21 Essential Underglaze Tips for Pottery

I’m excited to share with you 21 essential underglaze tips for pottery to help you avoid those unwanted surprises when you open the kiln. From mixing your underglaze thoroughly to applying glaze over your design, these tips cover all the basics and provide valuable insights that can enhance your pottery experience.

Whether you’re a beginner or an experienced potter, These small tips can make a big difference and help you achieve better results with your underglaze techniques. So, let’s dive in and explore each one.

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1 Mix Your Underglazes

Even though underglazes are generally stable, always mix them thoroughly before each use to ensure an even consistency and no lumps. You can shake the underglaze in the bottle or stir.

After mixing, pour some into a smaller container so you can check for lumps. If you see any, it’s best to run the underglaze through a Strainer. You don’t want to end up fiddling around with little clumps that got on your brush, in your applicator tip, or on your pottery.

2. Thinning Out Underglaze

If the underglaze is too thick, thin it out with water. Be careful not to add too much water at once; it’s easier to thin it out gradually than to thicken it back up. It is best to use purified or distilled water because you don’t want to introduce minerals from the tap water that may or may not affect the underglaze’s composition.

Plus, my Mister Spray Bottle doesn’t get clogged up with mineral deposits over time. This is something my teacher told me many years ago, so I have always done it with my underglazes and glazes.

3. Thickening Underglaze

You’ll need the underglaze to be thicker when applying it to plastic (workable) clay and leather-hard clay. To thicken your underglaze, leave it uncovered for a while so some of the moisture can evaporate. This process will make the underglaze suitable for decorating.

When I’m in a hurry and can’t wait for the natural evaporation process, I have also used Mayco’s Medium for Silk Screening or block printing. This medium does a fantastic job of thickening the underglaze quickly.

Here is a quick tip: keep a small container of thickened underglaze handy so you’re always prepared when working with different clay stages.

4. Surface Preparation

When applying underglaze to bisque ware, the surface needs to be smooth and clean for the best results. I use fine, wet sandpaper to remove any rough areas. It’s important to wear a Dust Mask if there’s any dust created while sanding.

After sanding, I use a clean, damp sponge to wipe down the bisque ware. This ensures that the underglaze bonds nicely to the surface, giving a better finish. Remember, having a smooth and clean surface is key to preventing any issues during the firing process.

These steps might seem small, but they make a significant difference in how the underglaze adheres to your pottery.

5. Reviving Dried Underglaze

Most commercial underglazes contain pigments like stains and oxides, clay, and frit, which are all minerals. This means they can be rehydrated. Keep in mind, though, that underglazes with organic binders like CMC can degrade. If your underglaze dries out, here’s a quick way to revive it.

Break Up Large Chunks

Place the dried underglaze in a baggie and double it up. Using a hammer, break up any large chunks.

Add Distilled Water

Add a small amount of distilled water to the broken pieces.

Remember, when working with dry materials, dust particles may float around, so wearing a Dust Mask is recommended.

Wait and Mix

Let it sit for about 30 minutes, then mix well. It is best to a mixer or blender for this purpose.

I like to use a Hamilton Beach Blender. It’s small enough to get into most underglaze bottles and powerful enough to blend the underglaze well.

Adjust Consistency

Keep mixing and adding water until you get the right consistency.

It’s reassuring to know that you don’t have to throw your dried underglaze away.

6. Create Test Tiles

Creating test tiles is a smart step for any potter. These small samples allow you to see how different underglazes will appear after firing.

By testing on tiles, you can ensure that the final outcome of your piece meets your expectations. This practice not only saves time and resources but also provides valuable insight into the behavior of your underglazes.

I have a video here showing you How to Make Test Tiles on the Pottery Wheel and Handbuilt.

7. Watercolor Underglazes

To get a watercolor effect on your pottery, it’s best to use bisque ware or even a bone-dry clay body. This method doesn’t work well on wet or leather-hard clay because the underglaze has a lot of water, and the wet clay will not absorb it.

You can make your own watercolors by adjusting the water-to-underglaze ratio. How much water is used depends more on what you hope to achieve rather than the required amount. The more water used, the more transparent the underglaze looks.

You can also buy pre-made watercolors. AMACO has a semi-moist Watercolor Underglaze Set with eight assorted colors.

8. Applying Clear Glaze Over Underglaze

Underglaze by itself is not shiny, so most potters use clear glaze to protect the underglaze, make the colors more vibrant, ensure the piece is food-safe, and give it a glossy, satin, or matte finish. You can use a translucent celadon glaze for a different effect.

Once you’ve created your underglaze designs, you can dip, spray, or brush two to three thin layers of clear glaze over your pottery. Be cautious not to apply too much, as it can cause the pottery glaze to appear milky.

If you apply Clear Glaze to bisque ware with a brush, use a soft brush, and be careful not to apply too much pressure and smudge the underglaze. Some potters will even re-bisque before applying clear glaze just to be safe.

9. The Best Time to Apply Underglaze to Your Pottery

Deciding whether to apply underglaze to greenware or bisqueware depends on the specific results you want to achieve. Greenware is clay that hasn’t been fired yet, while bisqueware has been fired once, making it more stable.

Some Techniques Suitable for Both

Let’s take a look at some popular Techniques and see which ones are suitable to apply to both greenware and bisqueware.

Brushing

Brushing on underglaze is similar to painting. It’s popular for both greenware and bisque-fired clay, depending on preference and desired results. Some potters apply underglaze on greenware to avoid smudging when adding clear glaze to bisqueware.

I prefer applying underglaze on bisqueware, and the color outcome remains consistent whether underglaze is applied to greenware or bisqueware.

Sponging

Sponging is a fun method for applying underglaze. Your underglaze application can be done on both greenware and bisqueware. I prefer to sponge on bisque ware because I like how the sponge pattern adheres to the bisque pieces.

Some potters prefer to sponge on greenware, as they worry that applying it to bisqueware could lead to smudging when the clear glaze is layered over it.

For more detailed information on sponging with underglaze, check out Sponge Glazing | Tips, Tools, And Ideas

Trailing

A slip trailer is used with slip or a denser underglaze to form elevated lines and designs. This method is particularly effective on greenware, which can be adjusted by changing the pressure applied to the Applicator Bottle and the size of the nozzle.

I have found that Slip Trailing with Underglaze on Bisqueware can be successful.

Transfers

When applying transfers to wet or leather-hard clay, the moisture in the clay helps the transfer to adhere smoothly, allowing for seamless integration of the design.

On bisqueware, the process is similar, and though the clay’s absorbency is reduced compared to the leather-hard stage, it can still be done successfully.

Some Techniques Best for Bisqueware

Here are a few techniques that I can only do on Bisqueware

Bubble Glazing

The technique works best on bisqueware because the porous nature of the fired clay absorbs the underglaze effectively, allowing the colors to adhere well and show vividly after the final firing.

The surface of greenware isn’t porous enough to absorb and hold the underglaze, leading to poor adhesion and color display. The moisture in the greenware can also cause the underglaze to run or smear, resulting in a less-defined bubble pattern.

Splattering

Bisqueware provides an ideal surface that absorbs the watered-down underglaze efficiently, allowing for more controlled splatters.

In contrast, applying the same technique on leather-hard clay, can lead to excessive dripping of the underglaze. This is due to the clay’s damp surface causing the watered-down underglaze to flow rather than splatter.

For more information on the Splatter method, you can check out this video, How to Splatter Underglaze on a Mug, a Bowl, and a Plate.

Marbling

For techniques such as the shave cream method or the split cup method, it is best to apply this on Bisqueware. This ensures that the underglaze adheres effectively to the clay’s surface.

To create the marble effect, you can go to Underglazing with Split Cups For a Marbling Effect – A Step-by-Step Guide

Tape Resist

The reason why this process is preferred during the bisque stage, as opposed to the greenware stage, is due to the surface properties of the clay. The greenware stage makes it difficult for the tape to adhere properly, leading to less precise masking.

In contrast, bisque-fired clay provides a better grip for the Washi Tape, ensuring that the masked areas remain clean and the edges of the designs are crisp.

Watercolor Painting

Watercolor painting is best done on bisque-fired clay, as the porous surface of the bisque absorbs the watery underglaze, allowing for subtle blending and gradation of colors, much like traditional watercolor on paper.

Sgraffito is unique and works best at the Leather-hard Stage of Clay. This involves scratching through the underglaze to reveal the clay beneath.

Take your pottery goals and methods into account when deciding on the best time to apply underglaze for your projects. Go to my detailed article Applying Underglaze on Greenware vs Bisqueware to find out which is best for you

10. Applying Underglaze to Wet Clay

Applying underglaze to wet clay can be done effectively by using a thicker consistency. I find it helpful to apply the underglaze either directly onto the clay or onto a piece of transfer paper first. Let the underglaze dry on the paper until it’s leather-hard.

Once it’s ready, transfer the underglaze onto your wet clay. After you’ve applied the underglaze, cover it with plastic to prevent smudging while you shape your clay. This step helps maintain your design and keeps the underglaze from being disturbed.

11. Layering Underglaze

I find it works best to apply underglaze in thin coats on bisqueware or bone-dry clay. The consistency should be like heavy cream. This helps to prevent cracking and peeling during the firing process. I build up the layers gradually, adding more as needed.

For a creative flair, I like to experiment by layering multiple colors. This adds depth to my designs. When I want a thick and raised look, It is best to test on tiles first.

Since underglaze can vary in bonding ingredients, making test tiles ensures the materials are compatible, especially if I use different brands and layer more than four coats.

For more detailed information on layering go to Layering Underglaze?

12. Drying Between Coats

It’s important to let each layer dry completely before adding another coat. The drying time depends on the underglaze thickness and the stage the clay body is in.

On bisqueware and bone-dry clay, the first coat dries rather quickly, allowing you to add the next layer once it’s dry to the touch.

When applying underglaze to wet or leather-hard clay, you’ll need to wait longer, possibly an hour or more, until the underglaze is no longer shiny and dry to the touch before adding the next layer.

I also recommend allowing the underglaze layers to dry naturally. Using heat to speed up the process can cause cracking.

13. Using Liquid Starch

Liquid starch can be added to the underglaze to improve its binding properties and prevent smudging and bleeding. If you choose to use it, keep in mind that starches ferment quickly.

I suggest pouring a small amount of underglaze and Liquid Starch into a separate container. This will help keep the underglaze from going bad or breaking down.

14. Mixing Colors

When creating custom shades, it’s best to mix underglazes in specific ratios. For example, use 1 part of one color to 3 parts of another color. This way, I can achieve the desired shade consistently.

Measuring out the underglazes allows for easy duplication of the unique color you create. If I love a color or run out of it during decorating, it’s much easier to make another batch and ensure that the color matches the previous one. This method saves time and reduces frustration, ensuring that all pieces have a consistent look.

For more detailed information go to How Do You Mix Underglazes / Tips to Mix Underglazes

15. Applying Underglaze to the Bottom of your Pottery

You can apply underglaze to the bottom of both greenware and bisqueware. However, there are some considerations to keep in mind.

Some underglazes might stick to the kiln shelf if applied too thickly. This mainly depends on the amount of frit (silica and flux) in the underglaze and the firing temperature. To avoid this, it’s best to keep the application on the bottom of your piece thin.

If you don’t own your kiln, it’s smart to get approval from your studio before using underglaze on the bottom of your piece. Alternatively, you can use a cookie to Protect the Kiln Shelf. Personally, I have never had my underglaze stick because I always apply it in a thin layer.

You can go to How to Make Kiln Cookies in 6 Easy Steps – With a Video if you want to make them.

16. Prevent Color Transfer During Bisque Firing

Underglaze on greenware should not touch another piece of pottery in the kiln. Underglaze color can transfer onto any pot it is touching. Treat underglazed clay like you are doing a glaze firing, which needs more space in the kiln during bisque firing.

The need for this precaution can vary depending on the brand and thickness of the underglaze. Personally, I never take the risk and always ensure my underglazed pots are separated from the others.

17. Color Changes During Firing

Unlike paints, underglazes look different once fired in the kiln. The color becomes more vibrant. Adding a Clear Glaze can make the colors even more intense.

When firing at higher temperatures, the colors can intensify or darken. Most underglazes can handle high temperatures, like Cone 10, without running because they lack enough silica. Remember, underglaze behaves more like clay than glaze.

Some colors hold better at high temperatures, while others might burn out when fired hotter. Always read the description for each color and test the underglaze at the temperatures you plan to fire to.

18. Sketching with a Pencil

I often outline my designs with a pencil before applying underglaze. This helps to minimize mistakes when painting. You can do this on both bone-dry clay and bisqueware.

Don’t worry about the pencil marks; they will burn off in the kiln, leaving your design clean and precise.

19. Storing Underglaze

When storing your underglaze, make sure the container is airtight to maintain consistency and prevent it from drying out. After each use, scrape any underglaze off the lid. Wipe the lid, The sealing surfaces,

and the threads of the bottle to ensure a tighter seal. This saves time and effort later since you won’t have to spend as much time reviving dried underglaze.

20. Multiple Firings

You can fire a single piece four or even more times in the Kiln to achieve your desired results. It is best not to fire at a higher temperature than any of the previous firings.

Also, be aware that pottery pieces can become brittle if fired over five times. Keep track of how many times you have fired each piece to avoid brittleness.

21. Experimenting with Tools

Trying out different tools and techniques plays a crucial role in developing your unique style. Underglaze, similar to paint, opens up many creative possibilities. Using various tools like brushes, sponges, applicators, and split cups helps to create different effects and textures.

Brushes: Great for detailed work and smooth strokes.

Sponges: Useful for blending and softening edges.

Applicators: Handy for precision lines and small dots.

Split Cups: Perfect for creating layered and marbled effects.

Don’t shy away from trying new methods. Each tool brings out different aspects in your designs, leading to fresh styles and surprising results. Remember, the key is to experiment and have fun!

Conclusion

I hope you found these tips helpful and that they inspire you to get creative with your own pieces. Remember, the key to beautiful underglaze work is practice, experimentation, and having fun.

Using the right materials and techniques can make all the difference. Don’t hesitate to refer to the show notes for any of the supplies mentioned. Keep experimenting and enjoy the process of making beautiful pottery.