# data[].attributes.body
Hard slab.

# data[].attributes.body
A bit late, but better than never. Still need to paint it when it dries more.

# data[].attributes.headline
Linda Vu - 80 - Coil Pot - This is supposed to be a "pansy blue" color after firing. 

# data[].attributes.subject
Linda Vu - 80 - Coil Pot - This is supposed to be a "pansy blue" color after firing. 

# data[].attributes.attachment_caption
I made a set of 8 (or two sets of 4?) porcelain coasters. I used stamps to create a fun floral design!

# data[].attributes.body
Katherine Francisco

Art 84

Set of coasters

# data[].attributes.attachment_caption
I'm making a set of large plates and a matching set of small plates. The design is simple, glazing in blues & whites will be a highlight, plus swirls on bottom!

# data[].attributes.body
Katherine Francisco

Art 84

Sets of large and small plates

# data[].attributes.attachment_caption
This is a set of hand-built nesting platters. they are fairly small and oblong. I see using them for cheese and crackers or other appetizers.

# data[].attributes.body
Katherine Francisco

Art 84

Nesting platters

# data[].attributes.attachment_caption
Here is a set of nesting pinch pot bowls that I made. I added a small heart stamped in the inside middle of each of the nesting bowls as a detail.

# data[].attributes.body
Katherine Francisco

Art 84

Nesting pinch pot bowls

# data[].attributes.headline
Art 82 - Historical Coil - Mackenzie Robertson

# data[].attributes.subject
Art 82 - Historical Coil - Mackenzie Robertson

# data[].attributes.attachment_caption
Here is a small bowl that I threw on the wheel, trimmed the bottom of, and then carved.

# data[].attributes.body
Katherine Francisco

Art 84

Small bowl w/ carvings

# data[].attributes.attachment_caption
Here is a bowl that I threw. I decided to keep this one simple with no carving so that glaze can be it's standout feature. I am proud of the trimmed bottom.

# data[].attributes.body
Katherine Francisco

Art 84

Small bowl (simple, no carving)

# data[].attributes.attachment_caption
I threw this on the wheel. I am still deciding if it is a cup/mug or a planter pot. I am working on carving and also trimming the bottom of wheel-thrown pieces.

# data[].attributes.body
Katherine Francisco

Art 84
Large mug/cup or small planter pot

# data[].attributes.attachment_caption
I created this yunomi/teacup using the kurinuki method. I am especially proud of the even wall thickness and the inside design which is why I chose this picture

# data[].attributes.body
Katherine Francisco

Art 84

Kurinuki teacup/yunomi

# data[].attributes.attachment_caption
I created these serving slabs as a mismatched pair. They are both asymmetrically shaped. I envision using them for cheese, charcuterie, or salmon.

# data[].attributes.body
Katherine Francisco

Art 84

Serving platters/slabs

# data[].attributes.headline
Art 82 - Historical Coil vase wet work - Mackenzie Robertson

# data[].attributes.subject
Art 82 - Historical Coil vase wet work - Mackenzie Robertson

# data[].attributes.body
was inspired by the skyphos form

# data[].attributes.attachment_link.readable_text
The Pottery Wheel is supported by its readers. If you click one of my links, I may earn a commission. I'm also a participant of the Amazon Affiliate Program and will make a commission from qualifying purchases. This helps me keep the website running. Thank you, I really appreciate your support!

Underglaze and glaze do have some shared properties and functions. However, there are significant differences. After a bit of investigation, I discovered the following:
Underglaze and glaze can both be used to decorate a piece of pottery. The difference is that underglaze is applied before a clear glaze. It is easier to use underglaze for intricate designs. However, a clear overglaze will seal the piece and make it non-porous.
There are a number of differences between underglaze and glaze. I'm going to take a closer look at these differences in the following article. I will also explore, what, why, how, and when there is a difference between an underglaze and a glaze.

First, I will give you a broad overview of the different kinds of underglazes and glazes. Then I will look at the specific differences more closely.

The Broad Differences Between Underglaze and Glaze

Underglazes can be split into three categories:

Colored slips that can be applied to wet clay. These are a mixture of clay, water, and pigment.

Engobes that can be applied to bisque ware . They contain silica and glass.

Traditional underglazes that are applied to greenware at any stage before it is fired. These contain colored metal oxides.

Glazes contain glass-forming ingredients that create a non-porous glass layer when fired.

They are also normally applied to bisque ware but are occasionally applied to greenware if they are single fire glazes.

The Different Ingredients in Underglaze and Glaze

In this section, I will look at the differences and similarities in the ingredients of underglaze and glazes.

Clay in underglaze and glaze

An underglaze that is going to be applied to leather hard clay before a bisque fire needs to contain a significant amount of clay. The reason for this is that the pottery dries out and shrinks before it is fired. Consequently, the underglaze needs to shrink at the same rate.

If the ware shrinks more than the underglaze it will flake off. Similarly, the ware will shrink when it is fired. Therefore, the underglaze needs to shrink at the same rate to avoid flaking.

Unlike underglaze, overglaze does not contain clay particles as such. Glaze has ingredients, including the minerals alumina and silica that are derived from clay. However, they are not of themselves clay particles.

Alumina is used to stiffen glaze so that when it is in its melted state, it does not simply slide off the pottery being fired. Silica is a glass-forming component in the glaze.

Underglazes must contain a small amount of gum. The gum does a couple of things. Firstly, it slows down the rate at which the underglaze dries. This makes it easier to apply the glaze with a brush. Hence why it is called a 'brushing gum'.

Because the underglaze does not dry immediately on contact with the ware, it is more spreadable. (A handy comparison, is thinking about how difficult it is to paint a newly plastered wall that has not been sealed).

Secondly, the gum makes the underglaze sticky, which means that it adheres to the surface without slumping.

Also, the gum content in underglaze is one of the reasons it can be applied to bisque ware. Underglaze contains clay, and this suggests that it might shrink and flake off when applied to bisque. However, the gum content of the underglaze enables it to stick well to the bisque, without cracking.

Glaze does not, as a matter of course, contain 'brushing gum'. A potter can, however, add it if they want to have greater control over how they apply the glaze to a piece. Adding gum to a glaze will thicken it a little and make its consistency more like that of an underglaze.

Here is an interesting video by The Ceramic Arts Network, experimenting with gum in glaze.

Glass in Underglazes

Some underglazes contain more glass-forming properties than others.

Originally underglazes were simply colored clay slips. A colored clay slip is a mixture of clay, water, and pigment. Because slip is made of clay, it does contain silica, which is a glass-forming substance.

However, more recently, underglazes have been created that contain frit. Frit is a ceramic compound that contains silica. If an underglaze contains more frit than clay, it will melt in the same way that glazes melt when fired.

What kind of underglaze a potter decides to use depends on how they intend to apply it. For example, if an underglaze is going to be applied by dipping it needs to contain less glass. This is because dipping covers the piece completely. If an overglaze is going to adhere to the ware, the water in the glaze needs to be able to pass through the underglaze and absorb into the clay body.

When underglaze is very glassy, the water from the overglaze will not be able to pass through and the glaze will not adhere. Instead, the glaze will ball up and roll off, a bit like rain on a polished car.

Glass producing ingredients in an underglaze helps it to stick to the clay body. However, if they contain too much glass, this will cause the colors in the underglaze to bleed when they are heated. One of the valuable qualities of underglaze is that it can be used for intricate design. It is important that this is not compromised by adding too much glass to the mix.

Glass in Glazes

Glazes are essentially a glass layer on the pottery ware. A glaze consists of ground-up materials suspended in water, which is applied to the piece. When it is fired, the ingredients melt together to from glass.

The clay body and the underglaze contain glass-forming ingredients. However, when the glaze is fired, all the particles in the glaze melt to form glass. None of the ingredients in the glaze keep their original crystal composition.

Because underglaze is used for decoration it invariably contains color. Over glazes can be colored or clear. The coloring ingredients in underglaze and a glaze are usually metal oxides.

Both underglaze and glaze can be used to add color and design to a piece of pottery.

The differences between a colored underglaze and a colored glaze are as follows:

Because underglaze has a much lower glass content than glaze, it can be used for much more detailed decoration. Fine details can be painted onto greenware or bisque ware and it will not run or bleed as much as a colored glaze.

Underglaze can lose its pigment if it is fired in the kiln at too high a temperature. Some colors are more resilient at higher temperatures than others. For example, cobalt blue can survive higher temperatures than other colors, which can turn black if they are overheated.

Interestingly, this is one of the reasons why a lot of design on porcelain has historically been blue. Porcelain is fired at higher temperatures and blue was one of the colors that could survive the process.

By contrast, glazes can retain very vivid colors when fired at higher temperatures. In particular, glazes that are fired in the mid-temperature range, through a process of oxidation, create very bright colors.

The Different Reasons Why We Use Underglaze and Glaze

It is too simple to say that underglaze is used for decoration because of course, overglaze can be extremely beautiful too.

However, here are some features that distinguish underglaze from overglaze:

Why We Use Underglaze

As stated above, underglaze can be easier to apply with a brush than overglaze and is better at times for intricate and detailed design. Furthermore, the look of the final product is more controllable with underglaze. This is because it does not bleed or feather as much as glaze when it is fired.

Also, the color of wet, unfired underglaze is similar to its color once it has been glazed. This is another reason why underglaze is popular for decoration. Potters have a better idea of how the fired piece will look.

By contrast, overglaze often looks very different before it has been fired than afterward. It can be hard to predict what a glaze will look like. Therefore, it is often recommended that you practice with glazes to get the kind of effect you are going for.

In addition to this, sometimes after the bisque fire, the underglaze has imperfections that need to be touched up. Applying underglaze to greenware gives the potter a chance to finesse their design before the glaze fire.

Also, a second coat of underglaze can be applied after the bisque fire. This can be useful if the colors have burnt off a bit in the first fire.

Finally, using an underglaze for decoration with a clear overglaze can be cheaper. One way of getting an intricate design using overglaze is to use a technique called overglaze decoration.

In overglaze decoration, colored decoration is painted onto a glazed surface. The pottery is then fired a second time to fix the painted decoration. However, because this method involves two glaze firings, it is more costly and time-consuming.

Why We Use Glaze

On the other hand, glaze has important properties that underglaze does not have. These are:

Because glaze seals the surface of the pottery completely, it creates a barrier. This barrier can help with something called 'food safety'.

The term 'food safety' is used in a couple of different ways. In one usage the glaze is seen as being a barrier that protects the pottery. For example, preventing the pottery from being stained by food and drink.

However, 'food safe' also refers to whether the glaze itself is safe to eat and drink off.

It is important that glazes are responsibly produced and reliably tested. There has been more awareness recently around toxins leaching from ceramics into food ¹.

That being said, assuming that a glaze has been responsibly produced, it does provide a glass-like barrier. This barrier enables the piece to be used for more purposes than an underglaze alone would afford.

The Difference Between How We use Underglaze and Glaze

Both underglazes and clays can be applied to a piece using broadly similar techniques. For example, both can be painted to a piece of ware.

However, glaze and underglaze have different properties. Therefore, whilst you may be able to paint both, the experience and the effect will be different.

For instance, glaze that you can paint has quite a thick consistency. A little like heavy cream. As such they are not ideal for finer details.

By contrast, underglaze can be painted on in quite a watery state. This means that different layers of color can be built up. Also, underglaze can be painted on much like a watercolor. Used in this way, different colors can blend into one another creating a gradient look.

Because glaze that you can paint is thick, you have to be careful how many layers you apply. Applying too many layers of glaze can cause it to slump, drip and deform in the kiln. Whereas, you can apply up to six layers of underglaze without that worry.

Although single fire glazes can be used, normally it is applied to bisque ware.

Some of the ways that glazes are commonly applied:

Dipping the ware in the glaze

Painting with the glaze

Pouring the glaze on or around the ware

Spraying the glaze with an airbrush

Sponging on the glaze

Underglaze can also be applied using the above methods. In addition to this, there are other techniques that can add details to the pottery.

For example, underglaze can be drawn onto bisque ware. Underglaze pencils, crayons, and pens exist for this purpose and can be used to create very fine details on a design.

Alternatively, a potter may want to use a bulb syringe to apply underglaze to a piece. This technique is a little like slip trailing . Slip trailing with slip can create quite a defined texture on the piece. By contrast, using underglaze, in the same way, does not create textural patterns. However, a bulb syringe can be used to create lovely color designs.

Another advantage of using underglaze is that you can mix underglaze colors together. This can be done either as you paint your piece. For example, mixing watercolor style paints as they go onto the bisque.

Or you can mix the underglaze up prior to application, to create a color that is to your exact preference. This differs from regular glazes which generally cannot be combined together to create a third color.

The Difference Between When We Use Underglaze and Glaze

Although single fire glazing is an option, most of the time, glaze is applied to bisque ware. Part of the reason for this is that bisque ware is porous and absorbs the water from the glaze. The result is that the glaze adheres to the piece.

By contrast, many modern underglazes are designed to be applied either to greenware or to bisque ware. In fact, underglazes can be used on wet clay, leather hard clay, bone dry clay or bisque ware.

When you apply the underglaze depends on the kind of underglaze you are using. For example, if the underglaze is a colored slip, it can be applied to wet clay. Whereas an underglaze pencil needs to be applied to bisque ware. If a pencil was used on unfired clay it could damage the surface of the piece.

Another factor that impacts when an underglaze is used is the water content involved. For example, underglaze can be applied to greenware. However, the water in the underglaze can soften the clay in the ware and compromise its shape or design. As such, it can be easier to apply a wet underglaze to bisque ware.

Having said that, if you dip underglaze in clear overglaze, the colors in the underglaze can run. So, there is also an argument for applying the underglaze to greenware, firing it, and then glazing it.

Final Thoughts

In this article, I have looked at the what, why, how, and when underglazes are different from glazes. In short, glazes produce a glass-like layer, usually over the whole of the ceramic work, except for the base. This layer is protective, but it can also be decorative.

Underglazes are more versatile in their decorative capacity. However, although they can be vitreous, they don't offer the same protective layer of a glaze. So, whilst an underglaze can enable detailed decoration, a glaze offers a glass-like layer of protection.

If you enjoyed this post, please share it!

References:

1) https://ehs.princeton.edu/health-safety-the-campus-community/art-theater-safety/art-safety/ceramics

# data[].attributes.attachment_link.title
The Difference Between Underglaze and Glaze - The Pottery Wheel

# data[].attributes.attachment_link.description
The Pottery Wheel is supported by its readers. If you click one of my links, I may earn a commission. I'm also a participant of the Amazon Affiliate Program and will make a commission from qualifying purchases. This helps me keep the website running. Thank you, I really appreciate your support!

# data[].attributes.body
Underglaze will turn blue.

# data[].attributes.body
I was inspired to make something for Halloween: a casket (even if we aren't getting it back in time for this year). My slabs were pretty thick, and it wasn't drying. So, sanding off the mishima wasn't working well, and it ruined the nice canvas texture from rolling the slabs.

# data[].attributes.body
I forgot to post my Nicho box in Padlet, here it is! Currently finishing up my coil pot.

# data[].attributes.body
This was my third try at the mug, it took a bit to get better at rolling out an even slab, I found the French rolling pins easier. I made the mistake of using a hair dryer to dry my slab (probably should've used it without heat), and it was cracking as I was folding it. Third try was best.

# data[].attributes.attachment_link.readable_text
Great Advice for Preventing Ceramic Warping

Minimizing the Effects of Ceramic Warping!

All potters learn early on in their careers that clay has a memory. Clay memory, or clay particle orientation that is affixed by physical/ionic properties, is what can cause ceramic warping. This is because the clay particles tend to return to their initial orientation when they begin to dry out.
In today's post, an excerpt from the Ceramics Monthly archive, Thomas Anderson explains how to predict and manage ceramic warping prior to firing your work. - Jennifer Poellot Harnetty, editor.

PS. For more technical detail on the factors contributing to clay memory and ceramic warping, check out the September 2019 issue of Ceramics Monthly!

Knowing what causes memory is one thing, knowing how to minimize its effect is another. The first issue to understand is that high-plasticity clays often have high memory. Porcelain is more prone to memory issues, but any highly plastic clay body is susceptible. The second issue is water. The more water you add to a body during forming, the more you increase the likelihood of memory issues. The heavy slip that comes up when you throw indicates you are washing out fine particle plasticizers on the inner and outer wall, which in turn softens them and changes the ionic charge they carry. You have created differentials in surface tension, ionic charges, and particle alignment between the inner cavity and outer walls.

Learn all about buying and using pottery clay when you download this freebie, Successful Tips for Buying and Using Pottery Clay.

Another memory factor to consider is uniformity of the formed piece. Does this piece have uniform wall thickness, and/or do the attachments such as handles or other ornate additions have the same thickness? While ornate features make a piece attractive, they can also create drying issues including warping. Obviously thin walls will dry faster than thick walls, which is multiplied if they are very thick or very thin. Thick or weighty attachments made to thin walls can amplify the effects of memory. Damp boxes and plastic are used to help facilitate an even clay drying process. Wrapping work in plastic requires monitoring and judgments to be made as to when to remove the plastic. Light misting can also slow down drying of thin-walled areas, but care is required not to over saturate the clay with water. Sponging should be avoided as it will unevenly moisten a piece as well as remove fine particles and erase detailing.

Slab and tile work are the most susceptible to warping caused by memory. Prevention begins when rolling slabs. Roll in multiple directions-not just one. Smaller pieces can be flipped half way through the process. Large slabs formed on a slab roller should be rolled in both directions, forward then backward. Rolling in one direction stretches the slab as much as it compresses the slab. Unequal compression can add to memory issues, and cause the slab to be more susceptible to quartz inversion stress when firing. Cut pieces from the center of the slab and avoid the outer 2 inches around the perimeter if possible.

The preferred method for handling ceramic tiles after being rolled is storage on drywall ware boards. While this method works, I prefer to use 1/2-inch Sande plywood, which absorbs and releases moisture at a slower rate and does not flex when lifted. I roll and cut tile on the plywood to avoid any additional handling of the clay. Placing a second piece of plywood over the tile adds just enough weight to lightly compress the tiles and helps prevent warping. Tiles and slabs will shrink while drying, so use enough weight to hold them flat, but not so much you create drag as they dry. Memory is a clay property that you have to manage as part of your forming process.

To control warping caused by memory issues, you primarily have to control the rate of drying. In addition, moisture content must remain uniform across the entire piece, whether it be a large bowl or a flat tile. Small, thin-walled bowls and cups are popular, but thin-walled pieces are susceptible to memory issues. Thin walls are less resistant to the stress and pull. For example: thin tiles warp more than thick tiles due to the dispersion of stress. Thin attachments to thicker pieces are also susceptible to memory issues. The shrinkage rate supplied by your clay supplier should also be considered. Highly plastic bodies have higher levels of plasticizers, which mean higher water content. Shrinkage rates above 12.5-13% indicate high plasticity, making those bodies more susceptible to warping due to memory. For slab or tile work, keep the shrinkage rates to 12% or under.
the author Thomas Anderson has spent the last decade researching technical papers from various universities on clay formulation. He is currently writing formula limits for clay chemistry.
**First published in 2019.

Learn all about buying and using pottery clay when you download this freebie, Successful Tips for Buying and Using Pottery Clay.

Related Posts

Tags
Add:, additions, attachments, avoid, body, bowl, bowls, boxes, careers, ceramic, changes, charge, clay, clay body, compress, compression, consider, content, control, create, created, creating, cups, cut, damp, detail, diameter, direction, dispersion, dry, drying, drywall, effect, effects, erase, even, excerpt, features, firing, formed, forming, forward, handles, handling, help, hold, inversion, inversion stress, ionic charge, issue, issues, large, learn, levels, make, making, mean, memory, moisture, negative, neutral, original, ornate, particles, perimeter, piece, pieces, plastic, plastic clay, plasticity, plasticizers, positive, potters, property, quartz, quartz inversion, rate, remove, researching, rim, rolled, roller, shrink, shrinkage, slab, slab roller, slabs, slip, slow, sponging, stress, surface, technical, thick, thin, thomas anderson, throwing, tile, tiles, understand, uniform, use, wall, walls, ware, warp, warping, Water, weight, work, writing.

# data[].attributes.attachment_link.title
Great Advice for Preventing Ceramic Warping

# data[].attributes.attachment_link.description
All potters learn early on in their careers that clay has a memory. Clay memory, or clay particle orientation that is affixed by physical/ionic properties, is what can cause ceramic warping. This is because the clay particles tend to return to their initial orientation when they begin to dry out.

# data[].attributes.body
Attempt four 😭😭😭. I had a lot of trouble with the assignment, from flowers stuck in the clay to way too wet clay. I rushed this last attempt to be able to drop something off tomorrow.

# data[].attributes.attachment_caption
I inlaid a fern frond. I'm using twine around the top in hopes of keeping it circular.

# data[].attributes.body
Kurinuki planter or pot w dish. I ordered the ceramic wheel this week, and it makes such a difference!!

# data[].attributes.headline
textured mug - soft slab - art 80 - Zsuzsa Molnar

# data[].attributes.subject
textured mug - soft slab - art 80 - Zsuzsa Molnar

# data[].attributes.body
I wish I can upload a video because there's different designs around the vase. So here is from a different position.

# data[].attributes.body
I carved through the side of my second cup, so I'll have to do it again! Overzealousness with the tools and accurately assessing the state of the clay are two of my biggest struggles right now.

# data[].attributes.headline
ART 80 Pinch Vase Sgraffito - Grace Davidson

# data[].attributes.subject
ART 80 Pinch Vase Sgraffito - Grace Davidson

# data[].attributes.attachment_caption
so heres my firs attempt at sgraffito with my first attempt at a pinch pot. im realizing i messed it up because i used glaze instead of underglaze oops!!

# data[].attributes.headline
Art 80 - Kurinuki 2 - Zsuzsa (Susan) Molnar

# data[].attributes.subject
Art 80 - Kurinuki 2 - Zsuzsa (Susan) Molnar

# data[].attributes.headline
Art 80 - Kurinuki 1 - Zsuzsa (Susan) Molnar

# data[].attributes.subject
Art 80 - Kurinuki 1 - Zsuzsa (Susan) Molnar

# data[].attributes.body
I took inspiration from columnar basalt formations - Jacob Schlegel

# data[].attributes.body
Mackenzie Robertson

# data[].attributes.body
Mackenzie Robertson

# data[].attributes.body
Printable shrinkage rulers. Zsuzsa (Susan)

# data[].attributes.attachment_link.title
Printable pottery shrinkage rulers - Printable Ruler

# data[].attributes.attachment_link.description
Pottery shrinkage rulers are used to determine the shrinkage of wet pottery versus baked pottery.

# data[].attributes.body
I use this a lot, I thought you might find it useful. Zsuzsa (Susan)

# data[].attributes.attachment_link.readable_text
A cone, optionally with the top cut off. (In that case, it's called a frustum). Can be used to help create the geometry for a beaker, vase, party-hat or lamp shade. If you'd like a real cone, just use zero for the top-diameter. Tip: do not score or fold the fold line this template to keep seam smooth.

Support my work:

Advertisment

# data[].attributes.attachment_link.description
A cone, optionally with the top cut off. (In that case, it's called a frustum). Can be used to help create the geometry for a beaker, vase, party-hat or lamp shade. If you'd like a real cone, just use zero for the top-diameter.

# data[].attributes.headline
ART 80 Sgraffito - Zsuzsa (Susan) Molnar

# data[].attributes.subject
ART 80 Sgraffito - Zsuzsa (Susan) Molnar

# data[].attributes.body
I was thinking flowing olive oil, olive branch, and a bowl of "olives"...or ambiguous rounds, haha. I couldn't draw on it with a pencil first. Maybe not dry enough. The amount I felt I was scratching off was more than I anticipated having to.

# data[].attributes.body
I learned the hard way that when the video said stiff leather hard and harder than you think is right, she's not kidding! My piece was clearly more soft leather hard and I ended up taking several huge gouges out of it. I had to scrap my original design and I tried my best to salvage it, but I think my end result has moved way past sgraffito into fluting.

# data[].attributes.headline
Art 82 Pinch Pot Free Study - Mackenzie Robertson (3)

# data[].attributes.subject
Art 82 Pinch Pot Free Study - Mackenzie Robertson (3)

# data[].attributes.headline
Art 82 Pinch Pot Free Study - Mackenzie Robertson (2)

# data[].attributes.subject
Art 82 Pinch Pot Free Study - Mackenzie Robertson (2)

# data[].attributes.headline
Art 82 Pinch Pot Free Study - Mackenzie Robertson

# data[].attributes.subject
Art 82 Pinch Pot Free Study - Mackenzie Robertson

# data[].attributes.body
Jenn Simeone