Looking for a dry-mix recipe to fix plasticity in my mid-fire porcelain clay.

[Clay-Tooth]

Hi everyone,

I’m working with Laguna WC-617 porcelain and primarily use it on the wheel, though I also do some hand-building. My reclaimed clay, which goes through a de-airing pugmill, is often and persistently short and crumbly. My usual method of adding throwing slip hasn’t been effective in improving its plasticity. 

Sometimes I get a decent batch through, but honestly it feels like a fluke when I do! I think my most recent success was a batch of reclaimed clay where I added in some slip from an old bucket that had sodium silicate added to keep it suspended. However, I don’t remember the exact details, and I’m unsure if sodium silicate was a factor or if it could harm the final product.

I’ve been researching ways to enhance plasticity with dry materials but feel overwhelmed by the information. I know I will need to do some testing (unless anyone has solved this same problem with Laguna WC-617!), I’m just hoping to avoid taking stabs in the dark. I welcome any starting points or specific recommendations that have worked for others.

Here is the info from the SDS sheet for Laguna WC-617:

• Kaolin: 25-65%
• Crystalline Silica (Quartz): 10-25%
• Feldspar: 10-25%
• Nepheline Syenite: 5-10%
• Bentonite: <2%
• Smectite Clay: <2%
• Titanium Dioxide: <2%

For context, my clay was previously frozen, and I’ve fully rehydrated it before pugging. I also mix in a bit of speckled stoneware and sometimes add manganese for desired speckled effect, but I have not found these to specifically affect plasticity one way or another. I think I'm just getting a higher ratio of clay that's been thrown multiple times and it's gradually degrading in plasticity. Because I have to dry out and rehydrate the once-frozen clay, I can't just quickly and easily mix in fresh clay, either. And the cost and volume requirements to purchase the dry mix version are absolutely prohibitive for a solo artist.

I’m looking for practical advice or tested formulas from anyone who has faced similar issues with this clay. I’ve checked the SDS sheet for the clay, but specific ratios are proprietary.

Thanks in advance for any help!

Caroline

Edited August 23 by Clay-Tooth
typo

[Clay-Tooth]

[Hulk]

Hi Caroline,
Welcome to the Forum!

A long time Forum member had suggested a "reclaim mix" - mentioned here, third entry:
Verticals cracks shortly after throwing - Studio Operations and Making Work - Ceramic Arts Daily Community

Excerpted from a similar thread:
"A small amount of Nerd's reclaim mix makes a noticeable difference in four to five gallons of reclaim slurry, in my experience.
I'd tried between a quarter to third cup of the recommended mixture, one part silica, eight parts OM4 ball clay, one part feldspar.
Now I'll use it if the reclaim contains significant amounts of re-reclaim and/or re-re-claim..."

 

Doesn't take much to alter the reclaim's behavior!
...noticably more plastic, takes longer to dry.
I'm not seeing any noticeable changes in clay's appearance, glaze interaction, porosity, et cetera, after the addition.
Be sure, however, to test thoroughly!

I haven't used any over the last year or so, as my reclaim batches have contained a lot of new clay...
 

Note: the original excerpt had the proportions reversed!

Edited August 23 by Hulk
test, test, test! check and edit link

[Clay-Tooth]

This seems like a fair place to start. I would guess that since the recipe of the clay contains Kaolin and not Ball Clay, I should sub those two in Nerd's reclaim mix recipe. I wonder if it matters which feldspar is used? 

[Hulk]

Somewhere in the discussion, EPK was mentioned as an ingredient that does not improve plasticity.

I believe I've used Custer - the only feldspar I have other than nepheline cyanate and petalite.

Here's an article, more depth and detail:

Clay Restoration (ceramicartsnetwork.org)

[Min]

If you want to keep your grolleg porcelain white I wouldn't add ball clay to it. Kaolins are not as plastic as ball clays, that is why a plasticizer is added to kaolin only porcelain bodies. Given that you have been able to add slip to your reclaim I would suggest making a slurry of Bentone MA (previously known as Macaloid) and adding approx 1/2 - 1% dry weight of that to your reclaim.

If you guessitmate the pugged body to have approx 20% water content and you know the rough output of your pugger you can math out how much to add. Bentone MA definitely cannot be added dry to the reclaimed clay, it must be thoroughly wetted prior to adding it to the clay. 1/2 -1% Bentone MA could be enough to add to your reclaim. Might need a titch more or less but it would be a place to start. It is expensive but works brilliantly.

What I have done is sprinkle it onto hot water then use a stick blender to mix it. Mix until you have a thick mass then mix it again. Go for at least 30 minutes of blending, might have to add more water to get a smooth creamy mix, what you are aiming for is a yogurt like consistancy.  Add the Bentone MA slurry gradually to your pugger then run the clay through a couple more times to ensure it is well blended into the clay. If you have a mixer pugger then even better to get it incorporated.

Another point is to have enough water in your reclaim, sometimes just having the clay a bit too dry will make it short. (water of plasticity)

[neilestrick]

Every time you recycle it you're changing the formula a bit, especially if you start adding things to the mix. I'd definitely run some absorption tests and make sure your reclaim is still where it needs to be in terms of vitrification. However for me the big questions is why are you spending money on a grolleg porcelain, which is the most expensive and least plastic of all clay bodies, if you're mixing it with a speckled stoneware? I'd look for a smooth white stoneware or a domestic porcelain that has ball clay. It'll be cheaper and be more plastic. There's no reason to spend all that money on something pure white if you're adding stoneware to it anyway.

[Clay-Tooth]

@neilestrick This is a good point about the cost of the clay. To be honest though I am early enough in my career I haven't fully decided even what color clay body I ultimately want to work in. This clay I have been using I purchased at 40 cents/pound from a friend who had been storing it, and that's influenced my decision more than almost anything. You're right though, if this smooth but speckled white is the way I want to go I could look for, at minimum, the cheapest mid-fire porcelain or the least grogged white stoneware clay body when I run out of this clay. I've been confused about the term grolleg though, and how to determine whether or not a clay has it when it's not in the name or ingredients.

@Min thanks for the recommendation and instructions on using BentoneMA. I was able to track some down online through KY Mudworks. And @Hulk thanks for your advice and getting me to that article! 

Now to determine how to best run some tests without filling and mixing up a whole pugger worth of clay (about 25#). I hope to do some tests going forward with some smaller amounts of clay wedging in these fixes the best I can. We'll see if that works...

[Hulk]

On mixing in some speckled stoneware, try a small test maybe; see image just added to my gallery:
On Target! ...buff bloats big time - Browse Member Galleries - Ceramic Arts Daily Community

I'd expected the two buff clays to play nice together.
Not this time, major bloat!
I'd loaded five wares to test; there's enough of that mixed buff greenware to fill the kiln again, and then some...

 

 

[Clay-Tooth]

I love seeing photos! Here are some context shots for the clay I've been working with. Definitely has an overall white appearance that's just softened a bit and with the dimension I really like from the speckles I get from adding Standard 112 to it. It's only about 1/8 of the 112, the rest 617. This photo with the two vases has just a clear glaze over it. Lots of times I leave the clay raw.

[Clay-Tooth]

[Min]

6 hours ago, Clay-Tooth said:

I've been confused about the term grolleg though, and how to determine whether or not a clay has it when it's not in the name or ingredients.

@Min thanks for the recommendation and instructions on using BentoneMA. I was able to track some down online through KY Mudworks.

Now to determine how to best run some tests without filling and mixing up a whole pugger worth of clay (about 25#). I hope to do some tests going forward with some smaller amounts of clay wedging in these fixes the best I can. We'll see if that works...

When you look at the description for claybodies it will say if it's a grolleg body. Price for a grolleg body will be higher than one using a domestic kaolin. Most expensive bodies in North America are the ones using New Zealand haloysite. Grolleg is a blended kaolin clay from England, haloysite is a kaolin like material.  From the blurb about your body:"Grolleg Cone 6 porcelain. This clay body is very plastic and perfict for throwing and handbuilding. Works amazing with glazes and reduces crazing."

Bentone MA is often still called Macaloid, should be readily available from ceramic suppliers.

Nicest reclaimed bodies come from slaking down the scrap into a slurry then drying that out. It's a fairly straightforward way to reclaim scrap. I would suggest doing that rather than trying to wedge in dry mix fix or Bentone MA + water mixture for your testing purposes.

Edited August 26 by Min
clarity