Jump to content
Sign in to follow this  
harleyweigle

Clay Plasticity Wrong?

Recommended Posts

Hey Everyone! 

 

This is the first time that I have been on here and I am extremely looking forward to being a part of this amazing online community!

 

Buuut most importantly I have a clay question for all of our leading clay experts and home clay mixers out there.

 

For about three years now I have been mixing a cone 10 stoneware body of clay for a college university (I am an undergraduate ceramics major and studio assistant here.) and over the three years time doing so I've notice that the clay doesn't really have any plasticity to it. When I throw with this body it seems and feels porous. It doesn't stretch well and certainly doesn't throw for good bowls. Lastly, I can not use it for handles on attachments. When I pull and then shape the handles it simply cracks where the curve of the handle begins. When I make the clay I typically allow it to sit for about two weeks before I use it but this does not seem to solve the problem either. The formula I use to make the body is as follows:

 

Hawthorn Bonding- 5 Parts

Foundry Hill- 5 Parts

Red Art- 1 Part

Ball Clay- 2 Parts

Feldspar- 1 Part

Fine Grog- 1.5 Parts

 

If anyone could give me any tips on how I could achieve a greater plasticity like the Cone 10 Stoneware that you can buy from clay suppliers that would be extremely helpful!

 

Thanks Again,

Harley

Share this post


Link to post
Share on other sites

The standard answers are. A. Bentonite. B.wet mix (blunge mix) clay then dry to consistiency. C. Age it....

 

I cannot comment on regarding recipe I've never tested ingredients.

 

Some swear that moldy clay is more plastic. i like get a clay moldy especially porcelain. . I keep a few rags around and "inoculate" other clay.

 

But even without aging I've been able to get poreclaineous clays to be quite plastic.

 

In college setting often there is no room or time to age clay in large quantities. I'd consider adding a plasticizer. There are other higher tech a plasticizers like vee gum t, And a secret one I've been working wiith. I'm pretty sure some mist if not all of the major clay mfgrs. Are using more than bentonite

 

Another solution is go with a recipe that is known to be plastic, if your not committed to this recipe. What is history of your recipe?

Any chance you are mixing your clay too dry?

 

I haven't worked with foundry hill. Also what is your absorption % at cone 10? Thinking you might be a bit low on flux. Also look into theory of mixing particle sizes of grog . 48f has a range of particle sizes. While not a plasticity solution, may improve body.

 

Without more info and simplest answer is. Test with 3% bentonite addition. (I prefer to blunge bentonite a day or 2 before. )

Share this post


Link to post
Share on other sites

Wow, that recipe's not plastic???

How wet are you mixing it? (If the particles aren't thoroughly wetted, the batch could indeed be quite short)

Do you add vinegar, yogurt or a few pounds of reclaim to the batch?(this can help age things more quickly)

6 weeks aging might work better, too.

 

Do you notice any improvement in the throwing properties of, say the trimmings reclaimed from slurry?

 

With both the ball clay and the red art, I wouldn't *think* bentonite would be necessary, but.. (Shrug)

Share this post


Link to post
Share on other sites

If you're not pugging it, which I'm guessing you're not since that should be a plenty plastic body, no amount of added bentonite or other plasticizer is going to help. You either need to pug it, age it longer, or mix it as a slurry and let it dry to a workable consistency. What you're experiencing is what we call 'short' clay. The clay particles aren't adequately wetted, meaning there's a lot of air in the mix, which prevents the particles from sticking together well, hence the cracking and 'porous' feeling. There's a lack of density. Ideally, each clay particle is coated with water, without air spaces between. Mixing it as a slurry achieves this well, but probably isn't a practical method of mixing large amounts at your school. A de-airing pug mill pulls all the air out of the clay and gives you a nice dense mix, which is how most people make clay. First the mixer, then the pugger. Aging the clay has the same effect as pugging, but takes a lot longer. Two weeks probably isn't adequate to make a big difference in the workability of the clay. I would give it a few months.

Share this post


Link to post
Share on other sites

Neil:

 

Our pug mill has been broken for the past year so I have not been able to pug the clay after I have mixed it.I am extremely grateful for the solution that you have provided and will try both aging longer and mixing at a wetter consistency and then drying to a workable state. With that being said I have another question. 

 

Is there any benefits to one over the other. Does allowing a slurry to dry to a workable consistency yield a better clay body than mixing a workable body and then running it through a de-airing pug mill? Assuming both ways allow the same amount of time for the aging process?

 

Harley

Share this post


Link to post
Share on other sites

I think slurry mixing is king. It saturates, if you will, the particles. A pug mill mixes and to an extent " compresses" possibly increasing saturation... de airing as little to,do with plasticity In my book, I dint feel any difference with mixed clay and de aired clay after wedging both. I only had the opportunity to use de airing pug mill a few times. I'm told the best clays are slurry mixed then filter pressed.

 

When I first made my own clay body, I used a pair stirrer on a drill to make slurry, Then into pillow cases, which were held by fancy root maker growing pot. The porcelaineous body was so plastic I lowered the bentonite %. You can make a pretty effevtive and larger scale system easily with hardware cloth 2x4s and an old sheet. Im still using latter system, Even though my pug mill can mix and pug.

 

What kind of mixer are you using? How large a batch do you make? And how often?

Share this post


Link to post
Share on other sites

Biglou,

 

Awesome! Thank you very much it makes since that would be best. I am curious to know since I have just purchased a mixer and small bluebird pug mill and will soon start these studio practices for myself and my own business.

 

Thanks,

 

Harley

Share this post


Link to post
Share on other sites

Nerd: "short" clay (as opposed to plastic clay) describes clay that acts much like short pastry crust: crumbly and doesn't stick together or stretch very well. I've noticed a lot of potters think with their stomachs. You'll sometimes hear people refer to leather hard as "cheese hard" as well.

 

Harley: I've used both pugged and slurry mixed clay, and I will say that slurry mixed is indeed preferable, but it is also a LOT more labour. Pugged clay isn't bad at all if you can mix a few batches before the semester ends and let it sit over the summer. At that point, it will have comparable plasticity to a slurry mixed clay. Your back will thank you, especially if you're making clay for a college.

Share this post


Link to post
Share on other sites

Clay that is pugged and de-aired doesn't really need aging. The pug mill pulls out the air, drawing the water around the clay particles through capillary action, resulting in good wetting of the particles. I can definitely tell the difference between clay that has been de-aired and clay that has not been de-aired. I think many small studio size pug mills do not work as well as they should, mostly due to improper maintenance resulting in clogged vacuum lines. But with industrial pug mills, like those used by clay companies, there is a noticeable difference in the look of the clay when it is cut into blocks if the vacuum was not working properly. Slurry mixing is probably best, but a much slower process.

Share this post


Link to post
Share on other sites

neil would you consider

 

http://www.peterpugger.com/pugmill-extruder/pm-60-pugmill.html

 

a studio sized pug mill?

 

i suspect improperly maintained.....

 

I love Peter Puggers! You mix a batch, suck out the air, then extrude it. You can see very easily if the vacuum is doing its job. I've just seen a lot of standard puggers that have clogged up vacuum lines. People get to pugging several hundred pounds, shoving in a couple pounds at a time over a few hours, and they don't check to make sure it's working properly.

Share this post


Link to post
Share on other sites

Big Lou I have the VPM-30-I got a deal on it used and its been a power house mixer.Never had a vacuum issue in the last two years I have used this machine-the 30 is perfect size for me.

The barrel is aluminum and will pit over time with porcelain which is all I use it for. It holds 85# and will process about 65-75# as the rest is always in machine. The VPM 60 is a huge machine  in terms of output, which would work for schools or major users like ceramic art centers. 

Share this post


Link to post
Share on other sites

bailey makes a good pugmill.  mine is one of the smaller ones and nearly the first one offered.  it works very well, producing clay that looks and works just like the stuff out of the box.  i can slice the pugs in any direction and not find any air bubbles.  putting wet and dry pieces into the hopper blends the clay to the consistency i want.  their website has a video of blending two colors of clay.  it really does work that well.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.