Glaze running is what happens when melted glaze flows down the pot during firing and collects at the foot, on the shelf, or on the pot next door. A little movement is normal, but a real run can weld a pot to the shelf and ruin both.
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Quick Answer
Glaze running is usually caused by glaze applied too thickly, a firing that went too hot or held too long, or a glaze that is too fluid for the cone you fired. Apply thinner coats, keep glaze away from the foot, test unfamiliar glazes on a sloped tile, and protect shelves with kiln wash and catch dishes.
What Glaze Running Looks Like
Every glaze softens and moves a little in the kiln as it melts. Glaze running becomes a problem when it travels far enough to leave a thick bead at the base, drip off the pot, or glue the piece to the shelf. The signs are usually obvious once you unload.
Signs of a run
- A thick roll or bead of glaze along the bottom edge of the pot.
- Bare, thin glaze near the rim and a heavy pool at the foot.
- Drips on the shelf or on the pot below.
- A pot stuck to the shelf that will not lift cleanly.
Why it matters
Glaze running does not only spoil the pot. A glaze that fuses to a shelf can pull chunks out of the shelf when you chip it free, and a stubborn drip can crack the shelf as it cools. Our articles on kiln shelf thickness and kiln shelf spacing explain how shelves hold up and how to protect them.
Main Causes of Glaze Running
Most glaze running traces back to a handful of causes. Work through them in order, since the first few account for the majority of problems.
Glaze applied too thickly
The simplest cause is also the most common. A thick layer holds more melted glass than the surface can support, so gravity wins. Dipping for too long, or brushing on extra coats, quickly turns a well-behaved glaze into a runner.
Firing too hot or holding too long
Glazes are designed for a particular melt range. Go past it, or hold at peak temperature for a long time, and the glaze becomes more fluid. Check what the kiln did with witness cones, as described in our guide to witness cones for pottery kilns.
Wrong glaze for the cone
A glaze made for a lower cone will run badly at a higher one. For example, a mid-range glaze pushed into a high-fire kiln can flow right off the pot. Always match the glaze label to your firing range.
Layering and mixing glazes
Two glazes layered together can melt at a lower temperature than either alone, which makes runs more likely. Test any combination on a tile first. Our guide to pottery glaze layering explains how combinations behave.
Shape and slope
Vertical walls and steep slopes make glaze travel downhill. Textured and thick-walled forms behave differently from smooth thin ones. A glaze that sits well on a bowl may slide off a tall cylinder.
Glaze Running Symptoms and Fixes
The table below links the most common symptoms to the first fix you should try. Change one thing at a time and keep notes so you know what actually worked.
| Symptom | Likely cause | First fix |
|---|---|---|
| Heavy bead at the foot | Glaze too thick near the base | Leave more bare clay above the foot |
| Whole pot looks glassy and thin on top | Overfired or long hold | Check cones, shorten the hold |
| Only one glaze runs | Fluid recipe or too thick | Thin the coat, test on a tile |
| Combined glazes run | Mixture melts too easily | Reduce thickness of the top layer |
| Drips on shelf from pot above | Poor spacing | Increase gap or add a catch dish |
How to Stop Glaze Running Before You Fire
Prevention costs much less than cleaning up. Build a short routine into your glazing process so every pot gets the same careful treatment.
Control thickness
Dip for a consistent count of seconds and learn what your glaze should look like when dry. If you brush, apply even coats and let each dry. Our guide on how to apply pottery glaze walks through application methods and what thickness to aim for.
Keep glaze off the foot
Leave at least a quarter inch (about 6 millimeters) of bare clay above the base, and more for fluid glazes. Wipe the foot with a damp sponge so no glaze remains. A clean foot and a small bare margin give a run somewhere to stop before it reaches the shelf.
Use stilts, setters or catch dishes
For glazes you do not fully trust, set the pot on a small stilt or on a bisque dish made to catch drips. These sacrificial pieces are cheap compared with a ruined shelf, and many potters keep a stack ready.
Protecting Shelves from Glaze Running
Even careful potters get the occasional run, so protect the shelf. A thin, even coat of kiln wash gives drips a surface that releases rather than bonding permanently with the shelf. Scrape and recoat the wash between firings as needed.
Good kiln furniture also helps. Replace warped or pitted shelves, and keep a few spare half shelves handy. Browse our kiln shelves to compare sizes. Our guide on loading a pottery kiln for even firing shows how to leave enough room between pots so a runner cannot reach its neighbor.
Testing Glazes for Glaze Running
Never trust a new glaze on a favorite pot. A simple test tile tells you how far a glaze flows, long before you risk valuable work.
Build a run test tile
- Make a tile of your usual clay with a raised or angled surface.
- Apply the glaze at your normal thickness on the slope.
- Stand the tile on a spare piece of kiln shelf or a catch dish.
- Fire it with your normal program and a witness cone beside it.
- Measure how far the glaze moved, and note the cone and thickness.
Learn from every firing
Keep the finished tiles in a labeled box. Over time you build a library of how each glaze behaves on your clay, which saves guesswork and prevents repeat accidents.
Cleaning Up After Glaze Running
If a run does happen, take your time. Let the kiln cool completely. Wear safety glasses and a dust mask, because chipped glaze and shelf fragments are sharp and the dust is not healthy to breathe.
Use a small chisel to chip the drip off a washed shelf, working gently toward the edge rather than into the shelf. A silicon carbide stone can smooth what remains on the pot foot. If the shelf surface is torn out or cracked, replace it instead of risking a failure later.
When Glaze Running Is Useful
Some potters use controlled glaze running as a feature, in the form of waterfall effects, flowing ash glazes or drippy accents on sculpture. These pieces need to sit on a catch dish or a purpose-made setter so the glaze cannot damage the shelf.
Many reactive glazes move more than ordinary ones, so check our post on reactive glazes before using them on functional work.
Why Some Glazes Flow More Than Others
A glaze is a thin layer of glass, and like any glass it gets runnier as it gets hotter. The recipe decides how runny. Glazes with a lot of flux, which are the ingredients that help silica melt, become fluid quickly. Glazes with more alumina and silica stay stiffer, because those materials make the melt thicker.
Gloss, satin and matte
Glossy glazes are typically the most fluid, and a bright, clear gloss is the usual suspect when something runs. Satin and matte surfaces are often stiffer, but not always. Some matte glazes get their texture from crystals that form on cooling and are quite fluid when hot.
Reading a glaze label
Commercial glaze labels give a cone range and often a note about application thickness. Treat the recommended range as a hard limit. If a label says fire at a certain cone, and you want to experiment with a longer hold or a hotter finish, do it on a test tile first.
Pre-Firing Checklist for Glazed Pots
A quick look at each pot before it goes into the kiln takes seconds and prevents a lot of grief. Run through this list at the end of every glazing session.
- Is the glaze evenly applied, with no thick drips or pooled areas?
- Is the foot clean, with a bare margin above it?
- Are lids and their seats free of glaze where they touch?
- Are any combined glazes tested on a tile with this clay?
- Is the kiln program set to the right cone for every glaze in the load?
- Are the shelves washed and the pots spaced apart?
Answering yes to each question will not make glaze running impossible, but it will make it rare. Pair the checklist with notes after each firing and you will quickly learn how each glaze behaves in your own kiln.
Frequently Asked Questions About Glaze Running
Why does my glaze run only on the bottom of the pot?
Gravity pulls melted glaze downward, so any excess ends up near the base. Reduce thickness there and leave bare clay above the foot.
Can I fix glaze running by firing lower?
Sometimes, but only if the original firing was too hot. A lower firing can leave the glaze underdeveloped, so test before changing your program.
Is glaze running more common with certain glazes?
Yes. Very fluid glazes, glossy glazes with strong fluxes and layered combinations are likelier to run. Always test unfamiliar glazes on a tile first.
How do I remove a pot stuck to the shelf?
Wait until the kiln is cold, wear eye protection and gently chip around the foot with a small chisel. Do not pry the pot upward, as this can tear the shelf surface.
Final Thoughts
Glaze running is mostly a matter of thickness, temperature and tidy habits. Apply a controlled coat, keep the foot clean, test new glazes and protect your shelves, and you will avoid most of the heartbreak.
When you need new shelves or posts, see our kiln furniture, or ask us a question on the contact page. For technical reference on glaze materials, visit Digitalfire.
