The Woo Yellow Pinhole Experiment

Original Recipe Source: ceramicartsdaily.org/wp-content/uploads/2013/01/33TriedTrueGlazes.pdf

Original Recipe:

Original UMF:

Ceramic Arts Daily:

33 Tried and True Glaze Recipes

(2nd Edition)

What? No boron in a cone 6 glaze?

Examples of Woo Yellow original recipe.Pinholes when glaze is very thick.

No pinholes where thin.

Typical firing temp:Hot Cone 6

Clay body:

Plainsman M340

Type of pinholes:Mainly bubbles contained within the glaze.Most don’t tend to penetrate through to the clay body.

Woo 3

Woo 3 + 4% RIO+ 10% Zircopax

Woo 3 + 4% RIO+ 20% Zircopax

Woo 3 + 4% RIO+ 20% Zircopax

(500g sample)

+ 1 drop of Darvan + 3 drops of Darvan

Woo 3 + 4% RIO + 20% Zircopax

+ 1 drop of Darvan + 3 drops of Darvan

Did Darvan fix the pinholing issue? It’s hard to say. It appears that way, but it could be that the glaze coating is thinner in the 2nd

sample, resulting in less pinholes. Remember, it only pinholes where thick. More testing required.

Woo 3 + 4% RIO+ 20% Zircopax + 1 drop of Darvan(500g sample)

CrackingDuntingShivering

OBSERVATION:

Woo 4

Woo 4 Base

Woo 4 + 4% RIO

Woo 4 + 4% RIO+ 10% Zircopax

Woo 4 + 4% RIO + 10% Zircopax

+ 1 drop Darvan + 3 drops Darvan

Woo 4 + 4% RIO + 10% Zircopax(500g sample)

+ 3 drops Darvan + 4 drops Darvan + 5 drops Darvan + 6 drops Darvan + 10 drops Darvan

10 drops of Darvan didn’t have any significant effect on pinholing

Woo 3 + 4% RIO+ 20% Zircopax

+ DarvanFired in Reduction

Woo 4 + 4% RIO+ 10% Zircopax

+ DarvanFired in Reduction

SAME GLAZES - NO PINHOLESPossible Reasons: Hotter firing?

Longer time between adding of Darvan and dipping of tile – Darvan had more time to incorporate into the mixture?

Woo 8b

Base Base + 10% Zircopax

Base + 10% Zircopax

+ 4% RIO

OBSERVATION: The pinholes don’t show up until we add RIO.This glaze seems to be underfired.

Woo 9

Woo 9 base unfired Woo 9 base Woo 9 plus 4% RIO

Woo 9 + 4% RIO + 10% Zircopax

Woo 9 + 4% RIO + 15% Zircopax

Woo 9 + 4% RIO + 20% Zircopax

Woo 9 base Woo 9 plus 4% RIO

OBSERVATION: Dimpling occurs when RIO is added. Appears to be healed over pinholes.

Woo 9 plus 4% RIO Woo 9 + 4% RIO + 10% Zircopax

OBSERVATION: The pinholes increase when we add zircopax. Is the refractory nature of zircopax raising the melting temp of the glaze?

The bubbles healed over without the zircopax. They didn’t heal over with the zircopax.

Could this be fixed by a longer/hotter firing?

CONCLUSION: RIO seems to be the cause of pinholes in this glaze. The solution to eliminating these pinholes could be simply a hotter or slower firing, giving bubbles more time to heal over. It could possibly be solved by adding more Darvan and/or allowing the Darvan to sit in the glaze longer before testing. More testing is needed before any conclusion can be drawn.