Getting started with mixing your own glazes can be daunting. There’s a lot to consider and the wealth of materials, methods and recipes can be overwhelming. Fortunately, many have walked the same path and can guide you through your first batch of tests. We’re going to help make a satin/matte glaze and a glossy glaze in a variety of colours with the minimum amount of work. Once you’ve fired them, you will be able to see how they look on your clay body, put there with your hand in your kiln - which could be very different from other people’s test tiles.
We’re going to end up with 42 test tiles! But don’t panic, it won’t take as long as you think
The first surprise of glaze mixing is that it doesn’t take much to switch from matte to glossy using the same five or six materials in different proportions. So we’re going to pick a couple of very different looking glazes with almost the same materials, so that we can minimise the things we have to buy and manage when first starting out. You can make a huge variety of glazes with just six things, one from each line:
- Silica - usually from quartz or flint. They can be interchanged freely
- Clay - usually Kaolin. Kaolins vary slightly, and are often listed as EPK (a specific type of Kaolin), but can usually be swapped without trouble. I use Cornish China Clay. Ball clay has a different chemistry. In addition to silica, clays contain alumina.
- Feldspar - Potash, Soda or Nepheline Syenite. Feldspars contain similar materials to clay, but with the addition of potassium and soda. Different feldspars have these materials in different proportions. If a recipe has a specific feldspar (for example, Custer Feldspar) then it can be substituted for another in the same class, in this case a different Potash Feldspar.
- Calcium - Whiting or Wollastonite. Wollastonite contains both calcium and silica.
- Magnesium - Talc or Dolomite. In addition to magnesium, talc contains silica as well. Dolomite contains calcium.
- Boron - a Frit (for example ferro frit 3134) or Gerstley/Gillespie borate. Gillespie Borate is a man made version of Gerstley Borate, which is no longer available. The two GBs are equivalent.
Other common ingredients include zinc oxide, strontium carbonate and lithium carbonate.
We’re going to add some colourants to a couple of glazes and mix them together to produce a large range of colours and effects, which will teach you about how these colourants work and what kinds of effects you can get with them. We’ll need a total of 11 different materials; 6 for making the glazes and 5 for adding colour and effects.
Picking a base glaze ‘starter pack’
Glazes without colourants are called base glazes. Sometimes they’re designed that way, but any glaze can be used as a base by simply removing the colourants.
The first step is to pick a pair of base glazes that are made with similar materials. The following examples are for Cone 6, but the technique will work equally well at any temperature. They are typical and reliable cone 6 glazes. Feel free to pick two other glazes with any materials you like. Which you pick will depend on how other people’s tests look, what materials you can buy, how much you like the name and blind luck. That’s how glazing works. Methodical luck.
Starter pack 1
- Custer/Potash Feldspar
- Frit 3134
Starter pack 2
- Nepheline Syenite
- Gerstley Borate
Starter pack 3
- Custer/Potash Feldspar
- Gerstley/Gillespie Borate
- Zinc Oxide
Starter pack 4
This pair only requires 5 materials, because the matte is a type know as a calcium matte it does not require magnesium (talc or dolomite). You will need to be able to ‘slow cool’ your kiln to use this starter pack.
Glossy: Zam celadon
Matte: G1214Z Satin
- Nepheline Syenite
- Frit 3124
Starter pack 5
This pack has no boron and uses whatever feldspar you’ve got, it’s for those that have limited access to materials - they can’t get frit or gerstley/gillespie borate or specific feldspar. Instead it uses zinc to melt the glazes.
Semi-matte: Frozen water
- Any Feldspar - just use what you’ve got.
- Zinc Oxide
How much should I buy?
Sue McLeod has a great intro to glazes. Check out her $100 list. Buy the materials you need, or buy them all and make more than one starter pack! Don’t forget you’ll also need 100g cobalt, 500g zironium and 500g rutile.
Mixing some tests
In order to test a variety of colours and effects, we are going to mix up a batch of each of the base glazes, divide it into equal pots and add a colourant to each pot except one, which will be clear. I suggest 5 different colourants to start, which requires 600g of each glaze. However, feel free to add more! To mix a glaze, weigh out the ingredients and add water until you have a creamy consistency. Mix well, put it through a sieve then divide into however many cups you have. This can be done by sight or more accurately, up to you. I recommend clear plastic cups. See this wiki entry for more on mixing glaze tests. John Post has a great video on mixing glazes. Note you can get a digital jewellery scale on amazon or ebay for less than 10 quid/dollars, which are great and you don’t need an electric mixer if you’ve got arms that work.
Below are some colourants. Each has a suggested amount. As each pot should have 100g of glaze in it, the percentage is super easy to work out. 1% = 1g of colourant. Sprinkle the colourant on top and mix really, really well. You can put it through a sieve but it will take a while as you’ve got so many. For now, just mix really, really well and get all the lumps out. You may need to add a drop more water to the version with tin, as tin makes things go really thick!
- 6% Tin oxide (Whites) - or use 10% zirconium, which is cheaper but not usually as nice.
- 3% Copper carbonate or 2% copper oxide (Greens, turquoises)
- 1% Cobalt carbonate or 0.6% Cobalt oxide (Blues)
- 4% Red iron oxide (Browns, Yellow ochres, rusty reds)
- 8% Rutile (Bone, beige. Does amazing things with other colours)
- Optional - 8% Stains (all the colours of the rainbow, but expensive),
- Optional - 1% Chrome (note that chrome is normally used for green, but goes a horrible brown if used in the same glaze as zinc. Combined in the right proportions with tin and calcium, it goes red!).
- Oxide is stronger than carbonate. If you take this into account you can swap between them pretty freely.
- Different glazes will react with colourants in different ways, for example turning copper green or turquoise. This can sort of be guessed at, but the only way to know for certain is to test.
So you now have some pots of glaze. What’s next? For each glaze, including the version with no colourants, glaze one test tile. Use a brush and put a coat over the whole tile. Once dry, put another coat on the top half of the tile. Now the fun begins. You now want to blend together a spoon of one glaze with a spoon of another, mix it up and glaze a test tile with that. Repeat for all combinations! You will end up with 21 different glazes for each base. Again, a pile of disposable clear cups is recommended for this.
- 6% Tin
- 3% Copper carbonate
- 1% Cobalt carbonate
- 4% Iron
- 8% Rutile
- Clear + tin (3% tin)
- Clear + copper (1.5%)
- Clear + cobalt (0.5%)
- Clear + iron (2%)
- Clear + rutile (4%)
- 3% Tin + 1.5% copper
- 3% Tin + 0.5% cobalt
- 3% Tin + 2% iron
- 3% Tin + 4% rutile
- 1.5% Copper + 0.5% Cobalt
- 1.5% Copper + 2% iron
- 1.5% Copper + 4% rutile
- 0.5% Cobalt + 2% iron
- 0.5% Cobalt + 4% rutile
- 2% Iron + 4% Rutile