Why Your Pottery Glaze Has Pinholes (And How to Fix It)

Few things are more frustrating than pulling a piece out of the kiln only to find your glaze covered in tiny holes. You did everything right or so you thought. The good news? Pinholes are one of the most common glaze defects in ceramics, and once you understand what causes them, they’re usually fixable.
This guide walks you through the main causes of glaze pinholes and, more importantly, what to do about them.

What Are Glaze Pinholes?
Pinholes are small, sharp-edged holes that appear on the surface of fired glaze. They look like the glaze was punctured with a pin which, in a way, is exactly what happened. During the firing process, gases escape through the molten glaze, and if the glaze heals over too quickly (or not at all), those gas escape points become permanent holes.
Pinholes differ from pitting (wider, shallower craters) and crawling (glaze pulling away entirely), though the root causes often overlap.

7 Common Causes of Glaze Pinholes

1. Glaze Applied Too Thick
   Thick glaze layers trap gases underneath. As the kiln heats up, those gases push through the molten glaze and punch holes that the glaze doesn’t have time to fill back in.
   Fix: Aim for even, controlled application. For most dipping glazes, 1–2mm is the sweet spot. Use a glaze hydrometer or thickness gauge to stay consistent.
2. Glaze Applied Too Thin
   Counterintuitively, glaze that’s too thin can also pinhole. A thin layer may not have enough molten material to flow back over the gas escape point.
   Fix: Check your specific glaze manufacturer’s recommended thickness. If you’re mixing your own, keep a log of specific gravity measurements so you can replicate results.
3. Dusty or Contaminated Bisqueware
   Dust, oils from your hands, or residue from kiln wash on the bisque surface can cause outgassing during firing. The gas has nowhere to go but up through the glaze.
   Fix: Wipe bisqueware down with a clean, barely damp sponge before glazing. Avoid touching the surface with bare hands after cleaning. Make sure your bisque pieces are stored in a dust-free environment.
4. Underfired Bisque
   If bisqueware hasn’t been fired to the correct temperature, it retains more organic material and moisture. When it’s refired with glaze, that material burns off and the resulting gases push through the glaze layer.
   Fix: Ensure your bisque firing reaches the correct cone for your clay body. Most stoneware bisque fires to cone 06–04. Check your kiln’s performance with witness cones — don’t rely solely on a digital controller.
5. Firing Too Fast Through the Critical Range
   If your kiln heats up too quickly between roughly 1000°F and 1100°F (540°C–593°C), organic material in the clay burns off too rapidly. The rapid outgassing can punch holes in the glaze that forms above those temperatures.
   Fix: Add a slow segment in your firing schedule through this range — around 100°F (55°C) per hour works well for most clay bodies. This is sometimes called a “carbon burnout” hold.
6. Not Enough “Soak” at Top Temperature
   If your kiln reaches peak temperature and immediately begins cooling, the glaze may not have enough time to flow and self-heal over any gas pinholes.
   Fix: Add a soak (hold period) at peak temperature — typically 10 to 20 minutes for most stoneware and porcelain firings. This gives the molten glaze time to level out and close up any surface defects.
7. Glaze Chemistry Issues
   Some glaze recipes are simply prone to pinholes because of their chemistry. Glazes high in zinc oxide, titanium dioxide, or certain colorants (especially those with high iron content) are more likely to pinhole.
   Fix: If you’re consistently getting pinholes with a specific glaze, try adding a small amount of Gerstley Borate or Ferro Frit 3134 to improve melt fluidity. If you’re using commercial glazes, check whether the manufacturer has a firing recommendation you may be deviating from.

A Quick Troubleshooting Checklist
Before your next firing, run through this list:
∙ Is my glaze the correct thickness? (Tested with hydrometer or thickness gauge)
∙ Did I clean my bisqueware before glazing?
∙ Was my bisque fired to the correct cone?
∙ Does my firing schedule have a slow ramp through the carbon burnout range?
∙ Am I soaking at peak temperature?
∙ Is this a glaze recipe known to be prone to pinholes?

When Pinholes Keep Coming Back
If you’ve addressed the above and still see pinholes consistently, it’s worth testing one variable at a time rather than changing everything at once. Fire test tiles alongside your work and keep notes on glaze thickness, firing schedule, and clay body. Over time, patterns will emerge.
Also consider whether the issue is specific to one glaze, one clay body, or one area of the kiln. Pinholes that appear only on the bottom shelves, for example, may point to a kiln venting or heat distribution issue rather than a glaze problem.

The Right Equipment Makes a Difference
Preventing glaze defects isn’t just about technique — it’s about having equipment that fires consistently and reliably. An accurate kiln controller, properly functioning elements, and well-placed witness cones all reduce the guesswork that leads to repeated firing problems.
At The Kiln Shop, we stock kilns, controllers, pyrometers, and accessories designed for potters who take their craft seriously. Whether you’re troubleshooting an existing setup or building a new studio, we’re here to help.
Browse our kiln range