"Underglaze, In-glaze, and On-glaze": Choosing the Right Ceramic Decorating Technique for Your Project

For those new to ceramics or looking for decorating techniques, you may have heard the terms Underglaze, In-glaze, and On-glaze, but are unsure about their differences and which type of work they are suitable for. Today, Pottery Clay will tell you all about them.

All three techniques use "color" to decorate ceramic pieces, but the crucial difference for ceramists is the timing of color application, the position of the color after firing, and the resulting surface finish, which directly affects the practical use of the finished piece.

1. Underglaze

This involves applying color to the piece before clear glazing. The color is sealed beneath the glaze layer after glaze firing, making the patterns highly durable, resistant to peeling, and not easily worn out from use.

The process begins with shaping and decorating the piece > Bisque Firing > Applying Underglaze > Applying clear glaze > Glaze Firing.

The advantages of underglaze work are:

o    Excellent durability against wear and scratches.

o    Safest and most suitable for actual food and beverage containers.

• Easy to draw patterns, details, and illustrations, with the ability to achieve light and dark shading like a drawing.
• It is the number one popular technique in contemporary ceramic studios.

2. In-glaze

This is an expert-level technique where color is sprayed or painted onto an unfired glaze layer, or colors are used that will melt and merge with the glaze layer during firing. This results in highly durable colors with a beautiful and unique dimensional depth.

There are many advantages, including:

• The color melts and permanently integrates with the glaze layer.
• Smooth, seamless surface finish, highly resistant to chemicals and abrasion.
• Provides a soft and deep color dimension within the glaze.

For In-glaze, it's important to note that potters must precisely control the temperature and atmosphere in the kiln. The range of colors that can withstand such high temperatures is more limited than other techniques, so it is mostly found in traditional porcelain and industrial production.

3. On-glaze or Overglaze

This involves applying color or decals after the piece has been glazed and glaze-fired. It is then refired at a lower temperature to adhere the color firmly to the glaze surface. This technique is considered premium decoration due to its vivid, vibrant colors and the ability to use special materials.

The process begins with a fully glaze-fired piece > On-glaze application, including gilding > Refiring at a low temperature.

The advantages of using underglaze colors are:

• The most vivid and sharp colors, as they don't undergo high temperatures that degrade the pigment.
• Excellent for capturing fine and delicate lines.
• Supports advanced decorative techniques, such as applying genuine gold, silver, or luster that provides a pearlescent shimmer.

However, On-glaze work has a limitation: it is less resistant to abrasion and chemicals than other methods because the color is on the outermost layer of the glaze. It is more suitable for decorative or display pieces rather than items that require frequent washing and scrubbing.