15 Tips to Get Started with Glaze Testing
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My Introduction To Glaze Testing
I find ceramic glazes to be absolutely fascinating. I had no idea when I started working with clay that glazes would become the main focus of my life.
My first year of pottery school was mainly about learning how clay worked and different ways of making different shapes. The focus was on form, function and skill-building, not so much on colour and aesthetics just yet.
Glazing was always an afterthought and I basically ruined most of my pieces by glazing them. In first year, we didn’t make our own glazes, we just used the studio glazes that were provided.
I didn’t have a clue what glazes were made of, how they were made or what happened to them in the kiln. And to be honest, I wasn’t all that interested. I just wanted to finally make something that looked how I imagined it should.
I was trying to be an artist. Somehow I ended up in art school which is the last place I would have imagined myself a few years prior. But life is funny like that.
Then came first semester of my second year. My very first glaze technology class. This was a major turning point in my life.
We finally learned to make glazes ourselves. We made a LOT of glazes ourselves. Collectively as a group, we made close to 1500 glaze tests. And this is when I really fell in love with ceramics.
First of all, wearing a respirator and weighing out powders using a triple beam balance scale made me feel super cool, like a scientist.
Yeah, I think scientists are cool!
The systematic testing that we did gave the right side of my brain a little break and lit up the left side of my brain that loves systems and calculations and data.
Math and chemistry were my best subjects in high school and even though I didn’t understand the chemistry of glazes yet, I felt like I was being taken back to my roots. Glaze testing felt really natural and I finally understood why someone like me ended up in art school.
That semester blew my mind. As a class, we first tested 128 different base recipes with multiple variations of each.
Then we each chose 2 base recipes and did “colour runs” with 45 different colourant tests for each base recipe.
One base recipe, 45 different colourant tests
Then, we each chose 9 colourant tests that we liked from each base and made these “glaze triangles” where we blended each glaze1:1 with every other glaze, resulting in 45 more glaze colours per base.
Colourant tests blended together
We had a lot of glaze cups and a lot of test tiles!
After taking that class, I was hooked on glaze testing. I loved trying new recipes and adding and removing ingredients to see what would happen. I would do lots of mini colour runs, testing just a few colourants with a base recipe to see how they reacted and whether I wanted to explore further.
I took lots of notes and photographs and spent countless hours staring at test tiles and recipes and coming up with new things I wanted to try.
I got to the point where I was more excited about test tiles coming out of the kiln than my own pottery. I made pots just to put glazes on them. And now, 10 years later, with thousands of tests behind me, I’m still just as curious and excited about glazes as ever.
The #1 Habit That Will Deepen Your Understanding of Glazes
After leaving school and putting together my home studio, I no longer had the luxury of glaze firings happening every few days. My glaze firings were often several weeks apart since I was making pots part-time and I was the only person filling my kiln.
Since my glaze firings weren’t very often, I made it a habit to put at least one test into every single glaze firing.
I didn’t want a glaze firing to go by without getting new information. I needed to seize each and every opportunity to try something new and see the results. Seeing results are the only way to learn and move forward.
This one little habit, multiplied by years of glaze firings has led to a much deeper understanding of how glaze materials work.
My #1 Habit: PUT A TEST IN EVERY GLAZE FIRING
We potters are so lucky that we can create our own glazes from scratch and have an infinite number of surface possibilities to choose from. The only thing that gets in our way is a lack of understanding of how our materials work and how to solve the problems that arise.
Developing a regular glaze testing habit is going to bring you closer to that deeper level of understanding with every firing.
I would love it if my story inspires you to make glaze testing a habit in your studio as well. I have some tips and ideas for you to get started down the glaze testing rabbit hole.
15 Tips to Get Started With Glaze Testing
If you’re like me and are fascinated by how glazes work, or you just want to understand glazes better so you can create unique surfaces for your pottery, here are some tips that will help you deepen your relationship with glazes and expand your palette.
1. Make lots of test tiles.
Make so many test tiles that you don’t think twice about using them. Test tiles can be any shape or size that you wish. They can be extruded, rolled as a slab, squished, thrown on the wheel, smooth, textured, you name it. It doesn’t matter how you make them, it just matters that you have them available and that you use them.
These are just some of the glaze tests I’ve done over the years
2. Make test tiles of every clay body that you use regularly.
Glazes will appear different and react differently to different clay bodies. When you’re testing a glaze, test it on multiple clay bodies if you can.
Testing colourants on 3 different clay bodies
3. Make test pots.
Test tiles tend to be small and only give a certain amount of information. It can be disappointing to find a glaze that you like on a little test tile and then glaze a whole piece with it and it looks completely different. I recommend making a bunch of test pots so you can see how glazes pool and run down vertical surfaces, etc.
To make test pots, choose a method that’s really fast so you can make lots and you’re not worried about wasting them. Make little bowls or cups or extruded cylinders. Test pots are great for filling in the spaces between other pots in your glaze firings.
I make lots of these small dishes and use them to test runny glazes
4. Buy some glaze testing cups with lids.
You can buy a sleeve of plastic drink cups, or I like to use small, clear plastic deli containers. They have flat lids so they can easily be stacked and stored.
I prefer the containers on the right over the cups on the left because they’re stackable
5. Test your current glazes at different thicknesses.
A good way to get started glaze testing is to take the glazes that you’re already using and try 1 second, 3 second, 6 second and 10 second dips, each on a separate test tile. Label them accordingly and fire them. You may get some interesting results with different thicknesses, depending on the glaze.
Make sure your glazes are mixed really well before dipping, and your kiln shelves are well protected in case your glaze runs.
Same glaze, different thicknesses
6. When dipping test tiles, make it a habit to always submerge the tile for the same amount of time.
For example, I always do a 6-second dip for test tiles. If I do more or less I’ll write it on the test tile for reference. This helps for consistency of results. The reason I do 6 seconds, which I consider long for dipping, is because a small test tile generally won’t absorb as much glaze as a large piece would. I want the test tile to be somewhat of an accurate representation of how the glaze would look on a piece.
7. Take a glaze recipe that you like, remove the colourant and test the base recipe on its own.
This will help you really see the glaze at its core, without being aesthetically influenced by its colour. Is it glossy or matte? Is it rough or smooth? Is it opaque or transparent? Does it have flecks and variation or is it uniform? Does it craze or not? Does it run or is it stable?
Then you can compare the base to how it looks with colourants and see how the colourant has affected the melt and surface texture. Colourants can change more than just the colour.
If you’re not sure which are the colourants, they’re typically copper, cobalt, iron, chrome, manganese, nickel, rutile, titanium, zircopax, tin and mason stains.
Same glaze, with and without colourants
8. Test the base recipe from tip #7 with different colourants.
Examples of colourants you could try are:
-
- 1-4% copper carbonate
- 1-10% red iron oxide
- 0.5-2% cobalt carbonate
- 5-10% mason stain
- 5-10% zircopax
There are more colourants, but those are the most common for when you’re just getting started.
Same glaze with different colourants
9. When you make a test glaze batch, make at least 200g
You can go smaller but smaller batches will be less accurate unless you have a scale that measures less than 1g increments (readability). If you have a scale with a readability of 0.1g or less then go ahead and make smaller batches. If the smallest measurement your scale will weigh is 1g, then you’ll get more accurate results with 200g batches.
Making 200g also gives you enough glaze to submerge your test tiles without hitting the bottom of the cup.
Of these three scales, the triple beam in the middle is the only one that will weigh less than 1 gram
10. If you want to test a few different colourants in one base, make a large batch of the base and then divide it into smaller test cups before adding colourants.
For example, if you want to test 5 different colourants, make 1000g of the base, mix and sieve the glaze and then divide it equally into 5 different test cups. This will give you approximately 200g of the base materials in each test cup. Then add the colourants as percentages of 200g.
I made 900g of the base and split it evenly into six cups of 150g each
Then I added different colourants to each cup
11. After you’ve tested different colourants in a base recipe, try blending them together.
This will give you new colours. For example, you could take a test containing 2% copper and mix it with a test containing 1% cobalt. As long as the batch sizes are equal, the resulting glaze will have 1% copper and 0.5% cobalt. You can find some gems this way.
12. PUT A GLAZE TEST IN EVERY FIRING
This is the #1 habit that will lead to a deeper understanding of your glazes.
13. Don’t forget to use witness cones in all your glaze firings.
You’d be surprised at what a difference a higher or lower temperature firing will make on your glaze results.
An example of a cone pack. I put at least one of these in every firing.
14. Take lots of notes and photos of your process and results.
Keep a glaze testing journal. Write everything down. You never know when the smallest detail can make a big difference. When you keep track of it all, you will start to connect the dots on which factors are influencing your results.
15. Have fun, experiment, be creative, try new things, follow your curiosity, enjoy the process.
Glaze testing makes unloading the kiln even more exciting. There’s something about coming up with a test you want to try, making it and then seeing the results that feels so empowering.
If you see glaze testing as a chore, you’re probably not going to do it very much. But if you see it as an exciting way to add a new level of creativity to the ceramics process, you’ll probably make some interesting discoveries.
Me in my respirator. Safety first!
I hope this post gave you some ideas for tests you can try. This is a very broad overview of ways to test glazes. If you have any questions or want me to go deeper on one of the tips, let me know in the comments.
No knowledge of chemistry is required to do this type of glaze testing. Once you’re hooked on glaze testing, there’s a whole wide world of chemistry to explore. The depth of knowledge you can reach is endless. I hope you’ll join me on the journey.
Do you already love glaze testing? What are some of your favourite tests or tips to share? Let me know in the comments. Do you have any kiln sitter tips to share? Please leave a comment below.
If this post helped or inspired you, please share it with others.
Download this blog post as a pdf
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Click here to get it!
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5 Ways You Can Make Your Glazes More Amazing (using glaze chemistry)
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Time: 10:00am Pacific / 1:00pm Eastern / 6:00pm UK time.
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This is a deep dive into all the chemistry that's happening inside the kiln.
Registration open Sep 21-29, 2023.
Learn to Mix Glazes from Scratch
If you’ve never mixed a glaze from scratch before and want to learn, I teach an online workshop called Glaze Mixing Essentials where I show you all the steps to mix a glaze and then test a base glaze with multiple colourants. Click the link for all the details.
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Always a great pleasure reading your posts, Sue. Looking forward to getting back into the studio and testing glazes!
Thanks Sue ! very clear and useful tips to follow. I am already starting this journey !
can this work with commercial glazes using different colour combinations and just seeing what they do? I dont have enough space for creating my own glazes yet, or any knowledge of it what aoever, so I currently use commercial glazes. Is there any books you might suggest to start the learning process of glaze making?
Yes, you can absolutely do a lot of glaze testing with commercial glazes. You can experiment by overlapping or even mixing together. You could test different thicknesses of application over and under other glazes.
Try a 1 second dip of Glaze A over and under a 1 second dip of Glaze B.
And then a 6 second dip of Glaze A over and under a 1 second dip of Glaze B.
And then a 6 second dip of Glaze A over and under a 6 second dip of Glaze B.
And vice versa with different glazes and different thicknesses. That sort of thing! The possibilities are endless. Test tiles are your friend. Take lots of notes.
Good luck,
Sue
Glad to hear it!
Sue
That’s great, Michael! Winter is a great time for glaze testing.
Sue
Thanks Sue, I love your blog and it’s amazing that you are sharing your knowledge with us???.
I’m so glad, thanks for letting me know!
Sue
Great post!!! I dream about having my own studio and doing tests just like this! Great ideas – just to test the base and then test different colorants, then mix the colorants together…. So many ideas and options to explore. Very interesting!!! Please keep sharing your glaze testing wisdom!!! — what affect, if any, do you find position in your kiln has? What kind of kiln do you use and what cone to you typically fire to?
Hi Nathan,
Every kiln is going to fire differently with hotter and cooler spots and it also depends on how tightly the kiln is packed. I have a couple of manual Skutt kilns at home and programmable Cone Arts and a Fredrickson front loader at work. Fire to cone 6.
Sue
I like to read you! Your writing skills make all this theory really enjoyable! Thank you so much for taking the time, I read everything you write!
Thanks so much, Krystel!
Thank you for sharing all your knowledge! When you mix 200g tests, do you sieve them with the same sieve you use to mix larger batches? It feels awfully big for getting into a tiny deli container… and what do you mix them with? You can’t fit the drill attachment in there?! do you just do it manually with a small whisk?
Hi Pam,
I have a small test sieve that fits right on the deli container. Google “Talisman test sieve” and you’ll see what I mean. And I use a hand blender/immersion blender, or a very small paint mixer attachment on a cordless drill to mix small batches. You’ll see it in the video on this post https://suemcleodceramics.com/how-to-measure-the-specific-gravity-of-your-glazes
Sue
Sue: Thanks for the advice !!! I have been testing but not organized like your tests. I’m loving !
Love you content! I’m curious what you do with all these small cups/containers of test glaze once you’ve run your tests? Do you dispose of the ones you choose not to use? Seems like the more testing you do the more you accumulate and I’m working in a small space and want to be efficient with my workflow. Thanks!
Thanks Sarah,
We have 2 mystery glaze buckets at the studio – a light and a dark – that I dump tests into when I’m finished working with them so they get used eventually. If you need to dispose of them, you can dry them out so they are lighter and easier to manage.
Sue
Thank you for your novice friendly style! Your straight forward plain language approach is less intimidating than some other resources. I never feel as though you are talking down to us. Makes me want to learn more!
Wonderful blog post Sue. I so want to test new glazes but I am one who finds it a chore! Your post helped me form a new approach so thank you.
One thing I struggle with is keeping notes and marking the test pieces. Could you someday share a bit on how you make your notes? I have tried paper and pencil and I have tried online recording but i never seem to get it right
Thanks
Have you seen my post called “What to Keep Track of in Your Glaze Journal”? That may help you. Or are you looking for a catalogue system? If so, I use Glazy.org to keep track of all my recipes and notes about my glazes.
Hi Sue! This is a great post and I’m excited to try this as I have recently discovered a base glaze that I really like.
One question – when you add the colorants to the small plastic cups, are you blending it in with an immersion blender? and do you sieve it again? or is it not worth the trouble for such a small batch?
Yes, I’m using an immersion blender and also sieving. Otherwise the colourants don’t become fully homogenized with the rest of the glaze. You want your small batches to be just as accurate as your large batches, otherwise when you scale up you may get a different result.
Thank you for this blog post Sue. I am gearing up to do glaze experiments and reading this was very informative and encouraging. I will make it a goal to do tests every time I run a glaze kiln for my high school students. I like the idea of just having an abundance of test tiles on hand. You also put Glazy.org on my radar, which will be helpful, because I stress when I can’t find my glaze notes.
Thanks again,
Bill
This was a really informative article. I am in my second year of art school and was petrified of making my own glazes. It was the subject that I enjoyed most!
The top for using small bowls rather than tiles is really good. Most of my glazes end up layered so runniness is a problem.