Why Use Underglaze Instead Of Glaze?

What is Underglaze?

Underglaze is a ceramic decoration that is applied to pottery or ceramic ware before it is glazed and fired in a kiln. According to Merriam-Webster, underglaze is defined as “a ceramic color or glaze used to decorate an unfired surface.”

Underglaze is used to decorate greenware, bisqueware, or raw clay before a transparent glaze is applied over the top and the piece is fired in a kiln. The colors of the underglaze will remain visible through the glaze after firing. Common types of underglaze include underglaze pencils, underglaze paints, and underglaze transfers. Underglaze is used to hand paint designs, patterns, and images onto pottery or to apply decals before glazing.

According to Collins Dictionary, underglaze refers to “a ceramic color or glaze used for decorating pottery under a transparent glaze before firing.” Underglaze allows potters and ceramic artists to decorate their pieces with colorful imagery and designs before the finishing glaze is applied.

Advantages of Underglaze

There are several key advantages of using underglaze versus glaze on pottery and ceramics:

Underglaze offers artists more control over the design. It can be applied in thin or thick layers using a brush, sponge, or pencil. This allows for finer detail and effects than glaze, which tends to obscure intricacies when applied in thicker layers.

Underglaze also provides access to a wider range of colors than typical glazes. Underglaze comes in virtually any hue, allowing artists to incorporate a full spectrum of colors into their pieces.

Additionally, underglaze has a lower firing temperature than glaze, often by several hundred degrees. This makes it easier to control the finished results without defects like cracking. It also allows underglaze to be used on low-fire clay bodies that would be damaged by higher glaze temperatures.

These advantages give artists more flexibility and make underglaze an excellent choice for detailed, vivid designs on pottery and ceramics.

Disadvantages of Underglaze

While underglazes offer some benefits, there are some drawbacks to using them compared to glazes:

Less durability – Underglazes are less durable than glazes since they do not vitrify and fuse with the clay body. This can make them more prone to chipping or wearing over time. According to ceramic artist Emily Reason, underglazes can rub or scratch off if not properly sealed under a glaze.

Colors can rub off – If not fully sealed by a glaze layer, underglaze colors may rub off onto hands or other surfaces. The pigments in underglazes remain powdery if not vitrified by firing under a glaze.

Multiple firing required – Underglazes must be fired first to adhere to the clay body, then fired again under a glaze to make them food-safe and more durable. This second firing can cause the underglaze colors to shift slightly. So using underglazes adds extra time, effort and firings compared to direct glaze application.

What is Glaze?

Glaze is a vitreous coating applied to pottery to create a glassy, shiny surface finish and seal the porous clay body. Glaze is usually applied by dipping or spraying the pottery form into liquid glaze. When fired in a kiln, the glaze vitrifies and fuses to the clay surface to create a hard, non-porous coating.

Glazes are typically made from a mixture of silica, fluxes, and coloring oxides. The silica provides the glassy quality, while fluxes lower the melting point so the glaze vitrifies at kiln temperatures. Coloring oxides add aesthetic qualities and can create various colors and textures.

Glazes serve both functional and decorative purposes on pottery. Functionally, the impervious glassy surface makes the ware nonporous, so it can hold liquids without leaking. Decoratively, glazes allow for an immense range of colors, textures, and visual effects like cracking or glossiness.

Glazing transforms plain clay into a finished ceramic product with color, shine, and waterproofing. It is the final step before firing pottery in a kiln, where the glaze melts and fuses to the clay body to create the hardened surface finish.

Advantages of Glaze

One of the main advantages of glaze is that it makes finished ceramic pieces much more durable and able to withstand regular use. The glaze creates a glass-like coating that protects the clay body underneath. Pieces glazed with a high quality glaze are extremely hard and resistant to chipping, cracking, staining, and absorbing liquids (source: https://www.thesprucecrafts.com/is-glaze-necessary-for-pottery-2745891). Glazes also make cleaning ceramics much easier since food and liquids do not soak into the clay.

Another benefit of glaze is that the colors are permanent and will not rub off on hands or other surfaces. The glaze melts during the firing process and essentially “stains” the clay body, so the color becomes an integral part of the ceramic. This gives much more vibrant, consistent, and durable coloring than surface techniques like underglaze painting or staining.

Finally, glazing only requires one firing, whereas techniques like underglazing require an additional firing to fuse the glaze. This makes glazing faster and more efficient. The single firing allows the glaze to mature and become glass-like in one step (source: https://ceramicartsnetwork.org/daily/pottery-making-techniques/making-ceramics/ceramics-glazing-and-firing/advantages-and-disadvantages-of-glazes/).

Disadvantages of Glaze

One of the main disadvantages of using glaze is that it offers less control over the final design. Glazes tend to spread and move during firing, making it more difficult to achieve precise decorative effects. Glazing often requires the use of masks or resists to maintain pattern definition.

There are also fewer color options with glazes. Glaze chemistry determines the colors, and it can be challenging to achieve the full spectrum of hues. Underglazes offer more versatility with a wide array of colors that remain true through firing.

In addition, glazes require higher firing temperatures, typically between 2200°F and 2300°F for cone 6 glazes. Underglazes can be fired at lower cone 04 temperatures around 1940°F. The higher heat can increase energy costs and limit the clay bodies and techniques that can be used.

Other disadvantages are that glazes can suffer defects like crazing, crawling, pinholing and shivering. Troubleshooting glaze issues can be complicated and require extensive testing [1]. Underglazes are generally more forgiving and reliable.

When to Use Underglaze vs Glaze

Underglaze and glaze each have advantages that make them better suited for certain applications. Understanding the key differences can help determine when to use underglaze versus glaze.

Underglaze is often preferred when creating detailed designs on ceramic pieces. The velvety matte finish allows underglaze to showcase intricate patterns and small details. Underglaze can be painted on in multiple layers to blend colors and build up dimension. This makes it an excellent choice for adding complex decorative elements like flowers, animals, landscapes, and lettering ^[1].

Glaze is better for functional ceramic pieces that require a durable, non-porous surface for uses like food service and drinkware. The glossy surface created by glaze provides an impermeable coating that holds up to frequent use and washing. Glazes are also often preferred for sculpture, as they unify the look and enhance the form ^[1]. So for mugs, plates, bowls, and decorative sculptures that need to withstand handling, glaze tends to work better than underglaze.

For most ceramic projects, a combination of underglaze and glaze is ideal. The underglaze creates detailed designs that are then sealed and protected by an overlying glaze. This takes advantage of the best attributes of both materials. But when deciding between one or the other, consider underglaze for artistic creations with intricate details, and glaze for functional ware needing durability.

^[1] https://www.unexpectedlullaby.com/blog/how-to-paint-ceramics

Underglaze Design Techniques

Underglaze offers many exciting design techniques for pottery. You can create intricate designs by painting, stamping, stenciling, and more. Layering colors is also a popular technique with underglaze. Here are some key techniques:

Painting freehand with underglaze allows you to create flowing, artistic designs. Use different sized brushes for bold strokes or intricate details. Underglaze painting works best on bisqueware rather than greenware since it absorbs better after the first firing.

Stamping with rubber stamps or carved blocks is an easy way to repeatedly create patterns. Press the stamp firmly into the underglaze to transfer the design. You can stamp on greenware or bisqueware.

Stenciling involves using a pre-cut stencil with underglaze. Hold the stencil firmly against the surface and apply underglaze with a brush or sponge on top. Lift the stencil straight up to reveal the crisp design. Stencils allow you to recreate designs quickly.

Sgraffito involves scratching through one layer of underglaze to reveal a different color underneath. For example, you can coat a piece with black underglaze and scratch a design through to expose the bare clay. Sgraffito creates striking contrasting designs.

Layering underglaze colors allows you to create depth and patterns. For example, paint broad stripes in different colors, then use a damp sponge to softly blend the edges. Or paint dots in one color and let them dry before adding dots in another color on top.

Glaze Techniques

Glazing is an essential finishing step in pottery and ceramic work. There are various techniques for applying glaze to bisqueware to achieve different artistic effects.

Popular glaze application methods include:

– Dipping – Fully submerging an item in a bucket or vat of glaze. This evenly coats the piece in glaze. Dipping works best for smooth surfaces without intricate details.

– Pouring – Carefully pouring glaze over a piece to control coverage and allow glaze to pool in certain areas. This creates fluid, dripping effects. Pouring works well for intricate surfaces.

– Spraying – Applying glaze through a spray gun or atomizer. This allows for a thin, even misting of glaze. Spraying can create soft color gradients. It works for covering large areas evenly.

Proper mixing is crucial for glaze techniques. Follow manufacturer instructions when mixing powdered glaze with water. The glaze should have a creamy, liquid consistency. Make sure to stir thoroughly to fully incorporate powder. Test glaze on a tile before applying to artwork.

Experiment with dipping, pouring, and spraying glazes on test pieces to get comfortable with application. Glazing takes practice to master how glaze moves over bisque surfaces. Be patient and have fun exploring different glazing techniques. For more tips, refer to this article: https://potterycrafters.com/glazing-pottery-dip-drip-and-brush-pottery-glazing-tips/

Conclusion

In summary, the key differences between underglaze and glaze are:

• Underglaze is porous and needs a clear glaze applied on top for protection. Glaze is non-porous and provides its own protective coating.
• Underglaze can be used on greenware and bisqueware. Glaze can only be used on bisqueware.
• Underglaze is used for decorative techniques like brushwork, hand painting, and stamping. Glaze provides an even, shiny coating.
• Underglaze has a matte finish after firing. Glaze has a glossy finish.

Underglaze is best for decorative techniques on greenware or bisqueware before applying a final clear glaze. Glaze provides a smooth, protective finish and is ideal for simple, monochromatic pieces. Use underglaze when you want to hand decorate a piece with textures, patterns, illustrations, words, etc. Use glaze for an even, shiny coating without decoration.