Glaze Shelf Life

[Neil Fallon]

Does material in glaze have a shelf life?  I mixed 5 gallons of Malcolm Davis Carbon Trapped Shino about five years ago.  I had to take a break from gas firing and didn't use the glaze for about three years.  When I was able to fire again (2022),  the results were as expected.  Now the Shino isn't trapping carbon as before.  I know there are many variables to consider. I'm looking at all of them.  The question I have is whether the raw material chemistry could be changing with time?

[PeterH]

12 hours ago, Neil Fallon said:

Does material in glaze have a shelf life?

https://ceramicartsnetwork.org/ceramic-recipes/recipe/Malcom-Davis-Carbon-Trap-Shino-143805#

If the glaze ingredients are (partially) soluble it can cause troubles.

1) Ingredients that dissolve in the water are likely to finish up absorbed in the clay body, rather than remaining at the surface and entering the glaze melt.
Maybe your recipe expected the soda ash to do this, but not the Nepheline Syenite ???
Expert opinions welcomed. <<<

2) If the glaze slop is subject the thermal cycling partially soluble ingredients can cause strange effects.

 

[Bill Kielb]

My experience with carbon trapping, most dependent on the firing cycle. Very fine soot during the cycle readily is trapped, sometimes uniquely because water has randomly splashed on the object which has attracted the solubles to spots on the ware. The mistake I see made most often is in the reduction firing. Generating too much soot in the firing (not good) rather than fine char usually points to poor technique.

[Min]

Everything makes a difference with Shino glazes so yes I would expect something different from the last time you used it. Anything else changed? Claybody, how long you let the pots sit before firing, firing schedule, how you comb you hair etc.

[neilestrick]

Normally I'd say yes, letting it sit for years can cause problems with glazes. Specifically, the level of solubles in the glaze water. However your shino already has a ton of solubles, so I don't think it will be  a big issue. I'd look at the kiln setting first. You won't get good carbon trapping if you didn't create enough carbon or did it too late in the firing. You also need to let the pots dry well, so the salts have time to migrate to the surface.

[Neil Fallon]

Thank you.