Tips for fixing skin to make it smooth! Say goodbye to needle marks and blistering skin.

Have you ever? Carefully crafted, decorated, and glazed your work, only to open the kiln and almost collapse at the sight of tiny pinprick-like spots all over, or worse, bumpy, rough surfaces covered in frozen-looking air bubbles.

Today Pottery Clay will delve into the causes and share secret tips to deal with and prevent these problems from ruining our work again.

Get to know the "culprits" that cause problems

Both Pinholes and Blistering are caused by the same reason: gas or air bubbles trying to escape from the clay body or glaze while the glaze is melting.

• If the gas pushes out and the glaze doesn't flow back in time to seal it, it becomes a pinhole.
• If the gas pushes out but the glaze is too thick or viscous, trapping the gas inside, it becomes blistering.

What to do if you find them after opening the kiln?

1.        Re-firing: Place the problematic piece back into the kiln at the same temperature or slightly lower.  However, add the technique of Soaking at the maximum temperature for about 15–20 minutes. This allows the glaze to have time to flow back and smooth out the dry, pitted surface.

2.        Applying glaze to fill deep grooves: In case of very deep pinholes, use the same glaze formula mixed with thick water. Dab or fill the holes completely, let it dry thoroughly, then re-fire.

If you don't want to encounter this again, try this

1. Adjust the "Firing Cycle"

• Increase soaking time: Once the kiln reaches the maximum temperature for that glaze, don't turn off the heat immediately. Instead, hold the temperature constant for about 15–30 minutes. The boiling glaze will gradually settle and flow to create a smooth surface.
• Slow down firing during bisque firing: The temperature range of 700 °C – 950 °C is when most organic matter and carbon gases embedded in the clay are released. If bisque firing is slowed down during this period, the gases will completely evaporate, preventing residual gases from erupting during glaze firing.

2. Adjust "Work Preparation and Glazing Techniques"

• Always wipe dust before glazing: After bisque firing, there's often fine clay dust on the piece. Use a damp sponge to clean it thoroughly, as this dust can trap air during glazing, eventually leading to pinholes.
• Control glaze thickness: Dipping too thickly or in multiple layers (especially with incompatible glazes) can make it difficult for gases to escape, leading to blistering.
• Check glaze consistency: If the glaze is too thick, air bubbles under the glaze won't be able to push through. Water should be added, and the glaze should be sieved to achieve the appropriate viscosity.

3. Adjust "Raw Materials and Chemistry"

• Reduce high-gas-releasing raw materials: In self-mixed glaze formulas, if there is a high amount of Calcium Carbonate (Whiting) or Barium Carbonate, these materials release a lot of carbon dioxide gas during melting. Try adjusting the formula by using Wollastonite or Frits instead to reduce gas formation in the glaze.

For anyone experiencing this problem, we recommend starting with the easiest solution first: try increasing the Soaking time during glaze firing to about 20 minutes in the next kiln run. This method doesn't require changing the clay or glaze formula, but relies on time for the glaze to self-heal. If the surface becomes smoother, you're on the right track!