Experimenting with ceramic glaze recipes is one of the most interesting and important ways to learn about ceramic materials! But the chemistry of glaze chemistry can be an overwhelming subject. That’s why we have a large part of the ceramic arts network dedicated to ceramic glaze recipes. Here you will find everything from raku glaze recipes with low fire to glaze recipes with high heat for use in the wood kin!
Learning how different materials contribute to glazes and clay bodies is very important for developing your ceramic artist skills. In the Glaze Chemistry section, we have compiled several articles and information about Glaze Chemistry to help you understand this incredibly complex and fascinating topic. The best way to learn more about ceramic enamel recipes and how the materials influence each other is through testing. Look for these items, go to the studio and take the test!
Contrary to what was once prevalent, low fire glazing do not mean boring results. Today, some of the best ceramics are produced at low temperatures. To explore this temperature range, refer to the Recipes for low heat glazes section of the Ceramic Arts Network. You will find a whole range of information on the production and use of low fire glazes recipe, from textured to matt and from majolica to transparent glossy glazes. As always, you will also see colorful pictures of finished works that have been glazed with these low fire glaze recipes.
Medium range firing is probably the most popular firing range today, as the results are excellent and more environmentally friendly than high fire. In the “Mid-range glaze recipes” section,
Many potters and ceramics artist choose to fire in the high fire range, as this gives the most vital and long lasting results. And most of the artists who fire to this range mix their own glazes. And many of them are looking at the Ceramic Arts Network’s High Glaze Recipes section to find new recipes for ceramic glazes! Here you will find not only a collection of recipes for high fire glazes, but also information on firing methods and techniques in the range of high fire temperatures.
If you’re like me, mentioning the word chemistry can panic you – it’s certainly not my favorite subject. But I love ceramics, so it became clear to me some time ago that I had to face my fears and familiarize myself with the chemistry of ceramics.
Yes, a general knowledge of ceramic chemistry and glazing materials can be very helpful when mixing glazes and interpreting firing results.
Ceramic Chemistry – The Elements
The elements are forged in a star in central ovens. Ordinary stars like the sun burn hydrogen, two atoms of hydrogen collide to form one atom of helium and release energy in the form of heat and light. Dying stars lack hydrogen and helium atoms fuse to form the heaviest elements. Heavier elements of iron, such as lead and uranium, only form when a massive star explodes and becomes a supernova. The dust that remains after such an explosion eventually forms again and forms new stars and planets like our Earth. We are literally made of star dust.
In ancient times, it was believed that the basic elements or components of the material were earth, air, fire and water. We now know that there are actually more than 90 elements found in nature, including metals, semi-metals and non-metals. At ambient temperature, some elements exist in the form of gas, others in liquid form and many in solid form, but their state of matter can change with temperature. As potters, we are more interested in the elements of the earth’s crust that form stones, because these are also the elements present in clay and enamels. The most common are oxygen, silicon and aluminum, followed by iron, calcium, sodium, potassium and magnesium (1).
Ceramic Chemistry – The Potter’s Periodic Table
The periodic table describes the chemical and physical properties of the various materials used by potters. It is the basis for understanding chemistry as a whole. However, we are very interested in the elements useful for potters, which include silicon, aluminum, the alkali metals and alkali earth metals, as well as the transition metals.
In the nineteenth century, scientists noticed that groups of elements had similar properties. Not all elements have been discovered yet, but if they were arranged in seven layers in order of increasing atomic number, a similarity between the groups became apparent. We now know because all the elements in a group have the same number of electrons in the outer shell, so they all react in the same way.
In the periodic table, the elements are listed in ascending order of the ordinal numbers. There are seven rows of elements and eighteen columns. The elements in each column, referred to as a group, have similar properties. Important groups for ceramics are group 1, the alkali metals (sodium, potassium, etc.) and group 2, the ground alkali metals (calcium, magnesium, etc.). These are used as flux in glazes. All elements on the left and in the middle of the periodic table are metals. The lower ones are called heavy metals because they have more protons and neutrons and therefore more atomic weights. Many of the metals found from the early nineteenth century have names ending with “-ium”, for example sodium, calcium, barium. Their oxides forms alkaline solutions when dissolved in water. Oxides and not metals are of great interest to the potters because they are made of clay and glazes.
The center block of the periodic table contains transition metals. These can have various oxidation states and are important for producing colored glazes, especially metals along the top row: chromium, manganese, iron, cobalt, nickel, and copper. The two rows inserted at the bottom are known as lanthanides and actinides, and some can also produce colors in glass and glazes. Uranium is the heaviest natural element and can produce yellow in glazes, although it is no longer used due to its radioactivity. Elements beyond uranium can only be synthesized in nuclear reactors and radioactively decomposed to other elements. Lead is the most stable non-radioactive element.
To the right of the periodic table is a diagonal line that separates metals from non-metals. The elements on this line include boron, silicon and arsenic. They are known as metalloids and are semiconductors, which means that they only conduct electricity under certain conditions. Silicon is the basis of modern electronics and computers. Some of the most useful elements for potters are also on or near this dividing line and include silicon and boron, both of which are glass formers, although the latter is primarily used as a flux in low temperature glazes and in heat-resistant borosilicate glass. In addition to silicon, aluminum is contained in clay and is used as a stabilizer in glazes, which means that it does not become too liquid when fired. On the right side of silicon is phosphorus, which is used as a flux in glazes and porcelain. Antimony and selenium are used in small amounts as yellow and red dyes in glazes.
The upper right corner of the periodic table contains oxygen, the halogens fluorine and chlorine and the noble gases helium and neon. Oxygen is present in all clays and glazes, usually combined with silicon and aluminum as oxides. Fluorine is of interest to the potter because it is often released in the oven by decomposing fluor fir, a mineral found in Cornwall Stone.
The far left of the periodic table is very alkaline and the right is very acidic. The strength of the alkali decreases from side to side, while the strength of the acid increases. For example, in the third row sodium oxide (Na 2 O) is very alkaline, magnesium oxide (MgO) is alkaline, aluminum oxide (Al 2 O 3) is amphoteric, silicon dioxide (SiO 2) is acidic and phosphorus pentoxide (P2O 5) is very acidic. In ceramic glazes and glass-like ceramic clay bodies, the alkaline and acidic oxides react with one another and melt. The alkali metal oxides are fluxes that react with the acidic glass former silicon dioxide. The elements in the central block are amphoteric (can react as acid or base / alkali), although many have slightly alkaline or acidic properties. Their oxides are used in glazes as additional fluxes, stabilizers, opacifiers and dyes.
High Fire Glazes
These are glazes that I find useful for my work, and I will continue to add the list if time permits, and as I discover more. Some glazes are from recipes from books or online, and I have tried to list the source where I can. Many glazes are later modified by me as I adapt them to my use and the materials I have in my part of the world.
All glazes should be tested before using them on something important. Your kiln, your clay, your glazing materials, your scales, your water, the thickness on which you apply your glazes and your firing schedule are different from mine, and all that makes a difference in the end result!
I tried to list the glazes according to colour. This is of course not satisfactory because it is possible to use glazes for other colors as well, but it is a start!
I often put one glaze over another, all sorts of interesting inter-mixtures as a result of this, and because there are so many variables in terms of glaze thickness and what glaze goes over what, it is difficult to ever get two pots quite the same as each other with this method.
Two underglazes that I use frequently are both by the New Zealand potter, Len Castle, and are to be found near the back of a glorious book that was published in 2002 by Sang Architects and Company Limited to celebrate Len’s work called, “Len Castle Potter”.
These glazes can be fired in oxidation or reduction.
Len Castle underglaze 1 Cone 9 -11
Potash feldpar 24
Ball clay 3
Red iron oxide 6
This is a very dark brown and fairly static satin glaze at cone 10.
Len Castle underglaze 2 Cone 9 -11
Mixed or potash feldspar 50
Red iron oxide 9.5
Cobalt carbonate 0.5
This is more fluid than underglaze 1 and is nearly black
These are dark brown to black glazes that usually “break” to a straw colour, mid brown, or iron red where they are thin. I have two that I use quite a bit in the electric kiln, and I “inherited” them from my teacher, Peter Watson, when I started potting. I use these glazes on their own or under other glazes.
I have fired these in oxidation and in reduction. If anything my results were darker and nicer in my electric kiln. In my wood fired kiln the glazes were not as dark, and were a little “muddy”, and I do wonder if the wood ash in the atmosphere tended to bleach out the iron somewhat??
Black Tenmoku Cone 10 – 11
China Clay 10, (I used Ball Clay)
Potash Feldspar 55, (I use Nephaline Syenite if I want the glaze to mature at around cone 9 – 10, ball clay in place of china clay also helps with this)
and red iron oxide 8.
Red Tenmoku Cone 9-10
Potash Feldspar 50
China Clay 10
Red Iron Oxide 8
This glaze worked well in my wood fired kiln, and was good in my electric kiln. In the wood fired kiln, the clay body had more influence on the appearance of the glaze.
A28 Orton cone 10
Potash feldspar 33
washed wood ash 40
standard borax frit 5
This was my own attempt at a “nuka” style glaze.
The real thing is mostly made from rice straw ash, but East Otago New Zealand is not a great rice growing area, so an alternative needed to be found. This works well in oxidation and reduction, has an interesting flecked appearance due to the wood ash, and is also good over underglazes such as the Len Castle underglazes that I have shown above.
Magnesium Matt Glazes
I have only fired this one in my electric kiln, but suspect it would work well in reduction.
Buttermilk Orton cone 10
Potash Feldspar 29.3 (the recipe says Custer Feldspar but we don’t have that in our part of the world).
Gerstley Borate 10.5 (I still have some of this, but you could use Gillespie Borate or another substitute)
The glaze base is a white glaze that is in John Britt’s Cone 10 Glaze book (The Complete Guide to High-Fire Glazes).
The glaze has an attractive texture something like an egg shell, but whiter and a touch more shiny. The glaze is nice on its own, but I had a hunch that it would make a nice cobalt violet, because the glaze contains quite a lot of magnesium, and magnesium and cobalt tend to produce purple, or violet. I really like this variation.
An excellent book entitled “The New Potter’s Companion” by Tony Birks lists some useful stoneware glazes. A matt Dolomite enamel bears the mysterious name “BNO”. It has confused me for years about the meaning of this name, but Nigel Graham wrote a comment on this glossy page to let me know that “BNO is short for” Brian’s Nice Oatmeal “, a recipe that Brian Newman used to study over the years has developed 60 “. So, thanks Brian for the clarification.
I put the BNO in my electric oven and my wood oven, both with good results.
BNO, 1250 ° C oxidized (2282 ° F). Source, Tony Birks, “New Potter’s Companion”.
Cornish Stone 50
Chinese tone 25
It is a beautiful enamel that I found useful in the past, both for oxidation in my electric oven and for cooking wood. The glaze felt soft like an eggshell. Then something happened to my Cornish stone … not only did the price in my part of the world become prohibitive, but the material itself changed and became fireproof and less interesting for the enamel. I was looking for a replacement. I tried replacing potassium feldspar or soda feldpar with Cornish Stone directly, and it didn’t work as well as the original. With the help of the Insight Glaze software from digitalfire.com, I became more adventurous. Attempts to make a perfect substitution where the theoretical formula was the same resulted in an enamel that melted … only … but looked “thin” and full of tone. After my intuition and doubling the amount of soda feldspar in my replacement, it gave me good coverage, which may not be the BNO I liked a few years ago, but it is a coverage that seems useful.
My BNO, cone 9-10
Soda feldspar 23.8
Potassium feldspar 9.5
Chinese tone 26
I have only fired PTM and Bailey’s Red in my electric kiln thus far, but the Janet DeBoos Iron Red has worked well both in electric and wood firings, with wood firing being the best of all.
PTM Probably best fired to Orton cone 9.
Potash Feldspar 41
Ball Clay 13
Bone Ash 13
Red Iron Oxide 10
+ Dolomite 11
+ Lithium Carbonate 2
What I like about PTM, is it is a little “wild”. It moves and changes colour as it goes from thick to thin. Throwing rings show up well, and close to, or under magnification, the colour is very complex, showing flashes of plum, tomato, blue, orange, and brown. At time of writing I have only ever fired this in an electric kiln. If fired too high, or put on too thickly, the glaze can pool in an unattractive brownish puddle in the bottom of a bowl or cup.
Note that with iron reds it is well worth experimenting with slow cooling. A hold of about 45 minutes at 950 degrees Centigrade (1742 F) allows time for the iron to re-oxidise and iron crystals to grow. A better, stronger red can be gained this way.
This is for oxidation firings.
Green/blue Orton cone 10
Potash feldspar 8
Soda feldspar 8
China Clay 16
Bone Ash 4
Tin Oxide 2
Copper Carbonate 1
This green/blue glaze is one that I developed recently. It is a substitute for one that is in a Thames and Hudson glaze book (The Glaze Book A Visual Catalogue of Decorative Ceramic Glazes by Stephen Murfitt).
Here is the glaze from the Thames and Hudson glaze book that I based my own glaze on. This glaze is listed as being for 1290 degrees C or 2354 degrees F with an hour soak.
Cornish Stone 28
China Clay 12
Bone Ash 4
Tin Oxide 2
Copper Carbonate 1
I love the look of the glaze in the book, it’s a green that shades through to clear on rims and edges. The glaze goes crazy, but it makes it attractive. There’s a watery clarity in the glaze that reminds me of a cold copper-colored pool on the mountains. The original glaze uses Cornish stone and this is a very expensive glaze ingredient in this part of the world. As much as I like them, I can’t afford to use them in quantities other than small quantities. I chose an alternative. Unfortunately, the weight of potassium feldspar cannot simply be replaced by the weight of Cornish Stone, since they are completely different materials. You have to attack on several fronts at the same time! I turned on the Insight brushing software that I had recently bought and felt until I chemically had something very similar to the original paint, but I used soda and potash feldspar instead of the Cornish stone and matched the other ingredients in the glaze to both Chinese clay as well as silica had to be increased significantly.
When I tried the glaze on a tile, I found that, to my surprise, my replacement was much better than the original, and provided excellent coverage when applied with a brush (the extra china clay in my replacement would help). The color was almost identical, just like the madness. This is a frosting with character, and I suspect it will work well as copper red when rotated in reduction, but I haven’t had a chance to try it yet. At cone 10, the glaze moves and glows attractively at the bottom of the bowls, creating a blue color when it is dense, green where it is medium, and almost bright when it is thin. It is not really suitable for the type of potter where everything has to be the same, but it is a nice addition to my glaze repertoire.
Low Fire Glaze Recipes
You can make a full rainbow of pottery glazes for your projects. Low-fire temperatures allow the use of colorants that would burn off or become unstable at higher temperatures. These low-fire glaze recipes are arranged from a lower temperature to higher, with the firing range given in cones. The percentages given in these recipes are by weight, not by volume. Your glaze batches should be mixed using distilled water. Whenever you are trying out a new glaze, make small batches and test them.
Note that this glaze does not add up to 100 percent. Rather, it is using the old “parts” system where parts, or portions, are of equal weight.
Curdle Blue, Cone 012-09
Use caution, as these are poisonous raw materials.