NaMoPaiMo – How Underglaze Works


For someone used to painting with acrylics, the switch to ceramic underglazing requires a pretty significant change in approach. The techniques used are likely familiar, especially to someone who already uses an airbrush, but in almost every respect the materials behave differently.

I will be talking in a lot more detail about this once I start posting in-progress pictures, but I do want to set out some big picture ideas so those details make more sense.

Two kinds of “bodies”
To do what I do, I need a bare bisque ceramic. That is, a ceramic model that has been fired but has not had any form of glaze applied. For my purposes, there are two different kinds of bisques: earthenware and bone china. The Animal Artistry Hackney in the picture above was a bone china bisque. The Pour Horse Collier in front of him was cast in earthenware. I can glaze either type, but approaches that work with one don’t necessarily work with the other.

Two kinds of “paint”
Underglazes come it two types: opaque “cover coats” and translucent “easy strokes”. What makes the cover coats opaque is their clay content, and that makes them behave differently than the translucent colors. It also means they require a slightly higher firing temperature than the translucent colors. Which type gets used depends on what needs to be done. For instance, the thicker cover coats work well with scraffito (where they give a crisp edge for a white pattern) but not nearly as well as erasing (where they tend to “pile” instead of giving a soft edge to a dapple). And to make things even more interesting, the individual colors within these two types vary in their properties. There are, for instance, cover coat colors that cannot be etched (Darkest Brown) and translucent colors that are remarkably opaque (Black) when applied.

Two kiln settings
Most underglazing uses two different kiln settings – bisque (Cone 04) and glaze (Cone 06). The bisque firing is the higher temperature. Think of the zero in cone numbers as “negative”, so -6 is lower than -4. Opaque colors require that hotter fire to mature, but once there is glaze anywhere on the model it can only fire at the cooler setting. (Ceramic artists who work with overglazes are firing at much cooler temperatures.)

You are not just mixing pigments
Unlike traditional cold painting, color in fired ceramics is not just about pigment. Instead, colors are achieved by chemical reactions. For instance, iron is used to get red tones, but it requires oxygen to develop. For that reason, many smaller kilns with fewer peep holes give more muted red tones than larger kilns. It is also why the first thing an underglaze artist will tell someone is to avoid any color with the word “cobalt” in the name, because it will tint everything green. Not just that area or that model, but the entire load in the kiln. The “chemistry” aspect is part of what makes underglazing more than a little unpredictable, which can be unnerving when you consider that bisque bodies are difficult for most artists to obtain.

What you see is not what you get
Because the final color is based in chemistry, the material you are painting might not look anything like it should. Companies that manufacture underglazes tint them to approximate their final color, but it is really just an approximation and some colors are closer than others. If you do a lot of underglazing, your eyes develop the ability to “translate”, but it takes a while. Also, those colors with a clay content then to be chalky and give the appearance of being opaque long before they actually are. This means that beyond the first couple of coats, you are adding your shading blind, using only your memory of which areas you hit with more color.

What you get may not stay there
Some colors are less stable when fired than others. This is particularly true of reds or colors with a red content, like the “pinking” on a nose. For that reason these colors usually get added during the last fire.

No touching!
And finally we get to the really difficult part: you cannot touch where you have painted. Raw underglaze is little more than a surface of powder. If you touch it, part of it will come off. Even worse, remember that thing about how the cover coat colors look opaque before they are opaque? That means that if you mar the finish you may not see it until later, after the horse has been glazed. Underglaze that has been fired is only slightly more durable. A huge part of underglazing is planning how you intend to hold the horse, and how you plan to protect what you have already painted.

So to summarize, you will be navigating which type of colors to use, and when those will be fired and at what temperature, all while figuring out how to hold a fragile model without touching any of your work. But it isn’t all hard. I’ll end with one thing that is so much easier about ceramic work, and a strange quirk you can use to your advantage.

Never worry about white again
If you paint appaloosas or pintos, or even just a horse with flashy white markings, you know how much effort goes into creating a smooth, opaque white. With ceramic underglazing, white is the default. If you don’t do anything, you get opaque white. In the case of earthenware, it is even a very realistic warm white. White areas are also your best chance for a good no-muss handhold. If you are going to try your first underglaze project, something with broad areas of white that cover safe handholds—tobianos and large snowcap blankets, for example—is probably your best bet.

Here I have begun to add the paler colors that will sink under the darker shading. The chalky tan will disappear under the black mane, but will be visible as a golden tan at the lightest part of the poll.

That quirky thing
Underglaze painting is done light-to-dark. This is not optional. At most, a really opaque color may “muddy” a darker one, but even that is hit and miss. For the most part, lighter colors just sink down under darker ones. And that “sinking” is something underglaze artists have learned to use to their advantage.

See those horses at the top of this post? They are both dapple bays – or will be. In both cases, the dark shading and dappling has been done first. The Hackney is dark dappled bay, and the Collier is a mealy bay with transitional dapples on the barrel. The Collier is early in the process, with just the hint of the dappling pattern set in pale gold. The next few steps for him will be deeper red-brown tones where the dapples fade into the darker top line. The Hackney has all of his dappling set and is ready for the final step, which is adding the red-gold and gold under the dappling. That will be added over the top, and he’s going to look sickly yellow-green for a while, but those colors are going to sink down under all the dark details you see now. When it is done, he should look like a deeper, redder version of the color you see on the horse in the masthead of this blog.

I’ll pick up tomorrow with photos of that, since that is today’s work. I’ll also give a more detailed explanation of what has been done with him up until now, and what the next steps are. I also have a different horse that we’ll follow start-to-finish, beginning with pattern design.

One Response to NaMoPaiMo – How Underglaze Works

  1. Sarah Townsend February 10, 2017 at 9:16 pm #

    We worked a bit with underglazes in my college ceramics course (handbuilding), but it was mostly to color slips and create bases. So this is fascinating. I didn’t realize there was that much difference in how they would work on earthenware and bone china. Sometime I’d like to actually play with glazing a horse (or horse tile).

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