Why Does My Glaze Look Different? 6 Causes & Solutions by Experts | Fukaumi Shouten

[Pottery Mystery] Why Doesn't My Glaze Look Like the Sample? 6 Causes & Solutions

"The glaze color is completely different from the sample..."
Every potter experiences this at least once or twice.

"Is it a defective product?" Before you doubt the material, let's look at the chemistry happening inside the kiln.
In fact, glaze color is like a "living thing" that changes drastically.
Even with the same glaze, changing just one condition—clay, temperature, thickness, or cooling—can result in a completely different expression.

This article explains the "6 main causes" why your work differs from the sample, with easy-to-understand diagrams.

1. Different "Clay" Means Different Colors

Glaze does not just "sit" on top of the clay. When melted at high temperatures, the glaze chemically reacts and integrates with the surface of the clay.

• Red Clay / Stoneware: High in iron and impurities, which react with the glaze, often making colors darker or more muted.
• White Clay / Porcelain: Low in iron, allowing the glaze's original vivid colors to show through.

"The sample was on white clay, but it turned muddy on red clay." This is exactly the result of the clay's components reacting with the glaze.

2. Cooling Time Changes Crystal Size

After turning off the kiln, "how fast it cools down (Slow Cooling)" dramatically changes the size of crystals generated within the glaze.
This is the same principle as the "recrystallization of salt" learned in elementary school science.

Especially with crystalline glazes, if "the large crystal patterns didn't appear like the sample," the cause is often that the cooling speed was too fast (not enough time for crystals to grow).

3. "Density" Changes the Color

The "Baumé degree (Specific Gravity)" of the glaze is also critical. It shouldn't be too thin or too thick.

• Appropriate Range: Generally around Baumé 40° to 55°.
• Too Thin: Colors won't show, resulting in a weak finish.
• Too Thick: Likely to cause "crawling" or "cracking" during firing.

4. "Clay Thickness" Affects Glaze Thickness

Surprisingly often overlooked is the thickness of the vessel (body) itself.
Bisque ware absorbs water like a sponge.

• Thick Vessel (Thick Sponge): Absorbs a lot of water, so a thick layer of glaze adheres.
• Thin Vessel (Thin Sponge): Water saturates quickly, so only a thin layer of glaze adheres.

Even if dipped for the same number of seconds, if the thickness of the vessel differs, the amount of glaze adhering (and thus the color intensity) will change.

5. "Firing Temperature" Changes Melting

Simply put, "Fire it well, and it melts well."
The firing temperature directly affects the degree of vitrification (melting) of the glaze.

• Low Temperature: The glaze doesn't melt fully, becoming matte, rough, or milky.
• High Temperature: The glaze melts thoroughly, becoming glossy and fluid.

Also, a difference of just "±30°C" can significantly change this melting behavior.

6. Temperature Unevenness by "Kiln Location"

"I fired them in the same kiln, but the colors are different on the top and bottom shelves."
This is due to the temperature distribution (heat curve) inside the kiln.

• Top: Heat rises, so it generally gets hotter, and glazes melt well.
• Bottom: Temperature tends to be lower, which may lead to under-firing.

Even in electric kilns, unevenness occurs depending on the position of the heating elements. For important pieces, you need to know your kiln's "habits" when placing them.

Summary: Enjoying the Difference is the Joy of Pottery

"Differing from the sample" is not necessarily a failure.
It is a unique color in the world created by your kiln, your clay, and your application method.

However, "testing" is essential to achieve the targeted color.
First, try using small test pieces to see what color you get in your environment.
Accumulating that data will turn you into a "magician of color."