Thursday, June 16, 2011

Glaze Conundrum 2011

This year has been a tough one for me and my glazes... I don't know what is going on, but several of my trusty, dependable glazes have decided they will no longer cooperate. Take a look:

1. Pharsalia Green then...
Here's my Pharsalia Green glaze. I've had this glaze for over 12 years (15?) and I've always loved it. It's from Richard Zakin's Electric Kiln Ceramics (1994 edition, page  124). This is what it used to look like (photo 1)... Nice, right? This is what it looks like now (photo 2).

Something in one of the ingredients, you say? I checked... I made a new batch just in case I had made a mistake... nothing... I can't get back to my old Pharsalia Green no matter what I try!

2. Pharsalia Green now...
Maybe it's the firing, you say? Maybe... but I'm not doing anything different AND the "sister" glaze: Pharsalia Blue is doing just fine, thank you!

Another glaze that's breaking my heart is the old Randy's Red. I got that recipe so long ago that I can't even remember when or from whom. But it was a beautiful, reddish brown glaze that broke to blacks and golds. Now it's just a mucky old brown with nothing happening, no breaking, no gorgeous color, nothing... Here is Randy's Red before (photo 3) and after (photo 4).

Both of these glazes have Gerstley Borate in the recipe. The Pharsalia glaze has 10% and Randy's has 31%... They also both use soda feldspar... 30% for the green glaze and  20% for Randy's Red.

3.Randy's Red then...
And I've got a couple other "old" glazes that are also failing.

The one thing the failing glazes have in common is that the raw glaze on a pot feels dry, rough, thin rather than powdery and smooth.

A sad state of affairs...

 Fortunately, in the meantime I have been experimenting with glazes from the Mastering Cone 6 Glazes book and have got great results with slate blue, oatmeal, and spearmint... and now with the new Selsor yellow.... I think I'll just forget about the old glazes.

4. Randy's Red now..
Any thoughts on my conundrum will be appreciated it.


Linda Starr said...

Is there a common ingredient in these glazes that could have changed suppliers or where it is mined? What about the water you use to mix the glazes, could that have changed. Do you have a well? I ask about the well since we needed a new pump recently and there was lots of iron in our water before that, although I use either distilled or spring water for mixing my glazes. Are you using cones on every shelf and has the firing changed at all on any shelves? both the red and green are super glazes it would be a shame to give them up.

Gina said...

I know the frustration of having a favorite glaze no longer do what it used to do. I was thinking along the same lines as Linda in that perhaps your glaze ingredients are slightly different, or your clay has changed in some way. Have you changed your firing schedule with a longer or shorter hold, quicker cool down, etc? Different glazes in the kiln with these ones? Good luck finding the fix and with your new glazes.

Darlene said...

I was also thinking about the firing schedule. If the kiln is cooling faster, that could account for the change in Randy's red. Also Gerstley Borate can be pretty variable - did you just get a new bag perhaps?? Gerstley is good for creating a hard surface on the pots before firing, so I also wonder if this could be connected to your results.
Hope you figure it out!

Darlene said...

Another thought. Could it be one of your materials is settling out a bit more than usual?? I remember when there was a change in copper a few years back and it started settling out in my glazes driving me crazy! You may try glazing something immediately after sieving, and then try something 15 minutes later and see if they are different.