Why does pinholing happen?

Most often: Organic material or carbon in the clay body released gas during glaze firing. Other causes: Bisque firing was too fast or too low to burn out organics. Glaze viscosity too high at maturity to heal over..

Can pinholing be fixed?

Sometimes. Re-fire with a slow approach to peak and a short hold.

How do I prevent pinholing?

Use a slow bisque schedule with a hold at 1100-1400°F to burn out carbon. Hold the glaze firing near peak for 15-30 minutes to let the glaze heal. Add a small amount of flux to a high-viscosity glaze.

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Defect · Glaze firing

Pinholing

Also called: pinholes

Small holes in the glaze surface, typically the size of a pinprick, sometimes with a raised rim.

Appears at: Glaze firing
Severity: Cosmetic
How common: Common

Causes

Most likely

·Organic material or carbon in the clay body released gas during glaze firing
·Bisque firing was too fast or too low to burn out organics
·Glaze viscosity too high at maturity to heal over

Prevention

·Use a slow bisque schedule with a hold at 1100-1400°F to burn out carbon
·Hold the glaze firing near peak for 15-30 minutes to let the glaze heal
·Add a small amount of flux to a high-viscosity glaze

Can it be fixed?

·Re-fire with a slow approach to peak and a short hold

Materials involved

Glaze materials whose chemistry sits behind this defect — each links to its reference page.

Whiting Wollastonite Dolomite Zinc oxide Bone ash

Related defects

Blistering Glaze pitting Crawling

Questions

Why does pinholing happen?: Most often: Organic material or carbon in the clay body released gas during glaze firing. Other causes: Bisque firing was too fast or too low to burn out organics. Glaze viscosity too high at maturity to heal over..
Can pinholing be fixed?: Sometimes. Re-fire with a slow approach to peak and a short hold.
How do I prevent pinholing?: Use a slow bisque schedule with a hold at 1100-1400°F to burn out carbon. Hold the glaze firing near peak for 15-30 minutes to let the glaze heal. Add a small amount of flux to a high-viscosity glaze.

Further reading. The industrial treatment of this defect in the Ceramicware Defects Handbook on Wikibooks (CC BY-SA 3.0).

Sources. Compiled from Claybench's defect reference — the descriptions, causes and remedies that appear consistently across standard ceramics references and studio practice; no single source. It is the same reference the photo diagnosis tool reasons over. Where the Wikibooks Ceramicware Defects Handbook covers a defect it is linked above.

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