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Custer feldspar... again... new chemistry 2021 data


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Is anyone having (or aware of) recent issues with Custer feldspar, or aware of any recent independent data on the material content of it? Those who have been in the rabbit hole for awhile may remember maybe 10 years ago, Custer-based glazes suddenly were underfiring. It was a wide enough problem that some folks with access to the necessary resources (e.g., Ron Roy) had samples tested by independent laboratories and found that the potassium content was significantly less than previously, and less than advertised as Pacer Corporation insisted there was no change. Those of us who mix our own glazes and know about such things, recalculated our recipes and got on with our lives. Recently, however, glazes mixed with our last bag of Custer have been running all over the kiln. There has been some slight noise in other clay groups wondering why their glazes with Custer in them are responding differently. We have a pretty smart group of peeps here - does anybody else have any insight?

Edited by Min
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Dick:

Potassium (USA) historically mined in New Mexico (potassium chloride) and Utah (potassium/magnesium). More recently, in Nevada: in proximity to boron/borates. Is Pacer running their own mines, or contractually purchasing from mines? Given the fluidity: would be looking hard at boron (ulexite) contamination. 
 

Tom

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Oh shoot, not again with the Custer. I had seen a few bits here and there that people were having issues with new bags of it but now that you have confirmed it Dick it really does sound like there is another significant change to it. From Pacer's website it looks like they changed ownership in 2018, maybe just maybe they will put out a more accurate analysis instead of having to rely on people like Ron Roy (or like @Kaolinwasher did in 2017, this thread).  Can you use Mahavir until an accurate analysis is found? It's my understanding Custer is mined near Custer, South Dakota.

From Pacer's website the blurb below, I emailed them and asked if they have an updated analysis but I'm not holding my breath.

"In 2018, Pacer Corporation changed ownership and operations management. Under a new name and business philosophy, Pacer Minerals, LLC has improved mining practices, modernized ore sorting techniques, & restructured quality control procedures."

Edited by Min
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Interesting. The company may have been reorganized, but that was 4 years ago. This change in glaze behavior is more recent than that. I too emailed them for an analysis. Most other sources of ceramic material have their analysis somewhere on their website (usually deep, you have to dig and know what you are looking for), but nothing to be seen here.

My local supplier does not carry Mahavir, or I would have been using it all along.

Edited by Dick White
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From Pacer this morning, it's hard to read but the date on the P-325M  is Oct 2020 and on the other is Feb 2021 so neither would be for the current supply. I'm emailing them back and asking if they have more recent ones.

It's interesting to compare this data to Roy's. Even with the Pacer Feb 2021 data compared to Roy's most recent figures there is a "fair" amount of difference in the K2O (up) and Na2O (up). SiO2 down a little and Al2O3 up a little. @Dick White are you using it claybodies too?

767197310_ScreenShot2022-08-16at8_03_38AM.png.e0e1fae26c2cee68142e3f3f1303c075.png1234920946_ScreenShot2022-08-16at8_03_29AM.png.b31cc59d97708e9eeda6cdb06be1f4ef.png

Ron Roy Custer spar analysis from 2012 

360432207_ScreenShot2022-08-16at8_06_56AM.png.c96215c9676af666233ea8e9f6ac4ebf.png

edit: I'm pinning this post, pretty sure this will come up again.

Edited by Min
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Well shoot -I'm almost out of my lifetime supple of Kingman (on last 100# bag) and custar is my next go to. Of course my 2-6 bags are old stock so that may works for some time. Hope you get to the bottom of this -maybe at cone 10 it will not be an issue?

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@Min Interesting! They haven't replied to my request, but when/if they do it will undoubtedly be the same as you received. So, let's go with that. 2020 or 2021 is probably recent enough, it is well after the management change. If we look at the long history and do the numbers: pre-2000ish had 69% silica, 17% alumina, 10% potash, 3% soda (for 13ish% KNa flux) and other miscellany. Ron Roy's average for the early century bags (which is not much different from the numbers @Kaolinwashergot in 2017) had 72% silica, 15% alumina, 7.5% potash, 3% soda (for 10ish% KNa flux) and other miscellany. The new numbers are now almost exactly back to what they were over 20 years ago (and, what pisses me off, what they have been consistently advertising as unchanged during that 20 years of despite different independent material analysis). Actually, the KNa flux now is slightly higher than 20 years ago 14.5% vs. 13.2%, which goes a long way to explaining why my glazes with fair amounts of Custer are now running off the pots. Time to recalculate them again (or more likely, just go back to the old recipes).

And no, I don't mix my own clay bodies, just glazes. But they do in the ceramics program at our sister campus. I will let them know if it matters ,

And now back to work...

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  • Min changed the title to Custer feldspar... again... new chemistry 2021 data
  • Min pinned this topic

It seems that the ore body being mined has changed somewhat. I figure that the tile and paint industries are not having problems with the composition so they dont really give a hoot. I have switched all my glazes that contained custer to the G200eu with no problems whatsoever because of how "dirty"...for lack of a better term custer has become. 

 

2020-09-05 11.34.59.jpg

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