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Member Since 15 Feb 2013
Offline Last Active Yesterday, 08:20 PM

Topics I've Started

Why Calcine China Clay?

26 June 2017 - 07:51 PM

Okay another possibly stupid question....

Why would you Calcine China Clay?

Background: I found a plastic bin marked, China Clay (calcined), in the storage room this past weekend at the art center and am wondering what it is used for and why it was calcined, etc. the little research I did seemed to suggest it helps prevent crawling of certain glazes.

Quote: " Raw kaolin also supplies suspension to the glaze slurry and it hardens the dry glaze layer. However once raw kaolin percentages pass 20% in a recipe shrinkages can be to high (causing crawling). In these cases substituting part of the raw kaolin for calcined material solves the problem, maintaining the chemistry of the glaze but reducing the shrinkage and cracking. In other words, by substituting some of the raw kaolin for calcined the physical properties of the glaze slurry can be controlled without impacting the chemistry of the fired melt. Of course, mixing the raw and calcined materials must take into account the LOI of the raw material (12% less calcined is needed)."

So far none of the recipes that I have found call for calcined China Clay... so if you need this is it normally recorded in the recipe or are you just kind of supposed to know?

Thanks again!


Is There A Substitute For Plastic Vitrox?

24 June 2017 - 03:01 PM

I have a recipe and it calls for Plastic Vitrox. Is there a substitute for this? GlazeNerd to the Rescue?

Plastic Vitrox - 54%
Gerstley Borate - 46%
Colbalt Barb - 3%
Copper Carb - 1%

If I have to special order the Plastic Vitrox I will but I am hoping I can substitute with the more common ingredients that I have already.


A Question About Talc

18 June 2017 - 07:51 AM

I have a recipe that calls for Talc.
I have a container of Texas Talc.

Is it the same thing?


Plastic Vitrox, Aka Pv Glazes?

11 June 2017 - 08:12 PM

In starting my glaze research and continuing my glaze education I came across PV: Plastic Vitrox.
2 of the glazes at the art center are called PV Blue and PV Green, I am assuming they are made using Plastic Vitrox. Everything I have read on it though seems to suggest it is used in clay bodies not glazes so am I researching the wrong thing for PV glazes?

All you wonderful glaze nerds out there can you give a girl a little education in this?

Also, is it something I should be stocking in my glaze mixing pantry?

Thanks so much!


Magruder Red... Been Told It's Touchy

10 June 2017 - 03:58 PM

Hi all
There is a bucket of something called Magruder Red at the Art Center. I've been told it's touchy to fire, that I have to fire only Magruder Red pieces together in the kiln to a cone higher than the kiln is usually fired. I've yet to fire any pieces as there are only a couple waiting to be fired.

My question is... why is it touchy and is there a way to fire it with other pieces in the same kiln to the same temperature. This separate firing is a pain as I have to essentially store the pieces until I have enough to fill a whole kiln. I also asked, what if someone uses it with another glaze do I fire it to the regular cone or the higher and if to the higher what happens with the other glaze? I got no answer to this. Personally I'd just as soon jettison it but some like its iron red coloring. Can anyone recommend a glaze to take its place?

Yeah I know more than one question here but any help or pointers in a direction to look would be appreciated.