Do You Need To Glaze Over Underglaze?

What is underglaze?

Underglaze is a decorative coating used on pottery and ceramics before firing and glazing. It is made from a mixture of clay, colorants, and water that is brushed or painted onto bare clay. Underglaze allows potters to add intricate designs, patterns, and colors to their pieces before they are fired in a kiln.

According to Soul Ceramics, underglazes are made up of 3 main components:

• Clay – Gives underglaze adhesive properties to stick to bare clay surfaces
• Colorants – Oxides, stains, and pigments that provide vibrant colors
• Water – Acts as a binder and allows underglaze to be brushed on

Underglaze serves several key purposes in pottery and ceramics:

• Allows intricate designs not possible with glazes
• Provides brighter, more vibrant colors than glazes
• Goes on smooth and easy for detailed patterns
• Adheres well to greenware or bisque surfaces

Underglaze is typically applied to pottery before the first firing, when the clay is dry but before it has been fired. The underglaze designs then become permanent once the pottery is kiln fired.

What is glaze?

Glaze is a thin layer of material applied to the surface of pottery or ceramic ware. It is usually transparent or semi-transparent and provides a hard, glassy surface after firing in a kiln. Glaze serves several purposes:

• It makes the pottery impermeable to water and other liquids.
• It enhances the beauty of the pottery by adding color, shine, and texture.
• It strengthens the body of the pottery.
• It can hide small flaws and changes to the clay body during firing.

Glazes are usually made from a mixture of silica, fluxes, and coloring oxides. Silica, often in the form of silica sand or flint, provides the glassy quality. Fluxes such as sodium, potassium, and lead lower the melting point of the glaze so it vitrifies at kiln temperatures. Oxides of metals like cobalt, copper, manganese, and iron add color. Glazes may also contain clay, talc, and alumina to improve application properties.

Glazes are applied to bone-dry pottery either by spraying, dipping, or brushing. Multiple layers are often applied to increase opacity and brilliance. The pottery is then fired to over 1200°C to mature the glaze and fuse it to the clay body. Firing melts the glaze ingredients, allowing them to flow together and create the desired surface effect.

Some common types of glaze finishes include gloss, matte, crystalline, and crackle glazes. The ingredients, firing temperature, and kiln atmosphere determine the final look.

Advantages of using underglaze

Underglaze has several key advantages that make it a popular choice among potters and ceramic artists.

One of the main benefits of underglaze is that it allows for more fluidity and flexibility with designs. Underglaze can be painted onto bisqueware in intricate patterns and details that might be more difficult to achieve with regular glaze. The underglaze is soaked into the clay body, allowing artists to layer color upon color to build up complex motifs. According to Soul Ceramics, this makes it possible to “add extra color and detail” to ceramic pieces.

Underglaze is also highly durable. Once fired, the underglaze fuses to the bisque and becomes a permanent part of the clay body. The subsequent glaze firing further stabilizes the underglaze decorations. Pieces decorated with underglaze can withstand repeated use and handwashing without the colors fading or designs wearing away. This durability makes underglaze ideal for mugs, plates, bowls and other functional ware intended for everyday use.

Finally, underglaze is a cost-effective decoration technique. Underglaze colors are concentrated and a little goes a long way. Underglaze also requires only one firing, keeping energy costs low. The ability to reuse leftover amounts also reduces wasted materials. For hobbyists and professional artists alike, underglaze provides an affordable way to add lively, custom designs to ceramic pieces.

Disadvantages of using just underglaze

There are some drawbacks to using only underglaze without any protective glaze on top. According to this Reddit post, underglaze can scratch off over time if not sealed under a glaze. Without a glaze covering it, underglaze is also more prone to fading when exposed to light and air over many years. Additionally, underglaze on its own is porous and can absorb liquids if used on ceramic pieces meant to hold water or food.

Applying only underglaze results in a matte, porous surface that lacks the glossy finish and durability provided by a glaze. So for ceramic pieces that will be frequently handled or washed, using a clear glaze over the underglaze is recommended to protect the decoration and make the surface smoother and more stain-resistant.

Advantages of adding a glaze over underglaze

Adding a glaze over underglaze provides some key benefits:

Glaze protects the decorative underglaze from scratching and wear. According to The Difference Between Underglaze and Glaze, the glaze creates a glassy surface that seals and hardens the piece. Without the glaze, the underglaze decoration could get scratched or damaged over time.

The glaze also seals in the underglaze color underneath. As explained on What Is The Difference Between Glaze And Underglaze, the glaze helps prevent the underglaze from running or bleeding, preserving the original decorative effects.

Additionally, glazing makes the ceramic non-porous and watertight. The glaze forms an impermeable seal so liquids cannot soak into the clay body. This prevents staining, leakage, and absorption issues.

Disadvantages of glazing over underglaze

There are a couple potential downsides to glazing over underglaze that ceramic artists should be aware of:

Glazing over underglaze adds extra time and steps to the overall process. Underglaze can be fired on its own, but adding a glaze requires an additional firing. This extra firing uses more resources in terms of energy, supplies, and the artist’s time [1].

In some cases, layering glaze over underglaze can cause the underglaze to run or bleed, leading to blurry lines or unintended mixing of colors. This happens if the underglaze hasn’t fully matured before applying the glaze, or if incompatible glazes and underglazes are used. Proper firing order and testing material compatibility minimizes running/bleeding risks [2].

Tips for glazing over underglaze

There are a few tips to follow when applying a glaze over underglaze to achieve the best results:

Wait for the underglaze to fully dry before applying the glaze. Underglaze needs to be completely dry or the added moisture from the glaze can cause it to run or blur. Allow the manufacturer’s recommended drying time before adding any layers on top.

Use glazes that are compatible with the underglaze. Some glazes can interact poorly with underglazes, causing discoloration or other issues. Do a small test piece first. Low-fire clear glazes like Amaco Crystal Tex typically work well over underglaze.

Apply multiple thin layers of glaze rather than one thick layer. Build up the glaze opacity gradually. Too much glaze at once can flood the underglaze. 2-3 thin coats are better than 1 thick coat.

Use a soft brush and light strokes when applying the glaze over the underglaze design. Avoid brushing back and forth excessively. Quick, gentle strokes help maintain the crispness of the underglaze.

Allow proper drying time between glaze layers. Rushing the process can lead to crawling, crazing, or pinholes.

Keep the piece steady while glazing to prevent unintended mixing of colors. Tilting can cause the wet glaze to run.

Follow the glaze manufacturer’s instructions for ideal firing temperature and times. Mismatched products or improper firing can ruin results.

When is glazing unnecessary?

Glazing is not always required when using underglaze. According to Underglazes should be applied when?, if the finished piece will not be handled often and is only for display purposes, adding a glaze layer may be unnecessary.

The cost factor should also be considered. As explained on Underglaze | Ceramic, underglazes already provide some shine on their own without an additional glaze. Purchasing and applying glaze adds time and material expenses to the process. For hobbyists on a budget or artists looking to save on production costs, skipping the glaze may be a viable option.

In summary, glazing over underglaze can be skipped if the piece will only be displayed, not touched often, and if limiting expenses is a priority. The aesthetics and purpose of the final ceramic piece should determine if glazing is a required step or an optional artistic choice.

Examples of using underglaze with and without glaze

Underglazes can produce striking results whether used alone or with a final glaze coating. Here are some examples comparing finished ceramic pieces using underglaze with and without an additional glaze:

This vase is decorated with blue underglaze then fired before applying a final clear glaze: https://theartofeducation.edu/2018/05/6-different-ways-to-use-underglazes-with-ceramics/. The glaze helps saturate and unify the colors while providing a glossy surface. Without the glaze, the underglaze would have a matte finish.

These ceramic mugs use black underglaze to create line designs before being fired and glazed: https://www.kness.fr/en/underglazes/. The underglaze remains dark and vivid under the translucent glaze. Without glazing, the lines would blend into the natural terracotta clay color.

In this example, purple underglaze is applied directly onto a bisque fired vase to demonstrate the matte finish: https://www.kness.fr/en/underglazes/. For a brighter glossy surface, adding a protective glaze coating would enhance the underglaze. However, the matte underglaze has an appealing handmade aesthetic.

Showcasing ceramic pieces with and without a final glaze coating illustrates the different visual effects achieved. Glazing over underglaze can intensify colors and add gloss, while using underglaze directly on bisqueware produces a raw natural finish.

Conclusion

In summary, underglaze and glaze serve different purposes in ceramic arts. Underglaze is used to add color and design to bisqueware before firing, while glaze is a glassy coating used to seal and protect finished pottery pieces.

There are pros and cons to using underglaze with and without an additional glaze layer. Key advantages of underglaze include its versatility for adding detailed decorative effects before firing. However, underglaze alone leaves pottery porous and susceptible to staining. Adding a glaze makes pieces functional, watertight and durable for use.

That said, glazing over underglaze can sometimes cause underglaze colors to change or bleed. Proper precautions like using compatible glazes, adding a barrier layer and testing samples help avoid problems.

In summary, glazing over underglaze is recommended for functional ware, but may not always be necessary for purely decorative non-functional pieces. Testing different layering techniques with your particular underglazes and glazes will provide the best guidance on optimal results.