Trouble shooting glaze issues

You could be a brand new ceramic hobbyist or a gallery-seasoned professional potter, the Kiln Gods spare no one. Even the most skilled of us are occasionally humbled. If you’ve ever made more than a few pieces, you’ve probably had glaze issues. Maybe you have held a dirty fist to the sky and asked the Kiln Gods, “Why? Why didn’t my glaze come out right?”

As you know, lots of things affect the glaze outcome, including off gas from neighboring pieces, mixing of the glaze, clay body fit, temperature, method of application etc.

In order to attempt an answer why your glaze didn’t come out as expected, we’ve got to talk about the issue. *feel free to comment below on your own experiences and knowledge. For this, I did some research and pulled from my own personal glaze mistakes.

  • Color was ‘off’. Too dark? Too light? Did you stir between strokes? Did you apply enough glaze (2-3 coats)? Maybe the bottle is contaminated? But what kind of clay did you use? Many times I’ve used glazes on dark brown/red brown clay and I’ve gotten mixed results. Sometimes the interaction between the clay and the glaze doesn’t resemble the picture on the pint. What’s the solve? Test tiles in your different clay bodies. Make horizonal and vertical ones. Apply 2 coats on one side, and 3 coats on the other. Test. Test. Test. Test combinations. Test method of applications. Test. Did I say Test?

  • It ran. Was it a flux glaze meant to use on top or under another to make movement? Was it one of the beautiful metallic glazes? Did you put too many coats on? What’s the solve? Test.

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  • Pitting/pinholing. At DMS Ceramics, we fire twice which minimizes the chances of pin holing and pitting, but sometimes it happens anyway. Did you wipe off your bisque piece before glazing? Did you use too much glaze? Did you use a glaze notorious for pinholing? Is the glaze contaminated? What’s the solve? You can refire it in hopes that they will smooth out but this isn’t failsafe.

  • Glaze flaked off. This has to do with the way the glaze fits on the clay body. It happens when the glaze doesn’t have the expansion capacity to accommodate the glaze. What’s the solve? Without getting into glaze and clay chemistry and formulas, I would test all new glazes that I am unfamiliar with.
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    *When you refire your glaze piece, you risk glaze running and it could make bad glaze worse. However, it could also get rid of your pinholing and give your piece another chance with a different glaze treatment. I’ve refired several pieces because I hated the glaze and they’ve come out well.

Yes, it does seem like glaze issues are all about the clay, glaze, potential contaminants, and the method of application…but when is the (bad) glaze outcome the kiln’s fault? Excellent question!

  • When several glazed pieces come out matte instead of glossy . This is a symptom of under firing; the kiln didn’t reach temperature. What’s the solve? It’s possible that the kiln needs new elements or maintenance, but this rarely happens. Why? The DMS Firing Team uses Pyrometric Cones to measure the temperature inside of the kilns. We also check the digital temperatures on the outside of the kilns. If we have found that a kiln underfired, we typically notify the members and refire the load to temperature. Since I’ve been a member at DMS, this has maybe happened a handful of times and hasn’t been an issue.
  • When several pieces come out bloated . This is a symptom of overfiring. I’ve personally never seen this come from our kilns. In the teacher’s cabinet, there’s a shapeless burnt clump of low fire clay that looks like dried lava; this is a great example of overfiring. What’s the solve? Make sure that your clays and glazes are appropriate for our kilns. The Ceramics Wiki has info on what kind of stoneware and glazes you should get.

Tips:

  • Keep a glaze journal, it sounds dorky but really works!

  • If you don’t feel good about your glaze or your glaze job, wash it off (yes, you can wash glaze off your piece) and start over. Make sure to let it dry for 24 hours.

  • You can reglaze your glazed piece. Some potters use hairspray or sand down the glaze to help the newer glaze adhere to the surface.

  • When you get a fresh, new bag of clay that you aren’t familiar with, BEFORE you start to make art, make a bunch of test tiles. Use some of your favorite glazes on them and save some for a later date.

  • If you absolutely love a glaze, buy your own. We teach members hygiene practices when using community glazes but sometimes they contaminate them. They might dip the same brush in the two glazes or mistake the caps (I’ve done this once, accidentally of course and, personally witnessed another experienced member do this). They also might not rinse the brushes very well.

  • Ask for glaze recommendations via Talk. Our experience levels differ in time and breadth. Some of us thrive at the wheel, some of us thrive with glaze, etc. “I want a solid, stable blue to use on brown stoneware, does anyone have any recommendations?”


    Sources:

5 Glaze Defects and Expert Solutions for Fixing Them (ceramicartsnetwork.org)

7+Tips+for+Glazing+.pdf (squarespace.com)

How to Fix Pinholes in Your Pottery Glaze? — Spinning Pots | by Terry Connor | Medium

Glaze Pinholes, Pitting (digitalfire.com)

Can you Refire Underfired Glaze? – Rescuing Underfired Pottery (thepotterywheel.com)

Glaze Shivering (digitalfire.com)

How to Prevent Bloating in Your Clay Body - Ceramic Arts Network

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The first was a failure from the initial glaze test, the second was after the fix.

Left: One minute with a stick blender.
Right: Three+ minutes with a stick blender.

Otherwise, exactly the same clay body, firing schedule, timed dip application.

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Beautiful! Crystal producing glazes could get their own library of posts.
Stupid question- why a stick blender? Do you feel like it’s the best mixing tool?

Thank you!

Oooo, depends on the glaze and if I need to do multiple applications. Macro glazes have a lot of material that settles out so the stick blender can get down into that slurry at the bottom and pull it up into the mixture. I also really like the drill attached paint mixers for average to thin glazes as long as there is time for the bubbles to rise and disperse. If I am doing multiple applications, I like to do the initial mix with something powered to get a good blend but then switch to a whisk for between coats so I don’t froth it up.

You can get little battery powered mixers for using in jars but most commercial brushing glazes seem to do pretty well with just some stirring and bottle shaking. Lots of CMC gum!

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I am new to glazing and ceramics. This was soooo helpful. Thank you.

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