Exploring One Glossy Glaze with Many Colours
Create a palette of compatible glazes
When you first start mixing your own glazes, it can be overwhelming to decide on which glaze recipes you’re going to use. There are so many! There are literally thousands. On Glazy.org right now, there are over 20,000 published recipes. Some are clay bodies and slips and other ceramic recipes, but most of them are glazes.
How do you pick one or a couple to start with?
I highly recommend keeping things simple at first. A good recipe to start with is a glossy glaze. Glossy glazes are great for using on the insides of mugs and bowls because they are less likely to stain and cutlery mark, and they are nice and smooth for washing.
So if you’re going to choose one recipe to start with, I’d pick a glossy glaze. Then you can branch out from there.
Now you might be thinking “One glossy glaze? That’s so boring! I’m not going to glaze all of my pots with one glossy glaze. Where’s the fun in that?”
But here’s where the fun starts.
With one glossy glaze, you can create a whole rainbow of coloured glossy glazes. You just need to add different colourants.
Here’s an example of a glossy glaze recipe. This base glaze is called “GME BGP” and it is the glaze I use as an example while teaching how to mix glazes and do colour runs in my “Glaze Mixing Essentials” (GME) course. BGP stands for “Blue Green Pink”, which is the base glaze from one of the many studio glazes at the studio where I used to work as a technician. The studio recipe was made with copper oxide and tin and it was blue-green in oxidation and pink/red in reduction.
No colourants are added, so this glaze is just clear. We often call a glaze recipe with no colourants added, a base recipe. The photo on the right shows the BGP base glaze on 4 different clay bodies – L-R Plainsman P300, M370, M340, M390.
A glossy base recipe with no colourants added is often clear, but sometimes it will be cloudy or white. The quality, transparency/opacity of the base glaze is going to affect how it looks with colourants added.
The chemistry of the base glaze, and which materials it is made of will also impact how it looks with colourants added. Just keep this in mind, so you’re not expecting every glossy glaze to look the same when colourants are added. That’s also why it’s fun to do colour runs with different recipes, because they can all turn out quite different, even with the same colourants.
Testing a base glaze with different colourants is called doing a “Colour Run”. I highly recommend testing small batches before making a big bucket of any glaze you haven’t used before.
We can do a colour run by adding different colourants/opacifiers and different percentages of colourants/opacifiers to our base recipe.
The 6 most common colourants are:
- Copper
- Cobalt
- Iron
- Manganese
- Nickel
- Chrome
Opacifiers change a glaze from transparent to opaque by blocking the light from passing through. The 4 most common opacifiers are:
- Rutile
- Titanium dioxide
- Zirconium silicate (Zircopax, Superpax, Ultrox)
- Tin oxide
Colourant Results
In this colour run, I chose to test 4 of the 6 colourants. Copper, Cobalt, Manganese and Iron are the most common of the 6 colourants listed above. Chrome and Nickel are a bit less common and there are more colourants not listed that are even less common. You can create a lot of recipes with the 4 that I tested.
Here’s what happens when I add 1% Copper carbonate to this base recipe.
And then when I increase from 1% to 3% copper carbonate, you get a deeper colour. You can especially notice the difference on the buff stoneware (2nd from right) where 1% copper wasn’t really enough to make the colour of the glaze over-power the colour of the underlying clay body but 3% copper makes the colour really vibrant. Testing your glazes on different clay bodies is important, because the difference can sometimes be surprising.
Now let’s look at Cobalt carbonate as a colourant. Here is the same base glaze with 0.1% cobalt. Cobalt is a stronger colourant than copper, which is why I used such a small amount to start.
Now here’s the glaze with 1% Cobalt carbonate. See how just 1% cobalt gives such a strong blue colour?
Next I tried 1% Manganese dioxide. Manganese is nowhere near as powerful as cobalt, so 1% gives a very light hint of colour.
But with 3% Manganese dioxide, now we are getting more of a brown colour.
And the last colourant I tested is Red Iron Oxide. Iron is also not a super strong colourant. I knew from previous testing that 1% doesn’t give the glaze much colour so I tried 2%.
And then I tried 10% Red Iron Oxide! This might seem like a lot, and it would be for any other colourant. But iron is the one colourant that is commonly (and safely) used in high percentages. Notice how the glaze went from a light tan colour to a dark brown. It would be interesting to test some of the percentages in between 2% and 10% to see the transition and change of colour.
You can see that this glaze is starting to run a little bit (notice the drips on the lower sides of the test tiles) and this is because iron is also a flux. Fluxes lower the melting temperature of a glaze. Copper, cobalt and manganese are also fluxes, but since I used them in such small quantities, they didn’t affect the melting of the glaze very much. 10% of a colourant is a significant proportion of the recipe, so keep that in mind if you’re using high percentages of iron, that your glazes could run.
Opacifier Results
In this colour run, I chose to test 2 of the 4 opacifiers listed above – Rutile and Zircopax.
Here, you can see the glaze with 10% Zircopax. Zircopax is zirconium silicate and is often used at 5-10% to opacify a glaze. It essentially turns a clear glossy glaze into a white glossy glaze.
Notice how the glaze on the right test tile is white, but the clay body is dark. In all the colourant examples above, you could see the colour of the clay body through the transparent glaze. Seeing an opacified glaze on a dark clay body is a good way to understand how opacifiers work.
You can also combine opacifiers with colourants so I could take a transparent blue glaze with cobalt and add zircopax to make it an opaque blue glaze. This can help to make colours stand out on darker clay bodies.
And my final example is with 5% Rutile. Rutile is also an opacifier, but it is not stark white like Zircopax. Rutile is composed of titanium and iron. The yellow colour you see is from the iron. But unlike pure iron, you can see how the glaze is less transparent on the dark clay body.
Unlike the whiteness of Zircopax, you get little flecks throughout the glaze. These flecks make the glaze more variegated and less of a uniform colour. Rutile is often used in combination with other colourants, and can create different shades and tones of colours from what you would get with the colourant alone.
If you are interested in any of these glazes, here is the Glazy.org bookmark that includes all of these colourant test recipes (remember: they are all the same base recipe, but with different colourants).
Colourant testing is a gateway to the addictive glaze testing rabbit hole
Learning how to do a colour run was what got me completely hooked on glaze testing. When I was in art school back in 2009 doing my clay diploma program, one of our assignments was to take 2 base glazes and test them each with 45 different colourant variations! It was a LOT of work, but I loved it so much and from that point on, I became obsessed with glaze testing.
I rarely use a new glaze without testing it with different colourants now. I often start with copper, cobalt and iron and then expand from there if I’m interested enough. If you like how the glaze looks and feels, then why not have a few different colour options?
Here are some other colour run examples. Each photo has the same base glaze with different colourants. Sometimes I test 3 and sometimes I test 18. It just depends on what I’m looking for.
L-R: Red iron oxide, Nickel oxide, Copper carbonate
L-R: Varied percentages of Nickel oxide, Red iron oxide, Copper carbonate, Cobalt carbonate, Iron chromate, Manganese dioxide
L-R: Base, Copper carbonate, Nickel oxide, Iron chromate, Red iron oxide (fired in oxidation)
L-R: Base, Copper carbonate, Nickel oxide, Iron chromate, Red iron oxide (fired in reduction)
L-R: Base, Nickel oxide, Copper carbonate, Red iron oxide
Once you see how exciting colour runs are, there’s a whole world of glaze testing that you can continue to explore.
Learn how to do your own colourant testing
If you want to learn how to mix glazes from scratch and do your own colourant testing exactly like you see here, this is what I teach in my online course Glaze Mixing Essentials. In this course, I will teach you everything you need to know to mix any glaze recipe and then test it with different colourants so you can have your own unique coloured glazes.
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