Long Time Tried And True Slip Recipe Gone South

[Pottery by Penny]

Hello Fellow mud mashers,

 

I work with Stans red earthenware and decorate it with a basic 4 ingredient slip.  The slip has been perfect for years, now, all of a sudden it is settling like a gooey rock and will not stay suspended.  I cannot for the life of me figure out what has happened, I have not changed a thing.   Here is the recipe:

 25% of each.....EPK, G200, Silica and OM4.  Kinda hard to mess this up.  Could it be a problem with one of the ingredients, It seems as though the prob started when I purchased new silica and EPK.

I cant manage this problem with wholesale orders coming in, especially when I mix colors from the base and they ALL settle.

 

Any help would be soooooo wonderful!!

 

Penny 

 

[Dick White]

Penny, where are you getting the G200? That has not been produced a very long time.

[Mark C.]

A few things

1 is the silica 325 mesh or 200 mesh?

2 Are you now using a G200 substitute ??

 

The EPK is that EdgarsPlastic Kaolin from Florida which has been the same forever-the bags now have an old water tank tower on them.

I have a bag or two of the G200 from a decade or two ago but they have long since changed it to other things

My guess is its one or two?

[Tim T]

If it isn't staying suspended in the glaze bucket, try adding a small amount of epsom salts or vinegar - just add a few drops at a time - and that should help keep things suspended.

[Pottery by Penny]

Penny, where are you getting the G200? That has not been produced a very long time.

Interesting question, I buy G200 from Highwater.

[Pottery by Penny]

A few things

1 is the silica 325 mesh or 200 mesh?

2 Are you now using a G200 substitute ??

 

The EPK is that EdgarsPlastic Kaolin from Florida which has been the same forever-the bags now have an old water tank tower on them.

I have a bag or two of the G200 from a decade or two ago but they have long since changed it to other things

My guess is its one or two?

I do not know the mesh of the Silica and this could be a problem.  The G200 is from Highwater and is labeled as such, it doesnt say substitute, although it would be the same product I have been purchasing so I dont think this would be an issue.

[Pottery by Penny]

If it isn't staying suspended in the glaze bucket, try adding a small amount of epsom salts or vinegar - just add a few drops at a time - and that should help keep things suspended.

I plan on trying this although I really would like to solve the problem, Im kinda weird like that!!

[Dick White]

The original G200 Feldspar was mined in Monticello, GA, but the ore was depleted some 10 years ago. Another feldspar mined in Siloam, GA was similar except for a higher potassium content. It was trucked to the Monticello processing plant and mixed 70:30 with Minspar200, trucked in from Spruce Pine, NC, to recreate the old G200 chemistry. In 2009, the owners made an understandable economic decision to stop shipping the stuff around, and started selling the higher potassium product from Siloam as a new product which they called G200 HP. This was announced and well known in the industry, but many potters didn't focus on the name change and used the new HP product as if it were the old. Or they adjusted without changing their recipe notes for the name/content change. And there are zillions of old recipes floating around calling for G200 and unaware potters would use the new HP thinking it was the same. Also, some suppliers did their own 70:30 blending of HP and Minspar and rebagged it using the old G200 label. In 2013, the Silaom mine was exhausted. In the last year or so, yet another similar potash feldspar has been introduced with the G200 name, this time mined in Spain. It is labeled on the original 44 lb. factory bags as G200EU but often referred to in sales literature or on the smaller re-bagging by vendors simply as G200. So, depending on when you bought it, who you bought it from, and how much detail you went into with the supplier, you could have different stuff.

 

Highwater is selling the EU product, but if you didn't know the back story, you probably wouldn't notice. And from a practical standpoint, the chemistry of the EU product is supposed to be similar to the old original Monticello G200/blended 70:30 G200HP/Minspar, just more expensive because of the shipping from across the pond. But similar chemistry does not always translate to similar performance in the bucket.

 

Mark's suggestion about the 200 vs. 325 mesh of the silica may also change the behavior in the bucket, but without knowing for sure that you previously had one and picked up the other last time without noticing it, hard to say.

 

That leaves us with Tim's excellent recommendation - titrate some saturated epsom salt solution into it a teaspoon at a time to flocculate it for better suspension.

[Min]

does it fire the same as it used to?

 

edit: if you are not buying full bags that are labelled by the mine/plant the material comes from then there is the possibility that your supplier that re-packages might have made an error in labelling. 

[neilestrick]

Are you adding anything else to the slip- deflocculant, colorants, etc?

 

If you're using the same volume of water every time, that could be part of the problem. The moisture level of the dry ingredients can cary greatly, so the same amount of water you usually use may be putting too much water into the mix, causing it to be thinner and settle out. There's also the possibility of the chemistry of your water changing. Try a batch with distilled water and see if it works. Certain stains can cause a deflocculating effect as well. Have your stains changed?

[Pottery by Penny]

does it fire the same as it used to?

 

edit: if you are not buying full bags that are labelled by the mine/plant the material comes from then there is the possibility that your supplier that re-packages might have made an error in labelling. 

Now thats a possibility

[Pottery by Penny]

Wow the information so far has been great.......with that said here are a few variables.

The silica I used on this batch is 200 mesh, the last was 325 BUT previously 200.  So I dont thing that is the problem.

The water could be the issue .....I made a huge batch this time vs smaller batches made prior.  I thought I would save time.  Yeah, Not so much.  

When I broke out the slip into batches and added stain the problem still presented itself so I am looking at the original batch of slip as the problem.  

I am going to attempt the epsome salts tonight and see how it goes.  Tomorrow, I am going to go back to the small batches with the water measured out and see what happens.

 

Whew, what an ordeal 

[High Bridge Pottery]

Have you fired this new batch of slip or mixed up another small test batch, see if it does the same settling? If it does then you can rule out human error but this seems weird, 50% clay doesn't sound like it should be doing all the settling out.

[neilestrick]

Have you fired this new batch of slip or mixed up another small test batch, see if it does the same settling? If it does then you can rule out human error but this seems weird, 50% clay doesn't sound like it should be doing all the settling out.

 

I agree. At 50% clay, it would take either too much water or a deflocculant to get it to settle. Or that EPK isn't EPK but something non-plastic instead. A fired test would tell for sure.

[Mark C.]

Were these full bags your purchased? or rebaged materials sold in smaller quantiles?

I'm a bit confused on the water issue did you add to much water and its settling or is it the same amount of water as usual only a larger batch? which is more water but it still measured?