Does "Copper" in Pottery Turn Neighboring Pieces Red? Glaze Knowledge to Avoid Failures in the Classroom

Introduction: To prevent that "Uh-oh" moment when opening the kiln

Have you ever had an experience like this when using glazes containing copper, such as Oribe or Shinsha (Copper Red) in a pottery class?

"My neighbor's pure white pot has faint red spots on it..."
"The teacher told me to 'be careful where I place pieces with copper,' but I don't really know why."

Actually, this is not your mistake. It is a phenomenon specific to "Copper" occurring inside the high-temperature kiln.

This time, for those of you who want more than just the classroom glazes and are looking for your own colors, Fukaumi Shouten will explain the behavior of "Copper," which is tricky but fascinating, in an easy-to-understand way.

1. Why does color transfer without touching? The Mystery of "Volatilization"

In the world of pottery, copper is a popular metal that produces vivid greens and reds. However, it has a slightly tomboyish nature of being prone to "Volatilization" during firing.

Drama happening inside the kiln

When the kiln temperature exceeds 1000°C, some of the copper components in the glaze turn into gas and float away from the piece.

What happens when this gasified copper falls onto nearby white porcelain or white glazed pieces?

1. Adhesion: The copper component adheres to the surface of the neighboring piece.
2. Coloring: In the case of reduction firing (firing that robs oxygen), the attached trace amount of copper reacts chemically and develops a Red color (Shinsha color).

This is a phenomenon called "Colloidal Coloring", where copper nanoparticles absorb specific wavelengths of light, appearing as a beautiful red color to our eyes.

In other words, it's as if your passionate red color unintentionally flew over to your neighbor's piece and faintly "blushed its cheeks". To prevent this, you need to correctly understand the properties of copper.

2. Manners and Influence on "Kiln Shelves" you should know

Copper volatilization affects not only the space but also the "tools". You should be especially careful about the "Kiln Shelf" on which you place your work.

Invisible memories remain

Kiln shelves look pure white at first glance, but volatilized copper adheres to these shelves as well.

What happens if you use a shelf with copper attached to fire a "piece without copper" next time?

In the kiln that has become hot again, the copper sleeping on the shelf wakes up (re-volatilizes) and may transfer to the new piece.
"I didn't use copper, but copper coloring is seen here and there..."
The cause is often in the memory of past firings.

When using a classroom or shared kiln, this is an important point regarding manners.

3. "Solutions" to avoid trouble and express freely

"I'm afraid of causing trouble, so maybe I should stop using copper..."
There is no need to think so. With correct knowledge and countermeasures, you can enjoy expression more freely.

① Use a "Sagger (Box)" — Your own private room

The most reliable method used by professionals is to fire it in a lidded container called a "Sagger (Saya)" or "Boshi".
This way, even if the copper volatilizes, it stays inside the sagger, so there is no worry of contaminating neighboring pieces or kiln shelves. It's like consideration to close the door of a private room when burning incense.

② Peace of mind with Fukaumi Shouten's "Ingredients Indication"

And what is most important is to "know what is in the glaze you are using".

Some commercially available glazes have unclear ingredients. To prevent sad accidents where you unknowingly use a glaze containing copper and cause trouble...

At Fukaumi Shouten, we always state "Contains Copper" for glazes containing copper.

• "This glaze contains copper, so I'll use a sagger."
• "I'll tell the teacher 'It contains copper, so I want to consult about placement'."

If you know the ingredients, you can confidently take measures and become a "step-advanced potter" who can also be considerate of others.

Summary: Knowledge becomes your kindness

Pottery is an art of chemical reactions. Just knowing "why it happens" changes anxiety into "confidence" and failure into "consideration".

Fukaumi Shouten delivers high-quality paints and glazes that clarify whether they contain copper so that you can create with peace of mind.

Fukaumi Shouten supports your creativity and consideration.

FAQ: Handling Copper Glazes

Q. Why does color transfer to neighboring pieces in pottery?

A. This is because metal components such as copper gasify (volatilize) due to high temperatures in the kiln and adhere to and react with neighboring pieces. Copper in particular volatilizes easily, causing phenomena where white porcelain turns partially red.

Q. How can I prevent copper glaze volatilization?

A. Firing in a lidded container called a "Sagger (Saya)" is the most reliable method. It is also effective to decide on shelves or kilns specifically for copper.