Glaze Chemistry 101: A Quick Course on How To Make and Test Your Own Custom Ceramic Glazes

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Remember, in high school chemistry class when you found yourself thinking, “when will I EVER use this stuff in my life?” (unless, of course, you always dreamed of becoming a chemist). Well, if you became a potter, chances are you have found yourself getting reacquainted with some of the terminology from high school chemistry. If the glaze chemistry bug hasn’t bitten you yet, it probably will eventually as you’ll want to customize your work with a particular glaze surface. Learning how different materials contribute to glazes and clay bodies is very important in expanding your abilities as a ceramic artist.

So, in today’s post, we are presenting a little intro to glaze mixing and testing from Richard Zakin. In it he explains how the glaze making process is easily mastered if you have the right tools, follow an ordered procedure, and take the work seriously. Take it away, Richard. – Jennifer Harnetty, editor.


Ceramic Glaze Making

For most ceramists the first experience of the technical side of ceramics takes place during glaze making. The process of glaze making is easily mastered if you have the right tools, follow an ordered procedure, and take the work seriously.


You Will Need

  • An accurate scale calibrated in grams.
  • A clean pan or bucket in which to weigh the glaze materials (your scale may come with such a pan). This is called the measuring container. Stainless steel salad bowls come in various sizes and make excellent measuring containers.
  • A clean bucket in which to mix the weighed glaze materials.
    This mixing container must be large enough to hold the entire recipe.
  • A good dust mask (with government safety approval).
  • Water (for suspending the glaze).
  • A fine sieve, either 50 or 80 mesh (50 or 80 strands to the inch).
  • If you are making up a large amount of glaze (more than 2,000 grams) you will also need a coarse sieve (the type you can buy in the supermarket).
  • A clean bristle brush (for pushing glaze through the sieve).
  • A waterproof marker (for labeling the glaze container).

 

The Ceramic Glaze Making Process

  • Glaze tests by Richard Zakin.

    Put on the dust mask.

  • Locate each material in your recipe and make sure you have enough of it.
  • Clean the scale and make sure it’s properly balanced before you begin work.
  • Place the measuring container for weighing your materials on the scale. With no materials in the container, the indicated weight should be set at zero point. If not, adjust the tare compensation of the scale so that it reads zero.
  • Weigh your first material.
  • Place it in the container that you will use to mix and store the glaze.
  • Weigh out each successive material and place it in the mixing container.
  • Add enough water to make a mixture the thickness of cream.
  • If you have a propeller mixer, use it at this point. Otherwise, mix the glaze with a stirring stick or a wire whisk. Once the glaze is properly mixed with water, you may remove your mask.
  • Place a sieve supported by two sticks on top of another mixing container.
  • Pass the glaze mixture through the sieve (you can use a stiff brush to force the glaze through the sieve). This homogenizes the mixture and gets rid of any lumps. If you have made up a large amount of glaze (more than 2,000 grams) it greatly speeds up the process to pass the mixture through a coarse sieve before using the fine sieve.
  • Move the sieve over to the original mixing container and pour the glaze through the sieve once more. Double sieving insures a smooth mixture.
  • Make a waterproof label for the glaze and place it on the container.

 

Ceramic Glaze Testing

Unlike paint, glazes must be fired. Furthermore, glazes are transformed by the fire and do not have the same surface or color before they are fired as after. The kiln firing changes the characteristics of the glaze in a most profound way. The best way to track these transformations is to fire glazes first on a test tile. This will allow you to see what a glaze’s surface, color, and texture are after firing. The test tile should be fairly large and should have a character that is similar to your normal work. It is especially important to use the same clay and firing as you normally use in your work. Both of these strongly influence the character of the glaze.

Glaze tests by Angelo diPetta.

The Ceramic Glaze Testing Process

  • Prepare a test tile.
  • Thin the glaze with water to the appropriate consistency. For single color application this is liable to be the thickness of heavy cream. If you plan to use the glaze in a multiple-layer glazing strategy, the glaze (or glazes) should be thin and milky.
  • Apply the glaze to the tile by dipping, pouring, or spraying.
  • Fire the tile in a way consistent with your normal firing methods.
  • Label the completed glaze test. Include its name, recipe (including colorants), firing cone, and the date. In a classroom or group situation include your initials for identification.

 


**First published in February 2010
Comments
  • Richard is the best! His knowledge, skill and his wonderful kindness is a great gift to the world of ceramic art!

  • Very cool, good basics. I HATE it when I screw up and forget to label something! I keep a glaze book for the tests too, and notes about each. This really helps especially when going back over the years of testing to try to pull something new together.

  • There are so many recipes, but this is the first time I’ve heard the actual process explained in detailed steps.Makes it seem much easier!

  • I recommend brushing a stripe of a contrasting color of slip or underglaze on each tile before bisquing the tile. This will tell how opaque or translucent a new glaze is by how clearly the stripe shows through after firing.

  • I use a fine brush dipped in water and Iron oxide (6:1 ratio) a ceramic pencil is good also, to write a code number on the bottom or back of my tiles as how many times have I lost labels or forgotten what test was what!

  • I also recommend painting a stripe of iron oxide and/or cobalt carb horizontally on top of the applied glaze to see if the glaze moves or not. It will also tell you if the one or two colors influence or are influenced by the basic glaze. I also suggest you have an indent from a stamp to show edges.

  • I like to “sift” the dry ingredients using the sieve first then after the water use the sieve again, I have found the glaze seems to mix so much easier and far less lumps, if any. I don’t know why but it works for me. Of course you need to wear your mask a little longer.

  • I’m used to mixing paints (red and yellow make orange) i wish there was a easy way to mix comercial underglazes so you would have a general idea what color will come out

  • If you have a controller on your electric kiln the firing cycle is very important. I’m finding very different effects on a few of my glazes when I slow down the cooling. It seems to be essential to do this to get a matte or semi-matte surface. Some of the articles I read in the popular magazines suggest firing cycles. Does anyone know of a real thorough treatment of this?

  • I am going to mix my first glaze this week end. So this detailed process has arrived in my mail box just in time. Easy to follow and easy to understand. I was going to work from notes from a Ceramics book, but was getting quiet nervous about the procedure. After reading this, feeling a little more confident. Thanks Richard.

  • I agree with Cornia on sifting the dry ingredients first. Makes it a whole lot easier. Kind of like in baking, sifting ingredients first helps avoid lump.
    For testing, I like the throw tiny saki cups off the hump and then make some marks on the inside. This way I am able to see how the glazes breaks on raised and indented designs, translucency as it runs down and how it will pools. I try to make these really thin so they aren’t to heavy write what glaze it is on the outside with watered down iron oxide. Though I haven’t down it yet, they can be glued to a board as reference. for now I just keep them in a little box.

  • Great article. To get a little more out of my test tiles I create a matrix on each tile. Picture a 3 x 3 tic-tac-toe grid on a bent tile with a grooved facet. Across the top row is one coat of glaze, across the middle, two coats and across the bottom row three coats.

    After the third initial coat, down the left hand column I brush texturizer. The middle row is left unaltered and the right hand column is brushed over with a gloss-clear glaze.

    Since I routinely use both red and white (low fire earthenenware) clay I repeat this for both clays. Now I see 18 possible effects for each glaze, greatly expanding my options.

    Mike Koch
    Klaytivity.com

  • I put a small amount of water in the container I’m going to mix and store the glaze in before I weigh and add any materials. It cuts down a lot on the dust that rises up when you tip the materials in, especially with the very light, fine materials. The more dust I can keep out of the air in my work space, the better as far as I’m concerned.
    If there are favorite glazes you mix and use often, or a glaze that doesn’t store well wet, the weighed materials can go into a plastic bag,(labeled!), and sealed. Once the bag is sealed, the materials can be tumbled together before being added to water, which is especially helpful if the glaze contains bentonite as a suspender. Dry batches don’t take up a lot of room, and they’re ready to add to water and mix whenever you need them. I hate getting excited about glazing a bunch of work, only to discover I’m running short on a particular glaze!

  • I am still learning and have soooo many questions. I was told it is best to let a newly mixed glaze sit at least 24 hours and then sieve a second time, then use it. Any thoughts? A good thing or a waste of time?
    Col

  • Actually, if you let it sit overnight before you seive it, it gives the materials a chance to get thoroughly wetted, which can mean it mixes smoothly and without lumps, making seiving easier. (Just as plaster mixes smoothly if it has time to get thoroughly wetted first, but tends to be a lumpy disaster if you skip that bit.)

  • See also the indispensable “Ceramic Spectrum” by Robin Hopper for an exhaustive description of glaze testing and a very efficient coding method! It’s the best money I ever spent on a ceramic reference.

  • Working strictly from knowledge gained with commercial glazes, I see 4 very vital pieces of info missing (never know what they will uncover = 12ish tiles)

    1: make 3 test tiles – fire all 3 once, 2 twice and 1 three times. Sometimes the color will change with successive.
    Had a specialty glaze came out a beautiful sky blue. added some details and refired – it had grass green splotches on it. The final coat the piece turned green.

    2. make 3 test tiles – coat all once, two twice, and 1 three times. See if there is a difference in color with multiple coats. You HAVE NOT LIVED unitl you make a Cherry red Pegasus, and have it come out a beautiful light blue with streaks of red in it.
    experimentation showed that the difference was coats – one coat was light blue, two was red streaked blue, 3 was cherry red.

    3. “Fire as per normal process” other than the overglazes, our shop fired all colors at the same cone (and oxy level). Reading magazines – the reason Red is so hard to get is it needs to be low-fired. The reason it took so many firings to get black nice – it needs to be high-fired. At least the brand they were selling did.
    Since I did not have my own kiln, I could not experiment beyond adding some red to the overglaze pieces – worked out much better.

    4. Alternate your oxy level – anoxic, normal, high octane. This is the secret of the Greek red/black pieces. You fire them anoxic, the piece turns black. you take it out and overglaze what you want to stay black, then refire with normal oxygen – the black will turn red.

    Someday we will have the space and money to start playing again… and then it’s going to be FUN!!

  • also make log of how various media interact – Duncan Autumn Gold over snow makes the absolutely most beautiful, multi-faceted moss green you will EVER find.

  • All great to read, but I was wondering if you have any suggestions for high-fire glazes, and by this, I mean recipes, especifically. I live in Quito,Ecuador and am having a hard time because I always worked with low-fire and at the studio where I work they only do high-fire. So far, the pieces I’ve fired have not come out the way I expected!! Thanks a lot for any tips….. Pia

  • Terry, you’re talking about ‘anoxi’, normal, and high octane. Are you firing with fossil fuel ?? Confusing, because I’m firing cone 6 electric, and those words ‘don’t compute’ with any of my firing experiences. Please explain ? Thank you.

  • The easiest way I found to keep track of glaze test fires is to carve numbers on the bottom of the test tile and keep detailed records in a journal. Works for me.

  • no, not firing temps at all. Amount of Oxygen available within the firing chamber, determined by completely closing, completely opening or partially opening the peepholes…or at least that’s how the one doing the experiment did it.
    The Annoxic or low oxygen content caused the black glaze; when they returned it to normal oxy content, the black glaze turned red.

  • I’m beginner in clay art. I just know something. I have an electric kiln with precise computing control temperature. Do I need to know about using cones? If yes, how to hand make them? Because, until now I have fired clay keeping slow temperature. Thank you.

  • Zvonko – cones are basically your temp guides. They tell you ‘the oven is now at 350º, it is safe to put the cookies in’.
    Some glazes are low, reg and high cone – low, reg and high temp – and results will differ with the wrong temp.

    how to make them by hand could be an intersting article by itself!

  • kenny

    I add no more than a teaspoonfull of dry glaze to my porridge…seems to make no difference in the taste…I’m studying gastrological consequences of the practice…so far, so good…anyone else tried this?

  • Rather than a tile, I prefer a test ring. It can have a flat surface at the top and vertical sides that can give you an idea of how the glaze runs. Being a ring, it is easy to insert a strip of thin card with all necessary notes on it and staple the ends together on the outside. Finally, being holes, the test rings can be strung together in related groups or just suspended from somewhere.

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