How To Mix a Ceramic Glaze From Scratch

 
A red iron oxide glaze in the process of being run through a Talisman Glaze Sieve.

A red iron oxide glaze in the process of being run through a Talisman Glaze Sieve.

 

This post is an overview of how to mix a ceramic glaze from dry ingredients, including the tools, techniques and procedures to get you started.

Whether you buy a pre-mixed dry glaze or weigh each ingredient, there are a lot of advantages to mixing your own glaze:

  • Save money: Mixing glazes in your studio is always cheaper, sometimes as much as 80 to 90 percent cheaper than bottled glaze.

  • Customize: Learn how to modify slips and glazes to suit your kiln and clay bodies.

  • Learn glaze chemistry: Even a bit of info can help you get the results you want.

A variety of our favorite glaze recipes are posted here, and there are lots of websites and books with glaze recipes. There are endless amounts of glaze recipes, so if you are new to this, just start with one basic one such as a glossy clear. There are also pre-mixed, dry glazes which are effective and still save some money over buying bottled glazes.

Keep reading for the complete how to instructions.

Table of Contents

  • Glaze Mixing Tools and Accessories

  • How To Mix Glazes From Scratch

  • Testing and Storing Glazes

  • Summary

Glaze Mixing Tools and Accessories

Here’s what you need to mix glaze in your studio:

How To Mix Glazes From Scratch

  1. Review recipe.

    Check to make sure you have enough of each ingredient. It can be helpful to calculate and write out the amount of each material, to be used as a checklist.

  2. Prepare work area

    Put on a dust mask, clean your scale and work area. Get your materials, buckets, and scoops together.

  3. Zero scale

    Place your measuring pan or bowl on the scale and turn it on. If needed, press the tare button so that the scale is zeroed out.

  4. Weigh ingredients

    Weigh each ingredient (this is where your checklist is handy) and put them in a dry bowl or bucket. After measuring all the ingredients, mix the dry ingredients together. Some glaze ingredients, such as bentonite, are prone to clumping so it is important to mix everything dry first.

  5. Add to water and mix

    Add the mixed glaze materials to water and mix until it is thick cream or buttermilk consistency. An electric drill with a proper mixing blade greatly speeds up this process. A large plastic scraper will dislodge material from the side of the bucket. Once all the dry ingredients have been mixed with water, you can remove your mask if desired.

    Note: it’s best to add glaze materials to water. If you add water to a bucket of dry materials, it’s hard to get everything in the bottom corners mixed.

  6. Sieve and homogenize

    Prepare another clean bucket with a sieve, preferably a fine 80 mesh sieve. Run the glaze through the sieve this first time, to break up any clumps. A brush can help push material through the sieve, or a Talisman Glaze Sieve is a tool made specifically for mixing glaze into 5 or 10 gallon buckets.

    Then, clean the bucket where you will be storing the glaze. Run the glaze through the sieve a second time into this clean bucket.

  7. Test glaze consistency

    Glazes are typically mixed to a specific gravity, which measures the amount of dissolved solids in the water. Usually glazes are around 1.50, which means 50 parts dissolved solids to 100 parts water. Keep records and mix the glaze to a consistency that works for you.

    Specific gravity can be measured with a specialized (but fragile) hydrometer, or you can use a graduated cylinder on your scale. With your cylinder zeroed out on the scale, pour in 100ml of the mixed glaze and check the weight. Add water as needed, and mix.

  8. Label and store

    Glaze containers and lids should be labeled with the name, temperature, and any other information that will help you. Laminated, waterproof labels are best but packing tape can also protect a label for some time.

Testing and Storing Glazes

Testing Glaze

It is helping to make a test tile of a glaze, on each clay body you use. Vertical test tiles such as tubes from an extruder are best, as they show how a glaze will “move” with gravity. Dip your test tile with one and two dips to show how different thicknesses of glaze affect the color.

Some studios choose to make a test tile with each batch of glaze. But if you are careful to mix the glaze accurately to a similar specific gravity, and your firings are repeatable, you should get roughly the same glaze results each time. There are no guarantees with glaze though. It is important to keep records, both in a glaze book and a kiln log, in order to get standardized results. But, glaze materials do change over time so as necessary you can make new test tiles.

Storing glazes

Glazes can be stored in sealed containers or buckets almost indefinitely. Most glaze ingredients are inorganic and will not rot. But some ingredients, such as bone ash, can cause some rotting smells. To avoid this, make sure the glaze is mixed with some frequency. If the odor persists, you can add a trace amount of copper to any glaze (even white glazes!) without affecting the color. Copper is an anti-fungal and can cut down or eliminate odor. Read our post on that here.

Remixing glaze

As they are used, glazes do lose some moisture to evaporation and bisqueware can suck extra water out of the glaze mix. It can be helpful to mix and then do a quick visual check of the glaze. If necessary, you can re-check the specific gravity and add water. If a glaze seems thick or is glopping onto your pieces, it’s definitely time to check it and probably add water.

In addition, when I mix glaze, I will usually run all the old and new glaze through a sieve. Small bits of bisque and other contaminants can fall into a glaze bucket. When I’m using it, I want to know what I’ve got in that bucket. It does take extra work but having a double-sieved, homogenized glaze will result more even glaze application and hopefully, better results.

Summary

This post has covered a basic overview of mixing glazes from scratch. It covered the tools, techniques, and a few helpful hints to mix and store glazes. If you can follow a recipe, you can mix glaze. There is an overwhelming amount of glaze info out there, but if you start with just one basic recipe and grow from there, you will be a glaze master in no time and you will be able to customize and mix glazes to suit your own needs.

If you are looking for more info on mixing glazes, the glaze books by John Britt are some of the best resources.

The Complete Guide to Mid-Range Glazes

Buy at Bookshop.org

Buy at Amazon

The Complete Guide to High-Fire Glazes

Buy at Bookshop.org

Buy at Amazon

Questions or comments? Let us know in the comments.

The Best Way to Eliminate Odor from a Stinky Ceramic Slop or Glaze Bucket

Updated and revised, September 9, 2023

A dirty, stinky throwing slop trash can in need of some cleaning and copper carbonate, to eliminate odors.

A dirty, stinky throwing slop trash can in need of some cleaning and copper carbonate, to eliminate odors.

Stinky slop and glaze buckets can be a problem in any ceramic studio. The smells range from a swampy, pond-mud smell to a very strong sulfurous odor. All are caused by some kind of organic matter in your clay or glaze.

In addition, some glaze materials such as bone ash or CMC are organic materials and will start to smell over time, especially if the bucket is not stirred regularly.

To deal with smelly buckets, the best practices are to:

  1. Keep organic materials like brush bristles, paper, etc out of your buckets and jars

  2. Stir and mix your materials more frequently

  3. Cycle materials more frequently

  4. Clean your buckets with soap and water, and sterilize them with bleach

Adding bleach? In some studios, bleach is added to slop buckets or clean up buckets and mixed with the clay slop. This is an ok thing to do, but has it’s drawbacks. Usually, the bleach will just mask whatever the problem is for a few days or weeks, and then the smell will return. And I personally don’t like to add bleach to buckets where the material is being recycled such as clay slop buckets. And if you add too much bleach, the slop water can be rough on your hands.

The following article covers some ideas for eliminating odors from glaze buckets, underglaze jars, and slop buckets. Discussed is a somewhat extreme method of adding copper carbonate. In general, I would use this as a last resort after you have tried to cycle material, or clean outed and sterilized the problematic bucket. A little bit of copper can get rid of smells, because of the antimicrobial properties of the element, but using it does have some drawbacks as well.

This practice of adding a small amount of copper carbonate comes from a tip I read many years ago I read in Ceramics Monthly. (I haven’t been able to find the link) The tip from the potter was adding a trace amount of copper carbonate to glaze buckets. My memory is just a gram or two. It wasn’t enough to change the color of the glaze (even in a white glaze), but it was enough to prevent mold growth. If you have a glaze that regularly smells, try adding an extremely small amount of copper carbonate to any glaze, and see if that fixes the problem. The tutorial below also covers adding copper carbonate to slop buckets, in addition to some strategies to deal with smell glaze and underglaze jars.

Table of Contents

  1. How To Eliminate Odor From Glaze Buckets

  2. How To Eliminate Odor from Underglaze Jars

  3. Maintaining and Dealing with Odor in Slop Buckets and Reclaim Clay

How To Eliminate Odor From Glaze Buckets

Stinky glaze buckets happen from time to time. Usually, this is caused by some sort of organic matter. It could also be caused by organic glaze materials such as bone ash or CMC gum. For bone ash glazes, try stirring the glaze more often, or proceed with the copper carbonate fix as detailed below. For glazes with CMC gum, try replacing that with bentonite, which is a very fine, inorganic clay that can help glazes stay in suspension.

Before adding copper carbonate to a stinky bucket, screen the glaze first to make sure you’ve removed any brush bristles, bisque chunks, or other foreign matter. Sometimes, just stirring the glaze more often may eliminate the issue, so try that first!

Method:

Add 1 gram of copper carbonate per 5 gallons of glaze, stir, and wait 24 hours.

That’s it!

Just a bit of copper should take care of the problem, and in such a small amount, it shouldn’t change the color of the glaze. I even did this once with 5 gallon bucket of white glaze. A little risky, but it worked without changing the glaze color.

If you are nervous about adding copper carb, or if your studio scale is not very accurate, try measuring the smallest amount you can, such as 2 or 5 or 10 grams, and then physically dividing it up to get down to something like .5 grams or 1 grams, and add that small amount to your glaze. If the smell isn’t gone in 24 hours, repeat the process.

If the copper carbonate doesn’t solve your problem, don’t keep adding it past 2 or 3 grams. Eventually, you will add enough to alter the color of the glaze. If the problem persists, you may have to discard the glaze and start over with a fresh batch.

How to Eliminate Odor from Underglaze Jars

Underglaze jars can get really stinky. Some in particular, such as the various reds from the Amaco Velvet Underglaze line, seem prone to getting stinky.

To prevent odors with underglazes:
> Remove any cardboard liner from the caps
> Stir to mix. Don’t shake all the underglaze against these cardboard liners
> Try to prevent brush bristles from dropping in
> Keep any other organic matter out of the jar

But if your underglaze gets stinky? There may not be much you can do. It’s such a small volume, and our best remedy, copper carbonate, is a colorant. Still, you can try adding a very small amount of copper, approximately 1 gram or less. Stir into your underglaze, cap it up, and wait 24 hours. Check and repeat if necessary. Caution: you will change the color of your underglaze if you add copper to them! I’ve done this a few times with the extremely-prone-to-stinkiness Bright Red Velvet Underglaze. The copper mutes the red a bit, but it’s actually a lovely result that is still red.

But the conclusion is, there may not be much you can do for a stinky underglaze except to tolerate it and/or discard and buy a new jar.

Maintaining and Dealing With Odor in Slop Clay Bucket

A slop bucket is a great way to reduce the amount of clay going into your sink and can also be used for initial cleaning of splash pans and throwing buckets. If there was room, I’d have a series of three of these for cleanup. But in the studio I manage, there is just one 40 gallon trash can with a mesh lid. It’s used to collect all the throwing slop.

Ideally, this trash can gets completely emptied about once a month and the heavier slop is saved and mixed with reclaim clay. But while the slop is building up, the bucket can get pretty stinky. And if you recycle stinky slop, then you have stinky reclaim clay (although the process of mixing does seem to help alleviate some problems with smell.)

The first step I would take with a stinky slop bucket would be to completely empty it and clean with soap. Then, sterilize the bucket or trash can with bleach and let it dry completely. Usually this will eliminate your stinky slop bucket problem for at least a few months up to 6 months. Slop buckets will always get smelly at some point so just plan to fully clean and sterilize it on a regular schedule.

A more extreme solution is adding a small but regular dose of copper carbonate to your slop bucket. Caution: adding copper carbonate to reclaim clay may result in small green spots showing up through white or clear glazes as you are adding copper to your clay! Use this method at your own risk.

The tutorial below covers maintaining a slop bucket with copper. As mentioned, try cycling your materials more regularly, keep organic material out of your bucket, and give your bucket a deep clean before trying this method!:

Step 1: Remove water, add copper carb, and stir

Ideally, the slop bucket is a settling tank so that heavier clay particles will separate and fall to the bottom. Pictured here is a 40 gallon trash can. As the can fills to the top and settles, pull off the top 10 gallons of water. This watery slip goes down the sink in my studio, but you could choose to let it settle and then decant.

After taking off the top 10 gallons, add about a half a spoonful of copper carbonate. This is about 2-3 grams of copper carbonate.

After adding the copper carbonate, stir or mix the whole slop bucket with a drill. It helps to disperse the copper.

Add about 1/2 spoonful of copper carbonate per approximately 20-30 gallons of slop.

Add about 2 to 3 grams (about 1/2 spoonful) of copper carbonate per approximately 20-30 gallons of slop.

Copper carbonate on the surface, ready to be mixed into the slop.

Copper carbonate on the surface, ready to be mixed into the slop.

Step 2: Clean the Lid

A clean lid for our slop bucket.

A clean lid for our slop bucket.

Not exactly necessary, but a regular lid cleaning makes it easier to maintain and inspires respect from your fellow studio mates.

It’s a bit hard to see in the picture, but I am are using my favorite pro-grade cleanup sponges.

For the lid on our bucket has a DIY screen made by cutting a hole in the trash can lid and attaching rubberized mesh with nuts and washers. The mesh helps to keep tools, sponges, and large chunks of clay out of the slop bucket.

 

Step 3: Repeat as Necessary

Our bucket with a clean lid and a bit of copper to prevent any stinky odors.

Our bucket with a clean lid and a bit of copper to prevent any stinky odors.

As stated above, it takes us approximately 1 month to end up with about 15 gallons of heavy slip but usually every week or more often, I remove the top layer of watery slip from the bucket. Every time water is removed, I add copper to the bucket.

Once there is 15 gallons or so of heavier slop at the bottom of the bucket, I remove it and put it in 5 gallon “settling tanks,” This watery slop is then poured over dried out scraps or added to the pugmill as needed. It’s the best way I can think of to capture all the fine particles left over from the throwing process. I’ve also found that as this slop with copper moves through the reclaim process, it combines with other clay and helps keep that reclaim from getting stinky too.

Occasionally, I do notice a little green copper speck popping into a white glaze from the reclaim clay, so if you want to be extra careful, use the least amount of copper necessary, or mix it into a watery slurry before adding to your slop bucket.

Summary

This post has covered a variety of ways to deal with smelly glaze, underglaze, and slop buckets. Also detailed is how to use copper carbonate to eliminate odor in glaze buckets, underglaze jars, and slop buckets. It’s an effective and affordable way to manage the inevitable odors that arise in a ceramic studio.

Do you have any other techniques for maintaining odor-free slop and glaze buckets? Let us know in the comments.

Shop materials and tools mentioned in this post: