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

Have you ever? You diligently molded, decorated, and glazed your work, only to open the kiln and feel devastated because the piece was full of tiny pinprick-like spots, or worse, had bumpy, rough surfaces like frozen air bubbles all over it.

Today Pottery Clay will delve into the causes and share secret tips to handle and prevent these culprits from ruining your work again.

Understand the "culprits" causing the 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 cover it, it will result in pinholes.
• If the gas pushes out but the glaze is too thick or viscous, causing the gas to get trapped inside, it will result in blistering.

What to do if you open the kiln and find this?

1.        Re-firing: Place the problematic piece back into the kiln at the same temperature or slightly lower, but add a Soaking technique (holding the temperature) at the peak temperature for about 15–20 minutes to allow the glaze to flow back and smooth out the sunken areas.

2.        Applying glaze to fill deep grooves: For very deep pinholes, use the same glaze formula mixed with thick water. Dab or fill the holes, let it dry completely, then refire.

If you want to avoid this problem again, try the following:

1. Adjust the "Firing Cycle"

• Increase soaking time: Once the kiln reaches the peak temperature for that glaze, don't turn off the power immediately. Hold the temperature steady for about 15–30 minutes. The boiling glaze will gradually settle down and flow to create a smooth surface.
• Slow down the firing rate during bisque firing: Between 700 °C and 950 °C, organic matter and carbon gases embedded in the clay are most actively released. If this bisque firing stage is slowed down, all gases will evaporate, preventing residual gases from erupting during the glaze firing.

2. Adjust "work preparation and glazing techniques"

• Always wipe off 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: Applying glaze too thickly or in multiple layers (especially different glaze types) makes it difficult for gases to escape, leading to blisters.
• Check glaze consistency: If the glaze is too thick, air bubbles under the glaze won't be able to break through. Mix water and sieve the glaze to achieve the right viscosity.

3. Adjust "raw materials and chemistry"

• Reduce high gas-releasing raw materials: In a self-mixed glaze formula, if there's a large amount of Calcium Carbonate (Whiting) or Barium Carbonate, these materials release a high amount 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 currently facing this problem, I recommend starting with the easiest solution: try increasing the Soaking time to about 20 minutes in your next glaze firing. This method doesn't require changing both the clay and glaze formulas but relies on giving the glaze time to heal itself. If your work's surface becomes smoother after doing this, then you're on the right track!