A glaze firing has a way of finding the one spot you didn't check. The rim is fine, the belly is fine, and then there's a bare patch on the shoulder where the glaze crawled and a pinholed foot ring you'll be sanding for twenty minutes. Glaze problems feel personal, but they're rarely random. Almost every disappointing pot traces back to one of about ten habits involving thickness, mixing, dust, fit, or firing — and each one has a fix that doesn't require new equipment or a new recipe. Here are the ones that come up most often, and what to do about them.

Thickness: The Mistake Behind Most Others

Thin glaze looks washed out, dry, or scratchy, and it often breaks to bare clay on edges. Thick glaze pools in the foot, drips onto the shelf, crawls away from rims, and blisters where trapped gas can't escape. Many dipping glazes want somewhere around a millimeter of dry glaze on the pot — a bit more than the thickness of a business card. If you don't know what that looks like on your glazes, you're guessing every time.

Three habits fix most of it:

• Stir before every dip. Heavier materials settle first, so the bottom of the bucket is a different glaze than the top.
• Count your dips. Pick a duration — three seconds, five seconds — and use it consistently. Note it on the bucket so future-you knows.
• Measure. A notched glaze gauge or a needle pressed into dry glaze tells you the real number instead of a guess.

If you've already over-glazed a pot, scrape the excess while it's dry with a rasp or a piece of sandpaper, then smooth the edges with a damp finger. Under-glazed spots can be touched in with a brush and a thin second coat, feathered at the edges so the difference doesn't show.

Mixing and Specific Gravity

Every time you top up a settling bucket with water, you change the recipe. A glaze that was perfectly suspended last month can be watery sludge today without any ingredient changing. The reliable approach is to weigh dry materials by weight rather than volume, sieve them — 80 mesh is a common standard — and then check the bucket's specific gravity rather than trusting your eye.

To check it, stir thoroughly, weigh 100 ml of glaze, and compare. Many dipping glazes sit in the neighborhood of 140–150 grams per 100 ml, but your recipe and your clay may want something different, so record what works and repeat it. If the glaze is too thick to dip evenly, add water in small amounts. If it settles into a brick within an hour, a small addition of Epsom salts dissolved in water helps many glazes stay suspended — add a spoonful at a time, because too much will gel the bucket.

Dirty Bisque and Contaminated Surfaces

Crawling, pinholes, and bald patches are often not glaze faults at all. They're surface faults. Dust left from sanding, fingerprints, hand lotion, hair, and oils from handling all create a layer the glaze won't bond to, and the glaze pulls away in the kiln. Over-fired bisque can do the same thing, because the clay has closed up and won't absorb water from the glaze.

Before glazing, wipe each piece with a barely damp sponge and let it dry completely. Handle pots by the foot or wear clean cotton gloves. Don't set glazed ware on newspaper, and don't touch a glazed surface with bare hands before it goes in the kiln — it only takes one fingertip to make a pinprick. If you use wax resist, make sure it has fully dried before dipping, and keep it off any area you intend to glaze.

Feet, Shelves, and Glaze on the Bottom

The classic beginner mistake is glazing all the way to the foot and welding the pot to the shelf. Clean the bottom of the pot properly: leave roughly 5–6 mm of bare clay at the foot, wax it before dipping, and wipe away any glaze that creeps past the line with a damp sponge while it's still wet. Run a finger around the foot after every dip — it takes five seconds and saves a shelf.

Kiln wash your shelves, and if a glaze is a known runner, set the pot on a waster bisque tile or a shallow dish of alumina so the drip lands somewhere harmless. Stillts help for small pieces, but they leave marks and they don't forgive a glaze that flows hard. If a piece does stick, don't pry it — chip the glaze away with a tile nipper or grind it free rather than cracking the pot.

Firing Too Fast: Blisters, Pinholing, and Runs

Glaze needs time. Rushing the climb traps carbon and gases under a glaze that has already sealed over, and no amount of hoping will heal that. A modest soak at the top of the firing — holding the peak temperature for ten or twenty minutes — lets blisters smooth out and pinholed surfaces close.

Carbon burnout is the other half of the story. Organic material in the clay has to burn out well before the glaze melts, so a bisque firing that climbs slowly through the lower ranges, with a soak before the glaze begins to fuse, prevents a lot of pinholing later. If your kiln controller and your cone pack disagree, believe the cone. And slow the cooling through the last couple hundred degrees, where fast cooling causes dunting and can leave glazes dull or crazed.

Crazing and Shivering: When Glaze Doesn't Fit the Clay

A crazed glaze is one that contracts more than the clay body as it cools; a shivering glaze contracts less and flakes off edges. Both are fit problems, not application problems, and they won't be fixed by dipping thinner.

Fixes usually involve more silica in the glaze for crazing, or a clay body with lower expansion, or a change in firing temperature. Change one variable at a time and fire a test tile. If a glaze crazes only on one body, the body is as much of a suspect as the glaze. Keep in mind that heavily crazed surfaces are hard to clean and many potters avoid them for food use with acidic dishes and drinks. For anything you plan to sell, test fit on the clay you actually use, not the one you had last year.

Layering Blind, Labeling Nothing

Layering two glazes is one of the most rewarding things in ceramics and one of the easiest ways to ruin a kiln load. Two thin coats behave nothing like one thick coat, and a cone 6 glaze under a cone 10 glaze is a chemistry experiment you didn't mean to run. Test on tiles first, note the order and the number of coats, and remember that the top glaze generally dominates.

Label everything. Buckets get a name, a cone, and a date. Test tiles get written on with a glaze pencil or tagged before firing, along with the coat count. A glaze notebook with a tile taped beside each entry is worth more than any recipe you find online, because it records what actually happened in your kiln.

The Ten Mistakes, in One Checklist

Before the next glaze firing, run down this list. It takes ten minutes and prevents most of what goes wrong.

1. Glaze applied too thin or too thick — measure instead of guessing.
2. Bucket not stirred and specific gravity unknown — check both.
3. Recipe mixed by volume — weigh dry materials instead.
4. Glaze not sieved — lumps become pinholes and spit marks.
5. Dust, oil, or fingerprints on bisque — wipe and handle with clean gloves.
6. Glaze on the foot — wax, wipe, and check with a finger.
7. Firing too fast — soak at the top and slow the lower climb.
8. Ignoring cone packs — verify the controller's numbers.
9. Glaze that doesn't fit the clay — test on real tiles, adjust one thing at a time.
10. No records — label the bucket, note the coats, keep the tile.

None of this requires a better recipe or a bigger kiln. It requires slowing down in the ten minutes before the lid closes. Do that, and the firing you open next week will look a lot more like the one you pictured.

Photo: phamkhanhquynhtrang / Pixabay