Pin holes and salvation glaze !

[Evelyne Pensa]

"I'm having trouble with a lovely glaze I used before; I have a lot of pin holes , I refired the plates at a slightly higher temperature 1260°c instead of 1240°c, soaking it longer (30 mns)too but no changes ! I checked and I do have pin holes even with another clay body .
Here's my recipe :
Potash Feldspar 54
Dolomite 18
Quartz 18 
Kaolin 5
Rutile 5
+
Copper Carbonate 1
cobalt carbonate 1

Someone mentionned "salvation glaze" might help ...any information on that ? how could it help ? what's the recipe ?

I'm in France so I translated my "ingredients" but can't give any more references ..

Thank you Evelyne

[Jeff Poulter]

Hi Evelyne,

      I have used this before & it has worked for me.

Salvation Glaze ^6

This recipe was in a pottery magazine a couple of years back and it’s great to fix problems…crazing…blisters, etc.  It WILL change the color of the original glaze, but wow it’s pretty and will fix most problems.

Custer spar              27.0

Gertsley Borate        21.0

Dolomite                      8.8

Talc                           19.5

OM4                            7.5

Silica                           25.2

Cobalt Carb                  3.0

    Mix some up & apply it to your pot that has been heated in the kiln or oven.  Keep the heat at around 100 C. so you don't crack your pot when applying.

[Norm Stuart]

When people in our studio have pinholes in a ceramic fired to ^6,  I tell them to apply a ^06 glaze and fire again to this lower temperature 998C.

The higher percentage of "flux" (fondant pour céramique) in the ^06 glaze mends the surface of the ^6 glaze. I have never seen a ceramic already fired to ^6 give off additional gas at ^06.

"Salvation Glaze" for pinholes at ^10 is a similar concept. It is a very liquid glaze which mends the pinholes.

http://www.potters.org/subject103651.htm

I will make your glaze to see if I get pinholes at 1222C. I don't know enough chemistry to tell you what is causing the gas after soaking it for 30 minutes. I assume an interaction between the glaze and clay.

I do not know enough chemistry to tell you what is causing the gas after soaking for 30 minutes.

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Quand les gens dans notre studio ont piqûres dans une céramique cuite à 6 ^, je leur dis d'appliquer un ^ 06 glaçure et tirer à nouveau à 998C.

L'augmentation du pourcentage de "flux" (écoulement fondant céramique) dans le ^ 06 glaçure répare la surface de l'émail ^ 6. Je n'ai jamais vu une céramique déjà tiré à 6 ^ dégagent du gaz supplémentaire à ^ 06.

Salvation Glaze trous d'épingle à ^ 10 est un concept similaire. C'est un vernis très liquide qui répare les trous.

http://www.potters.org/subject103651.htm

Je vais faire votre céramique-glaçure pour voir si ont piqûres dans céramique à 1222C.

Je ne connais pas assez la chimie de vous dire quelle est la cause du gaz après avoir fait tremper pendant 30 minutes. Je suppose une interaction entre le glaçure et l'argile.

Vous pouvez également remarquer que je n'ai pas assez étudié la langue française.

[Norm Stuart]

I tried your glaze on several clays, with different oxides. They were fired to ^6, with a 30 minute hold, followed by a slow-cool of 28 degrees C between 982 C and 815 C, a six hour period for this temperature range for glaze crystallization.

On the tile below I can see the tiny remains of two pinholes in the top of the tile, where there are 3 coats of glaze. If you use "dark rutile" which is not pre-calcined to remove gas producing components there will be more pin-holes. I used "light rutile" which is calcined.

This variation of your glaze used 1% cobalt carbonate instead of 3%, and 1% copper carbonate.  The original 3% cobalt carbonate did not pinhole at all.