Glazing is an incredibly important step in the ceramic making process, adding colour, texture, and shine to your work. Choosing a colour for your ceramic piece seems like a simple enough task, however the glazing process is certainly anything but simple. I still personally can't decide whether it's science or magic perhaps i’ll let you decide after reading this post.
Many factors come into play to create the many colours and effects of a glaze, not only the composition of the glaze itself, but also factors such as clay body it is used on, the application of glaze, firing times used and temperature of the firing. Even location in the kiln itself can all have influence on the end result.
The full process and understanding of glazing is extensive, even before you consider stepping into the world of making your own glazes. This article aims to cover a small section on glazing and will focus on the use of, and the layering of, commercially prepared brush on glazes to create new exciting effects and colours. Layering glazes is something I have spent considerable time developing over the past couple of years as I work through my ceramic journey, and allows me to share some of my experiences.
However, before we jump into drooling over some delicious colour combinations, lets just touch on some glaze basics for those unfamiliar with the general process of taking a ceramic piece through glazing.
Glazing Basics
Composition
Glazes are composed of various materials, including silica, alumina, and fluxes, which melt and form a glassy coating on the ceramic body when fired. The composition of a glaze determines its colour, opacity, and texture.
The final colour of the glaze once fired is vastly different that what is shown when you apply. An example of this is some of the blue glazes I use regularly are bright red in the bottle and only when firing does the blue appear.
Many experienced ceramic artists will develop their own formulation of glazes meticulously testing different ratios of individual components creating their own unique colouring and style. However, there are many commercially available glazes that are a popular option for many (including yours truly).
On the glaze bottle it will indicate what type of clay it should be used on (such as stoneware or earthenware), what temperature it needs to be fired to and how to apply. Glazes can be applied either by dipping, spraying, pouring or brushing.
The information listed in this article will be covering use of commercially available brush on glazes using stoneware clay bodies.
Firing processes
A glaze firing is actually the second firing a clay piece will go through in it's journey to magnificence.
The first firing is called a ‘bisque firing’. This happens after you have made your piece and it has dried fully. Fired at a lower temperature than a glaze firing, it hardens the clay while still allowing it to be porous enough to absorb the glaze you will apply.
Once it has been bisque fired you can then apply your glaze, once the glaze has dried it can be loaded in the kiln.
The glaze firing process involves bringing the kiln slowly to the desired temperature, and then cooled slowly back to room temperature before unloading.
The full glaze firing usually takes a couple of days to complete before it's safe to unload. Typically you use that time to pray to the kiln gods, and overthink all the things that could go wrong - perhaps that's just me...
The program of a glaze firing will depend on the firing requirements of the glaze and clay body.
For example:
You may have a glaze that can be fired between 1200°C-1240°C and a clay that requires a firing temperature of 1220°C - 1300°C.
The firing temp you would be aiming for a firing 1220°C - 1240°C to allow both to sit within optimal ranges.
Underfiring your clay means that the end product may not be water tight and over firing your glazes could drastically mean you lose the beautiful colourings.
Glaze Testing
Ok, so now we have some basics covered let's jump into the good stuff of glazing and how we start working towards the beautiful combinations we know and love.
Before we layer glazes together, we need to ensure that the glazes we have chosen work with the clay and the preferred firing conditions, and that we know what colours we would expect.
I choose to do my glaze testing using bowls. They can be easily organised by stacking and I also get a chance to practice my bowl shapes. It's a win/win.
I use skinny paper tape to split the bowl into segments before applying glaze to each section. I then use an underglaze pencil to mark on the outside of the bowl which glazes were used in each section. Underglaze pencil is designed to withstand the firing and will stay on the bowl after firing. On the base of the bowl I indicate the number of layers of glaze used and the firing temperature.
The images here show what some of the glazes look like on stoneware, used on their own (not layered) once processed through a glaze firing.
Glaze Layering
While most commercial glazes are designed to be used on their own, layering different glazes can create unique and unexpected beautiful effects.
I spent over a year playing with layering glazes to see what effects I could produce. The glazes I used were primarily Botz Glazes and Amaco Glazes. Generally I found the best results were gained when you stick to using the same brands of glazes together, rather than mixing brands.
To set up a test for layering glaze, as above segments are made using tape and bowls labelled. However this time we would apply the first glaze and then put a second glaze on top before firing. You can get drastically different results by either putting the glaze on top or the bottom of the other and thus if I did one way round in the inside, i'd do the opposite on the outside for comparison.
Each bowl will have the same core glaze used on all segments and then 8-10 glazes chosen to layer it with. Each segment will only have max 2 glazes to show desired effect.
Example:
'Blue midnight' is my core glaze
I have 8 other glazes to layer it with
On the inside of the bowl I choose to use Blue midnight on top of the other glazes
On the outside of the bowl I would do the opposite and have Blue midnight underneath.
Each segment will have written in underglaze pencil what two glazes are present
You can imagine the many hundreds of combinations of glazes you could discover when you have a large selection of glazes to play with.
You also have the choice of how many layers of each glaze to use - you could use the same number of layers or one could have more than another. Each will give varying effects.
Testing requires much patience but by experimenting it allows you to discover new results and find some amazing combinations (and certainly some many less desirable ones).
Layering on Ceramic Items
Just incase you aren't exhausted enough by the testing phases, once you have your test bowls you then have to decide how you may actually apply them on your work, and if you want to look at using more than 2 glazes and how you may layer them.
I often make small pots like the one below to try more complicated layering once I have a basic understanding of how the glazes will perform together.
This little bud vase below has 6 different glazes used. The glazes all have varying number of layers and and overlaps to create a gradient effect.
Getting started with glaze testing can be a bit overwhelming but there are some very helpful resources out there on how to get started. There are even some groups dedicated to layering glazes such as AMACO Cone 5-6 Glaze Forum on Facebook, a community of over 100k members who share results daily of their results of layering Amaco glazes, and helped me start choosing which glazes to start my layering journey with.
Something I am also developing continually is a dedicated a section on my website to some of my results of glaze firings and some of the firing conditions that have worked. Not only do I hope this may help others in creating their own versions developing their own combinations but allows as inspiration for others looking to have commission work.
You can check out my current list of glaze combinations here: Glazes Combinations
Conclusion
Layering glazes and glazing in general can be a very rewarding and creative aspect of ceramics. You can create unique and beautiful pieces that reflect your personal style.
My key bit of advice to customers and other venturing into glazing and testing combinations is to be mindful when managing expectations of results. Although similar results can be achieved with the same glaze combinations, every application and firing will provide different results and variations should be expected.
One thing you can most certainly guarantee is that each handmade glazed ceramic item made will be one of a kind, and despite the unknown there's nothing quite like the feeling of opening that kiln and seeing a world of colourful wonders that welcome you
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