp inside cannot dry, and that water turns to steam in the kiln. One needle hole lets the inside dry and the steam out.
- Add features and limbs at the soft end. Eyes, noses, ears, arms and tails are pressed and added while the figure still takes a fingerprint, scored and slipped at matching stiffness, then the thin parts covered while the body catches up.
- Carve the fine detail as it firms. Crisp edges, hair and texture cut cleanest toward the hard end. Between visits the piece lives in a bag with a damp paper towel beside it, and it dries for weeks before it is fired.
- Cut where the seam will hide. Behind the ears, straight down to the base, so the face stays whole.
- Over an inch solid: hollow it. A solid core this thick holds water long after the outside is dry, and that water is what breaks it in the kiln.
- Even walls, 3/8 to 3/4 inch. Scooped with a loop tool and checked with a needle all the way round.
- Scored, slipped and blended. Both faces scored and slipped, pressed together, and the seam blended with a coil.
- A pinhole lets steam out. One needle hole through a hidden spot, here the base, into the hollow inside.
Nineteen jobs that belong to leather hard
Every one of these needs clay that holds its shape and is still damp. Do them at leather hard or do without them.
| The job | Which end | Why it has to be now |
|---|---|---|
| Trimming a foot ring | Firm | Soft clay tears and walks out of round; dry clay chips and makes dust |
| Rounding cut edges with a sponge or chamois | Right after trimming | A sharp edge left to dry becomes a chipped bisque edge |
| Fitting a lid to its gallery | Both pieces at the same stage | Pieces at the same stage shrink together from here on |
| Attaching a pulled handle | Soft, on both pieces | The last stage a join truly bonds, with little shrinking left to pull it apart |
| Knobs, lugs, spouts and feet | Soft, on both pieces | Same reason as a handle |
| Faceting | Soft for a wire, firmer for a knife or rasp | Wet clay drags; dry clay will not slice |
| Chattering | During or after trimming | The flexible blade has to bounce off the clay to mark it, and only firm clay lets it |
| Carving, fluting and relief | Middle | Wet clay smears; dry clay crumbles and cracks |
| Sgraffito through slip or underglaze | Middle, finest detail a little drier | Too soft and the line closes; too dry and the coating chips |
| Mishima | Carve in the middle, scrape once the fill goes matte | Scraping bone dry clay makes silica dust |
| Stamping a maker’s mark | Middle | Wet clay blurs the stamp; dry clay will not take it |
| Burnishing | Hard | The particles only lie flat while there is a little water left |
| Building a stiff slab box | Firm | Soft slabs bow; only firm ones stand as walls and cut true |
| Cutting the lid off a closed box | Firm | A soft box drags the blade and pulls its walls in |
| Adding the next coil or section | Soft, on the section below | Firm enough to carry the weight, soft enough to bond |
| Hollowing a solid sculpture | Firm | Holds its modeled shape when cut open, still rejoins |
| Adding features to a figure | Soft | Pressed and added parts bond while the clay still flexes |
| Easing a dent or an oval rim back | Soft | Clay that still flexes moves; drier clay cracks |
| Closing a hairline crack | As soon as you see it | A crack at leather hard can be scored, slipped and closed; a dry one is a crack for good |
Holding the window open
In a dry studio the useful skill is not speeding pieces up. It is holding them still until you are back.
- A bag with a little air, closed with no gaps. The smallest bag the piece fits inside. It evens the moisture out overnight and holds the window open for a day or two. A bag only laid over the top lets air in round the edges, and the piece is mostly dry when you see it again.
- A damp paper towel for longer. Stand it beside the piece or lay it on the bat, never on the clay. It keeps the air in the bag humid and holds leather hard for about a week. Our cotton or plastic lesson covers which cover each piece needs.
- Cover the thin parts first. Rims, handles and spouts dry ahead of the body. A strip of plastic over a fresh handle slows it to the pace of the mug underneath it, and that one habit prevents most handle cracks.
- Weeks-long projects go home. A plaster damp box holds leather hard for weeks, and because it is plaster it lives at home, never in the studio. Our damp box lesson shows how to make one and how to carry pieces between the two.
- A little past can come back. Mist it lightly and seal it in a bag, and a pot only just past leather hard usually returns in about an hour. One further gone wants a barely damp cloth beside it, not touching, for a full day, so the water evens through the wall. Spraying a dry pot and trimming it twenty minutes later cracks the base, because the outside is wet and the inside is still hard.
- Bone dry does not come back. Soaking it to try cracks it. Leave the base as thrown, fire it as it is, and never scrape or sand bone dry clay: that puts silica dust in the air.
- Heat firms a surface, not a piece. Our hanging heat lamps stiffen a face or a rim in minutes, but the inside stays wet, and anything with a handle or a join on it is off the table. Our heat lamp lesson says when to use them. The torches at the wheels are Owner Only and never a drying tool.
What goes wrong, and what it means
Nearly every leather hard failure is a timing problem that looks like a technique problem.
A handle crack, days later
The handle and the mug were at different stiffness, or the thin handle dried ahead of the thick wall and the wall kept shrinking under it. Match the pieces, score deeper than feels polite, and sheet the handle afterward.
A rim that came off the wheel oval
Trimmed too soft. The pressure of holding it down walked the rim out of round. At the soft end, a sheet and damp fingers can sometimes ease it back over a day.
Stutter marks and dust
Either too dry or a dull tool, and you can tell them apart in seconds: dry clay throws powder and chips at the edges, while a properly leather hard pot that still stutters means the blade is finished.
A box that opened at a corner
Under scored, under slipped, or slabs at different stages. A firm slab does not merge by pressure, so the scratches, the slip and the inside coil are the whole join.
Sgraffito lines that closed up or chipped
Closed up means the clay was too soft and slid back in behind the tool. Chipped edges mean the coating and the clay had gone too dry. The middle of the window is where clean lines live.
A sculpture that cracked in the bisque
Too thick somewhere, sealed with no pinhole, or walls uneven enough to dry at two speeds. Hollow it at firm leather hard, check every wall with a needle, and give it weeks to dry.
The ones that come up at the shelves
How long does it take to get to leather hard?
It depends on the wall thickness, the clay, the cover and the weather. In our dry studio a thrown pot is often ready the next day, and a thin one can be ready the same night uncovered. Firm slabs for a box take one to three hours under loose plastic. Check rather than count hours.
Can I speed a piece up to leather hard?
You can stiffen a surface. A heat lamp firms the face pointed at it in minutes, which is right for a slab on a slab mold or a rim that needs to stand. It does not make the whole wall leather hard, and anything with a handle or a join on it should not go near one. Time and an open shelf are the even way.
Is leather hard the same as greenware?
Greenware means any unfired clay piece, so a leather hard pot is greenware, and so is a bone dry one. Leather hard is one stage within greenware.
Why does everyone describe leather hard differently?
Because it is a range and people slice it differently: two ends, or soft, medium and stiff, or early, middle and late. Every version agrees on the order. Joining sits at the soft end, cutting toward the firm end, and most carving in the middle.
Does porcelain behave the same way?
It goes through the same stages, but it is less forgiving. Porcelain grows brittle as it stiffens, which makes deep cuts in a foot ring harder near the dry end. Trim and carve the porcelain on our shelf a little earlier in the window than you would stoneware.
Can I put color on at leather hard?
Underglaze and slip, yes. Both go on raw clay at leather hard or bone dry, and slip decoration works best toward the firm end, because the piece softens as the water goes back in. Glaze waits for the bisque: brushed on leather hard ware it flakes off as the clay keeps shrinking underneath.
My pieces dry faster on one side. Why?
Air moves past one side more, or one part is thinner. Rims and handles always lead, and a piece by a door or a vent dries on the side facing it. Cover the side or the part that is ahead and leave the rest open until they match.
Is there a damp room or damp box I can use?
No. Damp boxes are plaster, and wet plaster and plaster dust stay out of our building because a single chip in reclaimed clay blows a crater out of somebody’s pot. A sealed bag with a damp paper towel inside holds leather hard for about a week on your shelf.
Where to go next
The five stages of clay
Wet and plastic, leather hard, bone dry, bisque and stoneware: where this window sits in the life of a pot.
Read it →Trimming and turning on the wheel
The biggest leather hard job, in full: the tests, the tools, fixing the pot down and the foot itself.
Read it →How to pull pottery handles
Pulling, shaping and attaching handles at soft leather hard so they stay on.
Read it →Score and slip a join that survives
Why two pieces at different stages crack apart, and how to make a join that holds.
Read it →A beginner’s guide to sculpting
Solid or hollow, the inch rule, hollowing at leather hard and the long drying sculpture needs.
Read it →Cotton sheets or plastic bags
Which cover holds a piece at leather hard and which one moves it on, piece by piece.
Read it →The day you come back decides the pot
Strip away the tools and the techniques and leather hard is a simple fact about water. The particles have stopped closing in, so pieces joined now stay together, and there is still water between them, so a tool still slices clean. That overlap lasts a day or two, and almost everything that makes a pot feel finished happens inside it.
Very often the difference between a potter with options and one without is knowing which day to come back, and having bagged the piece properly so it waited. Press a thumb, press a nail, hold it to your cheek, and you will know which end of the window you are holding and what it is ready for.
Leather hard is clay firm enough to hold its shape and still wet enough to cut and join. Join at the soft end, cut at the firm end, trim before you handle, and keep the piece bagged so the window waits for you.
For the full story, what is happening inside the clay and the leather hard jobs on the wheel, in hand building and in sculpture, switch to the Comprehensive Version at the top of the page.
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