G200 vs G200HP

[Roberta12]

I have been using G200HP for, well, since I set up my studio.  I ordered 20#'s of G200HP and my friends picked it up for me.  As I was adding it to the tubs yesterday, the label says G200.  I called the supply house and asked if they had G200HP and they do not.  And the person I talked to didn't have any info about G200HP.  Here's my first question, Is it not possible to get G200HP now?  Second question, should I make adjustments in my glazes that use G200HP or just mix the 20#s of G200 in to the existing G200Hp and cross my fingers? 

Roberta

[Hulk]

Good question!
Confusing, looks like G200 ran out, replaced by G200HP, which also ran out.

If possible, compare the G200HP component analysis against the material you have now.

There's enough potassium and sodium differences between the G200HP and "Old Blend" to justify small batch testing*, imo.

Digitalfire article:
G200 HP Feldspar (digitalfire.com)

This thread has some history:
Feldspar G-200 - Clay and Glaze Chemistry - Ceramic Arts Daily Community
 

*else limited testing, then look to adjust small amounts if you already made a big batch!

 

[neilestrick]

It depends on what type of glaze it is and how much is in the glaze. I'd run a test first.

[Dick White]

Some feldspar history... G200 was a potash feldspar mined in Monticello, Georgia, but the ore was higher in potassium than other comparable potash feldspars, such as Custer. To resolve this difference, they blended it 70:30 with a soda feldspar brought in from a mine in Spruce Pine, North Carolina. About 15 years ago, the bean counters decided that trucking soda feldspar 300 miles to just to mix it with another feldspar was not economical, so they stopped that. The plain potash feldspar from the Monticello mine was relabeled as G200HP (for High Potassium) and the ceramic industry was advised to mix their own if we wanted to replicate the old G200. Some of us did, some of us bought a product blended by Lauguna and marketed as Old Blend, and others of us moved on to other brands of potash feldspar. About 10 years ago, the Monticello mine was exhausted, and G200HP is no more. The Imerys Corporation (which now owned the mine and product) found a potash feldspar similar to the old blended  product (and other potash feldspars) in Spain and began importing it as G200EU.

So, to answer your specific question - no, you can't buy G200HP anymore (but I know someone who has some). There is nothing else like it on the market that has that high level of potassium. I don't know if you can trust the label of what you just got as actually the old blended G200 that has not been widely available for a long time or maybe is the Spanish G200EU. Because of these nuances, using another brand of feldspar with your remaining G200HP or in place of it is likely to change the way your G200HP recipes turn out. Or you can take a deep dive into some glaze chem software and sort it out from there.

[Min]

Might matter, might not. What's the recipe? 

[Roberta12]

Thanks Tom @Hulk for the link on the 2015 posting.  I did not see that one.  I did see the link to Digitalfire comparing G200 and G200HP.  The person I talked to today, at the supply house, was not knowledgeable about the actual product.  And because I just took what they had in stock (two 10 pound bags, already bagged up and a 5# bag) I do not have a label to look at either.  However, they are a great facility, I will need to talk to one of the owners tomorrow and see if I can find a source for the G200.  It is slightly darker in color than what I have in my tub.  Tomorrow, when I am in the workshop I will pull my G200 recipes and continue this exploration.  Thanks as always for your expert opinions.  @Dick White @neilestrick @Min @Hulk  

R.

[Callie Beller Diesel]

If your supplier is willing to share when they took delivery of the stuff you bought, you might be able to figure out which one it is with this timeline. 

[Roberta12]

I looked at my recipes that use G200hp or what I have been using G200HP in.  There are only 2.  One is MC6 clear which I am not really mixing up any longer (Just mixed a small batch and it is very cloudy on my pieces) and the other is Bright Sky Blue

G200Hp   20

ff3134        20

Wollastonite   10

EPK 20

talc      11.5

silica    18.5

Cobalt Carb  1.0

rutile    6.0

RIO   .5

For Clear I am using a recipe I got from Madeleine or one I got from Naomi Clement.  If I am only using G200 in one glaze, it will be easy to do the testing.  

Thoughts?

[Min]

Given there is only 20 spar in the Bright Sky Blue recipe and I'm guessing you probably have Custer I would just use that in place of the G200-HP. Tiny difference in the sodium and potassium but when added together they total the same in both formulas below. Highly doubt this will make a difference to the glaze.

Round of the numbers to make things simpler. For a 100 gram test batch I'ld round to the tenth decimal point. 

Bright Sky Blue BASE ONLY ^6