Reading this page will help you learn new terms for glazing/firing.
You can understand their meaning used in context with images to help.
Links to reference videos are provided to help gain further knowledge on specific processes.
Kahoot quizzes at the end of the first section, glazing, will help you assess your understanding of glaze testing percentages.
An interactive crossword at the bottom of this page will help you assess your understanding of these new terms.
You can understand their meaning used in context with images to help.
Links to reference videos are provided to help gain further knowledge on specific processes.
Kahoot quizzes at the end of the first section, glazing, will help you assess your understanding of glaze testing percentages.
An interactive crossword at the bottom of this page will help you assess your understanding of these new terms.
If you haven't already done so, visit the Tools Page to learn about some glazing/firing Tools used in Ceramics, then play the Matching Game to connect the Glazing and Firing tools to their definition
Glazing
Glazing is only one form of decoration, (as seen on the Decoration Page ) but perhaps the most popular. Glazing produces an impervious glass like surface.Glazes can be sprayed, poured or dipped. Layering different glazes together can achieve interesting results.
Reference VideoAlthough you don't need to watch these to complete the quizzes on this site, they are a great way to further your understanding.
Watch this YouTube video on How to Glaze Pottery! Tips, Tricks, and Techniques by Jonthepotter
https://www.youtube.com/watch?v=9y12CCHq74s |
Glazes can be bought ready made, or made using a glaze recipe where powdered glaze ingredients are added to water and sieved. Glaze recipes can be adjusted or created and testing new glazes is important to see how they perform. Small test tiles are a great way to try variations of a glaze, or see how it performs at different temperatures.
Health and Safety
Glaze materials can be dangerous
Masks should be worn so as not to breathe in powdered materials
Surfaces should be wiped down with a wet cloth
Hands should be washed after contact with glaze
No eating/drinking in case of ingesting glaze powder
Some glaze chemicals are harmful enough to have warning symbols on labels and should be kept in locked cupboards
Glaze materials can be dangerous
Masks should be worn so as not to breathe in powdered materials
Surfaces should be wiped down with a wet cloth
Hands should be washed after contact with glaze
No eating/drinking in case of ingesting glaze powder
Some glaze chemicals are harmful enough to have warning symbols on labels and should be kept in locked cupboards
Weighing dry ingredients
Normally (but not always) glaze recipies will be written so that the ingredients add up to approx 100 grams dry weight (with or without colourants)
This makes it easy when doing the maths to increase your glaze recipe to larger quantities
For example- times each glaze ingredient in a 100g recipe by 5 and you get a 500g recipe. If it weighs more/less, a mistake has been spotted before glazing.
This is where most glaze mistakes are made as wrong quantities are added by not doing sums first and ticking off measurements as they are made.
Once an understanding of glazes and what the ingredients do has been built up, glazes can be altered to change their qualities (opacity/runniness/colour etc)
Normally (but not always) glaze recipies will be written so that the ingredients add up to approx 100 grams dry weight (with or without colourants)
This makes it easy when doing the maths to increase your glaze recipe to larger quantities
For example- times each glaze ingredient in a 100g recipe by 5 and you get a 500g recipe. If it weighs more/less, a mistake has been spotted before glazing.
This is where most glaze mistakes are made as wrong quantities are added by not doing sums first and ticking off measurements as they are made.
Once an understanding of glazes and what the ingredients do has been built up, glazes can be altered to change their qualities (opacity/runniness/colour etc)
Additions
Students often start experimenting with glaze recipes by making test tiles with set variations to the colourants added.
A Biaxial blend (or line blend) uses only two colourants producing a single line of test tiles, this example uses 20% increments of colourants.
As you can see each tile has 100% colourant amount, which has been added to the same base glaze;
Tile 1: 100% A
Tile 2: 80% A + 20% B
Tile 3: 60% A + 40% B
Tile 4: 40% A + 60% B
Tile 5: 20% A + 80% B
Tile 6: 100% B
Usually colourants are tested in 10% or 20% increments, when smaller increments are tested, more test tiles are produced giving more information.
It is important to number the backs of the test tiles with red iron oxide dissolved in water so as to know which tiles are which.
Students often start experimenting with glaze recipes by making test tiles with set variations to the colourants added.
A Biaxial blend (or line blend) uses only two colourants producing a single line of test tiles, this example uses 20% increments of colourants.
As you can see each tile has 100% colourant amount, which has been added to the same base glaze;
Tile 1: 100% A
Tile 2: 80% A + 20% B
Tile 3: 60% A + 40% B
Tile 4: 40% A + 60% B
Tile 5: 20% A + 80% B
Tile 6: 100% B
Usually colourants are tested in 10% or 20% increments, when smaller increments are tested, more test tiles are produced giving more information.
It is important to number the backs of the test tiles with red iron oxide dissolved in water so as to know which tiles are which.
Triaxial blending is when three colorants are chosen, and blends of these colourants are tested (in a base glaze)
e.g. one test tile may have 20% of colourant A , 60% colourant B , 20% colourant C , while another tile is 100% colourant A. If all variations are tested a triangle of test tile results can be produced and used to refer to when choosing. |
Try this Kahoot on Biaxial line blends, and then this more complicated Kahoot on Triaxial blends.
Find the correct set of missing percentages to see if you have understood.
Find the correct set of missing percentages to see if you have understood.
Firing Temperatures and types
Clays and glazes mature at different temperatures. Underfired clay will not be as strong , overfired clay can bloat (bubble) warp and melt, underfired glaze may not have melted enough and be dry or rough, overfired glaze might run off the form. Understanding the chemistry of the materials involved can help you alter them to suite your requirements, such as altering the recipe to fire at a lower temperature, or to alter the colour, or to understand why it didnt come out of the kiln looking how you expected and how to correct it.
A device called a Thermocouple is used to know the temperature inside the kiln, Pyrometric Cones gauge the Heatwork (combined effect of temperature and time) by melting and bending over within the kiln. They are normally placed in threes , one that melts at the temperature required , one for the next lower temp, and one for the next higher temperature, so you can tell if the firing is underfired or overfired. Cones are viewed through a Bunghole (peephole) they help to decide when work has been fired fully. You can refer to this cone chart http://www.porcelainpainters.com/conechrt.htm for more information. The difference in Heatwork (time and temperature) is shown to effect the final temperature at which the cones bend (visible in the two columns for the senior cones).
Some kilns have a kiln sitter in which a cone is placed, when the cone is reached, the kiln turns off automatically. Bungs (Stoppers) are left out of the Bunghole until the kiln has reached 600°C to allow evaporated water to leave the kiln , this also avoids water damage to kiln elements in an electric kiln, at 600°C Bungs are put in the Bunghole to keep heat inside the kiln., but can be removed temporarily to view the Cones.
A device called a Thermocouple is used to know the temperature inside the kiln, Pyrometric Cones gauge the Heatwork (combined effect of temperature and time) by melting and bending over within the kiln. They are normally placed in threes , one that melts at the temperature required , one for the next lower temp, and one for the next higher temperature, so you can tell if the firing is underfired or overfired. Cones are viewed through a Bunghole (peephole) they help to decide when work has been fired fully. You can refer to this cone chart http://www.porcelainpainters.com/conechrt.htm for more information. The difference in Heatwork (time and temperature) is shown to effect the final temperature at which the cones bend (visible in the two columns for the senior cones).
Some kilns have a kiln sitter in which a cone is placed, when the cone is reached, the kiln turns off automatically. Bungs (Stoppers) are left out of the Bunghole until the kiln has reached 600°C to allow evaporated water to leave the kiln , this also avoids water damage to kiln elements in an electric kiln, at 600°C Bungs are put in the Bunghole to keep heat inside the kiln., but can be removed temporarily to view the Cones.
Greenware is unfired dry clay and can be recycled.
Ceramic is Clay that has been fired high enough that it can no longer be recycled into wet clay.
Bisque Firing - A first firing , typically 1000°C, that is followed by a subsequent glaze firing. Some ceramicists will "once fire" work but this comes with more risk.
Silica Inversion - this occurs during firings. It is the changing of the structure of Silica molecules (during Quartz phase at 573°C / Christobalite phase at 225°C) which causes expansion and contraction and can cause stress within the form requiring a slower firing through these temperatures.
Earthenware - Low fired usually under 1200°C, with high porosity (Porous)and a separate glaze layer over the body. You might think of terracotta flowerpots as an example.
Stoneware - High fired usually above 1200°C, with low porosity (Not Porous) and an integration of the glaze and the body. You might think of a porcelain vase as an example.
Earthenware and Stoneware are used to describe the firings and also the clay and glazes that work at those temperatures and the ceramics produced by them.
(Earthenware clay/ an Earthenware glaze/ an Earthenware firing / Earthenware Ceramics)
Clays like porcelain are low in impurities , they are dug from the mountains, clays like terracotta have alot of impurities, they are more likely to have been transported by rivers and picked up other elements along the way which lowers the firing temperature. There is alot of Iron in Terracotta which gives it its colour. Alterations can also be made to the clay body, Grog ,fired clay which has been ground up, can be added to wet clay to reduce shrinking/ add texture/reduce warping.
Ceramic is Clay that has been fired high enough that it can no longer be recycled into wet clay.
Bisque Firing - A first firing , typically 1000°C, that is followed by a subsequent glaze firing. Some ceramicists will "once fire" work but this comes with more risk.
Silica Inversion - this occurs during firings. It is the changing of the structure of Silica molecules (during Quartz phase at 573°C / Christobalite phase at 225°C) which causes expansion and contraction and can cause stress within the form requiring a slower firing through these temperatures.
Earthenware - Low fired usually under 1200°C, with high porosity (Porous)and a separate glaze layer over the body. You might think of terracotta flowerpots as an example.
Stoneware - High fired usually above 1200°C, with low porosity (Not Porous) and an integration of the glaze and the body. You might think of a porcelain vase as an example.
Earthenware and Stoneware are used to describe the firings and also the clay and glazes that work at those temperatures and the ceramics produced by them.
(Earthenware clay/ an Earthenware glaze/ an Earthenware firing / Earthenware Ceramics)
Clays like porcelain are low in impurities , they are dug from the mountains, clays like terracotta have alot of impurities, they are more likely to have been transported by rivers and picked up other elements along the way which lowers the firing temperature. There is alot of Iron in Terracotta which gives it its colour. Alterations can also be made to the clay body, Grog ,fired clay which has been ground up, can be added to wet clay to reduce shrinking/ add texture/reduce warping.
Most of my pieces are glazed, I have specialised in reduction glazes, I like the boldness of colour, which is multi-dimensional and varied. Other firings give different finishes and not all firings require glazing. I am now using my own electric kiln and oxidation glazes.
Reduction Firing - The reduction kiln, is used to reduce the oxygen in the kiln during firing, this affects the colours that can be achieved (copper in an electric kiln is blue/green while a gas reduction kiln is often used by people hoping to achieve the elusive copper red). This is because in a reduced atmosphere the lack of oxygen inside the kiln means that the oxygen within the glaze is drawn out. Reduction kilns are typically fuel burning kilns (gas) as reduction firings can damage an electric kiln.
Oxidation firing - Electric kilns give more consistent results, and slightly different colour ranges. Oxidation firings can be done in fuel burning kilns as well as electric.
Reduction Firing - The reduction kiln, is used to reduce the oxygen in the kiln during firing, this affects the colours that can be achieved (copper in an electric kiln is blue/green while a gas reduction kiln is often used by people hoping to achieve the elusive copper red). This is because in a reduced atmosphere the lack of oxygen inside the kiln means that the oxygen within the glaze is drawn out. Reduction kilns are typically fuel burning kilns (gas) as reduction firings can damage an electric kiln.
Oxidation firing - Electric kilns give more consistent results, and slightly different colour ranges. Oxidation firings can be done in fuel burning kilns as well as electric.
Crystalline Glaze Firing - Control of firing temperatures is needed to allows for crystal forming in certain glazes, including slow cooling rates.
Raku Firing - The Raku Hybrid was first fired to Bisque in an electric kiln , glazed, then fired a second time, in a gas fuelled raku kiln. Raku firing is done at a lower temperature , and instead of allowing work to cool down in the kiln, it is taken out while hot, and so cooled quickly in the air.
Pieces can also be sprayed or submerged in water while hot, or placed in combustible material like wood shavings or sawdust, this has a localised reaction similar to the gas kilns reduction firing, which has produced the red flashes on the copper in these pieces.
Smoke Firing - This Terracotta Hybrid was Bisque fired in an electric kiln, warmed in a raku kiln and taken out while hot to smoke fire straight away. All pieces were smoke fired in metal bins using wood shavings and newspapers.
It not been glazed and areas of shine are from burnishing and use of Terra Sigillata. (very fine slip)
Raku Firing - The Raku Hybrid was first fired to Bisque in an electric kiln , glazed, then fired a second time, in a gas fuelled raku kiln. Raku firing is done at a lower temperature , and instead of allowing work to cool down in the kiln, it is taken out while hot, and so cooled quickly in the air.
Pieces can also be sprayed or submerged in water while hot, or placed in combustible material like wood shavings or sawdust, this has a localised reaction similar to the gas kilns reduction firing, which has produced the red flashes on the copper in these pieces.
Smoke Firing - This Terracotta Hybrid was Bisque fired in an electric kiln, warmed in a raku kiln and taken out while hot to smoke fire straight away. All pieces were smoke fired in metal bins using wood shavings and newspapers.
It not been glazed and areas of shine are from burnishing and use of Terra Sigillata. (very fine slip)
Another type of smoke firing is a Pit firing it is an outdoor firing in a hole filled with combustible material and left overnight to smoke. Low fired Porous ceramics take on designs from the smoke absorbed and reactions with combustibles including organic materials and colourants.
Saggar Firing - This skull was Bisque fired first in an electric kiln, then fired a second time in ceramic boxes called saggars inside an outdoor gas kiln. Each of the Saggars I used contained wood shavings. Smooth areas have been burnished before firing and some pieces are highlighted with graphite after firing. Saggar firings can also be done by wrapping work in aluminium foil or newspaper or even raw clay (see video) ,with combustible material between the work and the saggar, and placing the wrapped items in an outdoor gas kiln or pit firing. How much of the ceramic is covered determines where and how much smoke is absorbed.
Reference VideosAlthough you don't need to watch these to complete the quizzes on this site, they are a great way to further your understanding.
Saggar and Raku Firing - Alternative Techniques by Dale Van Houzen
https://www.youtube.com/watch?v=ZPtureW_cKo Ceramic Review: Masterclass with Jane White by Ceramic Review . As well as showing Pit Firing this video also revisits many of the processes we have looked at on this page.
https://www.youtube.com/watch?v=5OS2Zsw6FgU&t=246s |
What have you learnt ?
- Tools used in glazing and firing
- Health and Safety
- Increasing the volume of Glaze Recipes
- Biaxial and Triaxial blending
- Firing Temperatures and types
- Glazing and Firing Vocabulary
- Health and Safety
- Increasing the volume of Glaze Recipes
- Biaxial and Triaxial blending
- Firing Temperatures and types
- Glazing and Firing Vocabulary
Hopefully this will have given you a basic understanding of some of the processes in Ceramics, and a glossary of terms to describe them.
Can you remember what these terms mean ? If there are some you don't know go back and take a second look.
Can you remember what these terms mean ? If there are some you don't know go back and take a second look.
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Here is a link to some more ceramic terms by the V & A , which you may also find useful https://www.vam.ac.uk/articles/a-z-of-ceramics
Can you use your new knowledge and vocabulary to identify details about ceramic pieces.
Visit the Quiz Page now.
Use the wordsearch, Quizlet flashcards and games to help you, remember repetition aids learning.
Then fill in the missing words in the ceramic descriptions of processes and glazing/firing.
You should then be ready to identify processes that have been used just by viewing a photograph of a ceramic piece, take the quiz to see how well you do.
Visit the Quiz Page now.
Use the wordsearch, Quizlet flashcards and games to help you, remember repetition aids learning.
Then fill in the missing words in the ceramic descriptions of processes and glazing/firing.
You should then be ready to identify processes that have been used just by viewing a photograph of a ceramic piece, take the quiz to see how well you do.