Glaze Management 101

It’s a lot of work to run a school or community pottery studio. There are a lot of moving parts to look after. I’ve been a studio technician since 2015 and it’s a very busy and rewarding job.

As the technician, I’m taking care of all the behind the scenes tasks that go into running the studio. These include firing the kilns, maintaining the kilns and other equipment, keeping the studio organized, ordering all clay and glaze materials, and of course, maintaining all the studio glazes.

Glaze maintenance can be a big job, especially if you have a lot of studio glazes and you’re mixing them from scratch. What size buckets to use? How to store them? What to use for mixing them? How to show users what the glazes look like?

You have to keep replenishing buckets that are running low. You have to replenish the water that evaporates from the glazes, which changes their thickness while leaving crusty glaze sludge on the sides of the bucket.

Sometimes lids are left off the buckets. Sometimes things are dropped into the buckets. Sometimes the buckets are accidentally dumped on the floor (usually containing red iron oxide, just to make clean up more challenging!)

If you have a lot of studio users and especially a lot of beginners, you’re going to have people who don’t mix the glaze quite well enough before dipping, which also changes the glaze’s water content. Dipping into a glaze that’s not mixed well leads to a higher proportion of water being removed from the bucket.

You need to make sure the glazes stay at a consistent thickness so you can give accurate instructions to the users and they can have consistent results. If your glaze thickness is always different, people can’t predict how the glaze will behave, which impedes their ability to improve their glazing. Adapting to a changing glaze bucket is a skill that can be learned but for beginners, it’s nice to have user-friendly glazes.

It can be challenging to stay on top of all these tasks if you don’t have systems in place to make sure it’s all getting done.

I’m going to share with you all the practices we use for our studio glazes and hopefully, you can adapt what we do to work for your studio.

We have 20 large buckets of glaze in our studio and around 250 users in our programs at any given time. We have 4 technicians on staff with at least one of us working every day of the week and we have a team of 6-10 volunteers who trade their services for studio time.

You may not have the time or resources to adopt all of our glaze management practices, but take what you can. Hopefully, you’ll learn a tip or two that will help you improve your routine and make the glazes better for everyone using them.

#1 – Buckets on Wheels

We use 5-gallon, 10-gallon and 20-gallon buckets in our studio. We mix 10,000g batches of glaze at a time and most glazes last 1-2 months before we need to make more. If you’re making smaller batches, you may use a smaller bucket size.

       

We keep our buckets on wheels in the studio so people can easily wheel them around without having to lift them. Some of our buckets, like the grey one shown above, come with special wheels that attach to the bottom. Some buckets, like the 5 gallon Home Depot buckets, sit on top of a rolling plant stand. It can support up to 500 lbs.

For the safety of users, I would suggest using wheels for any bucket of glaze that’s 5 gallons or larger.

If you’re using smaller buckets, get buckets with metal handles. Don’t use buckets with plastic handles. THEY WILL BREAK eventually. Guaranteed. Plastic breaks down over time so I would never trust a heavy bucket with a plastic handle.

Depending on what grade of plastic your bucket is made of, it will probably crack eventually too. Especially if the plastic flexes when lifting the bucket by the handle. You want a sturdy enough bucket that holds its shape when lifted. If it does flex, it’s better to hold the bucket by the bottom when carrying it. Keep an eye out for cracks forming near the rims and replace them before they crack completely.

When buckets are on wheels they last longer because they aren’t being lifted by the handle very often.

Note: Having buckets on wheels can make it easier to dump a glaze over, but the benefits outweigh the risks in my opinion. We have about two buckets spilled per year. Not a big deal, it happens!

#2 – Test Tiles on Buckets

We make flat, textured slab test tiles with holes in them to attach to the sides of the glaze buckets. Each glaze bucket has a tile of every clay body that we offer, dipped in that glaze and fired in both oxidation and reduction. For us, that’s 8 test tiles per bucket.

This helps users see how the glazes look different on different clay bodies and in different firing atmospheres.

The bucket test tiles are flat instead of L-shaped so they’re less awkward of a shape hanging off the bucket and less likely to break.

   

#3 – Test Tile Wall

We also have a wall of test tiles. Each test tile is first dipped in one studio glaze and then dipped in another glaze. So we have an example of every glaze over and under every other glaze in the studio. We have one set fired in oxidation and one for reduction.

The test tiles are numbered and we have a chart that shows you which glazes were used on each test tile. Each tile was first dipped in the glaze in the left column and then the bottom half was dipped in the glaze on the top row.

   

This test tile wall is a huge undertaking and not something you see in every pottery studio. It was not my idea, it already existed when I started working there. It’s great to be able to see how different glaze combinations look.

The main drawback of this amazing test tile wall is that results can vary so much, depending on the thickness of each glaze’s application. Sometimes there is disappointment when a piece doesn’t turn out like the test tile.

It’s important to communicate that the test tiles are just to give a general idea of a possibility and not a guaranteed result.

#4 – Hanging Glaze Mixing Sticks

We use large wooden dowels for our glaze mixing sticks. We also have a long-handled toilet brush that’s handy for scraping the glaze off the bottom since the wooden dowels aren’t great at that.

I would prefer it if our mixing sticks had more of a flat, paddle-like end that was better at moving the glaze around the bucket and scraping the sides and bottoms but this is what the studio has used for years and I haven’t had time to make any changes.

My biggest tip for mixing sticks is to have one stick designated for each bucket of glaze. A lot of time and water is saved when you can have a stick in each bucket that you’re using and you’re not having to rinse every time you switch glazes.

We label the sticks with the name of the glaze.

We don’t allow people to leave sticks in the buckets because the wood will rot. They have a loop on the end so they can be hung to dry on handy hooks under the table.

#5 – Monthly Glaze Sieving

Each of our glazes gets sieved every month. We have a chart to track when each glaze was sieved.

This is one of the main tasks that our volunteers help us with. First, they mix the glaze with a drill and paint mixer attachment. Then they pour the glaze through an 80 mesh sieve into another bucket. The sieve is a Talisman rotary sieve.

They scrape the main bucket to get all of the thick sludge and dried up, crusty glaze off the sides and back into the mix. The bucket is rinsed, the lid is cleaned and then the glaze is poured back through the 80 mesh sieve, into the main, clean bucket.

This keeps the glazes smooth and lump-free, makes sure they’re high-speed mixed on a regular basis, helps us remove the occasional foreign object from the bucket, and keeps the buckets and lids clean.

Dried up glaze on the side of a bucket turns to dust, which is a breathing hazard. We try to keep the studio free from dried up clay and glaze as much as possible.

#6 – Glaze Level and Thickness Monitoring

Since the technicians aren’t actively using the glazes, we rely on the users and volunteers to let us know when glazes are running low and if they seem thicker or thinner than usual.

We provide a whiteboard so users can tell us when glazes need attention. There’s a “Glazes running low” section and a “Glazes too thick/thin” section on the white board. People can write which glazes they want us to have a look at so we’re not running around checking the buckets all the time.

We suggest that they let us know before the glazes are too low to dip, so we have time to mix a new batch.

We don’t allow users to add water to glazes, that’s always the technician’s job. Otherwise, there can be a lot of conflicting opinions as to whether glazes need water or not.

Technicians have a system for determining if a glaze needs water, which requires no opinions. That system is called measuring specific gravity.

#7 – Monthly Specific Gravity Checks

Technicians measure and adjust the specific gravity of each new batch of glaze when it’s mixed, and we measure all the existing glazes every month to make sure the water level stays consistent. This promotes consistent application thickness for the users.

Since water evaporates and glazes aren’t always mixed to 100% homogeneity before dipping, it’s common for the water content to go down, and the glazes to thicken. By measuring and adjusting specific gravity, we make sure the water content stays the same.

   

When the water content is consistent, it’s easier for teachers to give glazing instructions and it’s easier for users to achieve consistent results.

If the water content fluctuates, then telling someone to hold their piece in for 3 seconds won’t always give the same result. If the glaze is too thick because water has evaporated, the glaze could run onto the kiln shelves, leading to disappointment for the maker AND the technician or volunteer who has to scrape the kiln shelf.

The best way we can control the glaze thickness for consistent application is to keep the water level consistent by measuring specific gravity.

If you don’t know how to measure specific gravity, please download my free guide with step-by-step instructions. There’s also a video of me measuring specific gravity in this blog post.

We have a chart to keep track of when each glaze was checked, much like the glaze sieving chart. We write the target specific gravity values for each individual glaze on the chart. We came to these numbers through testing and figuring out how each glaze works best.

Throughout the month, technicians chip away at measuring the specific gravity of all the glazes and mark the date on the chart.

#8 – Mix Glazes by Adding Dry to Wet

This tip comes from a safety perspective. As you probably know, most glaze materials contain silica dust, which is hazardous to our lungs. We must wear a respirator while working with these materials in their dry state.

Once the materials are added to water, they can no longer float in the air and into our lungs. For this reason, getting your glaze materials wet as soon as possible will reduce the amount of dust in your working environment.

When we mix a new glaze, we “add dry to wet” meaning we start with water in the bucket, weigh the dry materials and add them directly to the water, rather than the other way around where you add all the dry materials to the bucket and then add the water.

Adding dry to wet ensures the materials become wet right away and aren’t creating unnecessary dust clouds each time a new material is dumped into the bucket.

If you’re working in a shared space where others who aren’t wearing a respirator may walk into the room either during or after glaze mixing, you need to do everything you can to control how much dust is released into the atmosphere.

While this technique will reduce the amount of dust, it doesn’t eliminate it completely, so always wear proper PPE (personal protective equipment) while mixing glazes from scratch.

Note: When mixing glazes dry to wet, it’s important to add the clay (EPK, Ball clay, Bentonite) to the water FIRST so the other materials don’t hard-pan on the bottom of the bucket.

#9 – Test Each New Glaze Batch

When we mix a new batch of glaze, before we add it to the old batch, we fire a test tile to make sure the glaze was made correctly.

99% of the time, it’s great and we dump it straight into the main bucket. For those occasional mishaps, we have the opportunity to find our mistake and correct it if possible without contaminating the existing bucket of glaze.

#10 – Record When New Glaze Material Bags are Opened

Every time we open a fresh bag of a glaze material, we mark down the date and the amount. The dates and amounts are added to a spreadsheet that totals how much of each material we’ve used over time and gives us a monthly average for each.

I keep the monthly averages on my inventory sheet so I can easily compare how much we have left to how much we typically use each month.

This helps me with ordering because we don’t have much space for extra materials and we don’t want to run out of anything either.

Since I place a monthly order for clay and glaze materials, I can easily see at a glance whether we’re likely to run out of something soon, or if we have enough for a few months and I don’t need to re-stock just yet.

#11 – Record the Quantities and Costs for Each Glaze Batch

We have a glaze mixing sheet for each of our glazes. Each sheet has the recipe written out with percentages and then columns for each batch that we make.

When we want to make 10,000g of a glaze, we batch it out on the sheet by multiplying each material percentage by 100 to see how many grams we need to add to the bucket.

We keep track of the quantity of each glaze that we make over time. This helps us calculate our glaze costs per month, based on how much material we’re using as opposed to how much material we’re ordering that may not be used right away.

You can input the costs of your glaze materials on Glazy.org and it will calculate the cost of all your glaze recipes. The software takes your material costs and multiplies the cost by the percentage of that material in your glaze recipe. This way you can see how much a batch of each of your glazes actually costs, whether it’s 1000g or 10,000g.

It can be eye-opening to compare the costs of different glazes. Since material costs vary so much, some glazes are way more expensive to make than others. If you’re trying to cut studio costs, you may want to replace some of the more expensive glazes with cheaper ones.

Recording the quantities of each glaze we’re making also helps us to see which glazes are the most popular and which glazes don’t get used very often. We can use this info to decide which glazes to keep and which glazes we might want to replace with new ones.

#12 – No Outside Glazes Allowed in the Studio

The last tip is a policy that we have at our studio. The users are required to use the glazes we provide for them. We don’t allow them to bring in outside glazes, whether they’re commercial or made from scratch.

This is to protect our kilns, kiln shelves and other people’s pots from unexpected glaze running. Regardless of whether it’s a “tried and true” glaze or a commercial glaze rated for our temperature, we simply can’t take the risk of firing glazes that we haven’t tested.

Considering how busy our studio is, we don’t have time to test glazes for anyone. I would love it if that was my job, to test glazes for people, but it’s not feasible at our studio. We have to be able to offer the same service to everyone, so it’s just a hard “no” every time.

Having a policy like this keeps the kilns clean because we always know exactly what’s being fired in them. We also don’t allow outside clay bodies, all clay must be purchased at the studio.

We offer 20 different glazes, plus stains and coloured slips that can be layered and combined in an infinite number of ways so studio users are encouraged to get creative when they become bored of what we have to offer.

A Lot of Glaze to Manage

So there you have my 12 tips for managing glazes at a busy pottery studio. I certainly don’t do all of this in my home studio. It’s easier to keep track of glazes when there’s just one person using them.

I definitely do the specific gravity checks though, every time I glaze.

Here’s a summary:

#1 – Buckets on wheels

#2 – Test tiles on buckets

#3 – Test tile wall

#4 – Hanging glaze mixing sticks

#5 – Monthly glaze sieving

#6 – Glaze level and thickness monitoring

#7 – Monthly specific gravity checks

#8 – Mix glazes by adding dry to wet

#9 – Test each new glaze batch

#10 – Record when new glaze material bags are opened

#11 – Record the quantities and costs for each glaze batch

#12 – No outside glazes allowed in the studio

I hope you found this valuable whether you manage the glazes at a busy studio or not. It’s always interesting to see how other people do things in other studios.

I’d love to hear your own tips for how you manage the glazes at your studio. Leave a comment below to let me know what you do differently.

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