Porcelain stabilized with Epsom Salts

[Selchie]

I am working towards throwing more with porcelain, at cone 6, mostly in oxidation. The closest source of porcelain for me is Pottery Supply House in Ontario (www.psh.ca).  There are two cone 6 porcelains: PSH 910 and PSH 909. When I read the descriptions, #910 says "A bright and white versatile porcelain for use at cone 6-8" and #909 says "Same recipe as 910 stabilized with Epsom salts." I am aware of Epsom salts being used in glazes, but don't know enough about clay, porcelain in particular, to know what the difference would be in the clay by the addition of Epsom salts. Would it be easier (more forgiving) for throwing, or would there be a difference in drying? Or are there other attributes of the clay that would be changed by the addition of Epsom salts?  I will contact a salesperson at the  company for input, but any help would be appreciated so I can be a bit more knowledgeable when I talk with someone at PSH. 

[liambesaw]

Epsom salts are a flocculant, meaning the clay particles will attract each other.  As far as what that will do for you in a clay body...  I'm not sure, maybe it will help porcelain hold together when throwing because it can take more water?   You'll have to let us know what they say

[Min]

Epsom salts will increase the plasticity of alkaline porcelain claybodies. It acts like an acid by changing the way the clay particles align making it easier to work with. It will be less likely to flop and have more strength while throwing than the body without it. If you are throwing I would use the one with epsom salts. The only negatives that I know of are if you are reduction firing with a body containing epsom salts there is more chance of carbon trapping or the odd blister from the body.

 

[Selchie]

Thanks for the ideas. If Epsom salts  will hold the porcelain together and not flop as much, that would be helpful. I will be throwing with it.  Good to know about possibly getting carbon trapping in reduction firing  because I will have access to a reduction kiln, but infrequently.  I will probably stick with stoneware for that kiln.  I can do some testing with less important items in the reduction kiln and stick with oxidation for the pots that are more important. 

 I'll let you know what I find out.

[Mark C.]

Porcelain is just harder to work with no matter what you add to it. Throwing skills are whats needed more than any additive .

[liambesaw]

3 minutes ago, Mark C. said:

Porcelain is just harder to work with no matter what you add to it. Throwing skills are whats needed more than any additive .

I've only used one porcelain known (but not by me) for being bad for throwing.  People describe b-mix as cream cheese, so on that scale, the porcelain I used was more like hot Velveeta.  I'll be trying a different one that's actually for throwing this time.

[Selchie]

My attempts with porcelain have been limited, but good to know that some clays might be somewhat less difficult  than others for throwing.  My throwing is improving, so I'm ready to try porcelain again.  Cream cheese, I think I can handle. Hot Velveeta - can't even imagine! My issues before with porcelain were more with my skill (or lack of it) in drying handles; I think I needed to dry the clay more slowly and carefully than I had. 

[liambesaw]

This stuff was bad, I would weigh out my clay into balls and by the time I brought the balls to the wheel it had slumped into a shape somewhere between sunny side up egg and flan.  So you can imagine what it was like to throw with.  I just made it all into spoon rests and a few small bowls and called it a success.

[Selchie]

Ugh. I think I would have stopped at doorstops (sunny side up egg shaped)  and never have made it to spoon rests and small bowls. 

[Mark C.]

B-mix throws like dream as its white stoneware. The trick to porcelain handles is put them on when the pot and handle are just right and cover them for 1/2 or 1 day under plastic.If you do not put them on jusr right then they will crack. Stoneware is 99% more forgiving in many aspects.

Also porcealin bodies vary greatly in throwing as to legs

The super white ones like Babu or 550 from Laguna Clay throw far worse than say the slightly less white ones like Daves Porcelain that I usew so much of.

I throw small stuff from those grollog bodies as they are like cream cheese.

[liambesaw]

31 minutes ago, Mark C. said:

B-mix throws like dream as its white stoneware. The trick to porcelain handles is put them on when the pot and handle are just right and cover them for 1/2 or 1 day under plastic.If you do not put them on jusr right then they will crack. Stoneware is 99% more forgiving in many aspects.

Also porcealin bodies vary greatly in throwing as to legs

The super white ones like Babu or 550 from Laguna Clay throw far worse than say the slightly less white ones like Daves Porcelain that I usew so much of.

I throw small stuff from those grollog bodies as they are like cream cheese.

Maybe that's what this is. Dove porcelain from SPS, the stuff just does not throw well.  It is supposed to be a translucent cone 6 porcelain and clearly that's asking too much lol.  Gonna try their two other cone 6 porcelains, getting 2 boxes of each, and a white stoneware as well this next time on top of my normal red stoneware order.  Would be nice to have something white in the mix and would love for that to be a porcelain.  WE WILL SEEEEEEE

[Min]

@liambesaw, have you tried Tacoma Clay Art porcelain? The CL192 JG 6 throws pretty well, it's not translucent though and a bit of a grey cream colour. For a translucent body their CL178 NZ6 is really nice and white, throws okay for small and med sized pots, it's translucent when thin. I don't care for Dove porcelain from SPS either. 

[liambesaw]

I haven't tried any of their clays yet, I don't go through Tacoma very often but they're on my list for when I do, thanks for the tip

[Selchie]

Picked up my Pottery Supply House #909 porcelain with Epsom salts today.  According to the potter who works there, there is 2% Epsom salts added to the porcelain. It is designed to counteract the thixotropic properties of nepheline syenite and helps to make the porcelain more plastic.  The salesperson uses #910, but she is a much better/more experienced potter than I am.   She also suggested using wax,  at the leather hard stage, around the connections between the handle and the body of the mug, to prevent cracking. I'll give that a try - and open to any other suggestions on that score, as well. 

Thanks for all of your input!

[liambesaw]

6 minutes ago, Selchie said:

Picked up my Pottery Supply House #909 porcelain with Epsom salts today.  According to the potter who works there, there is 2% Epsom salts added to the porcelain. It is designed to counteract the thixotropic properties of nepheline syenite and helps to make the porcelain more plastic.  The salesperson uses #910, but she is a much better/more experienced potter than I am.   She also suggested using wax,  at the leather hard stage, around the connections between the handle and the body of the mug, to prevent cracking. I'll give that a try - and open to any other suggestions on that score, as well. 

Thanks for all of your input!

Even with porcelain I have found that I never get cracks if I attach at leather soft and put it in a wet box to equalize.  A lot simpler than waxing all the joints

[Selchie]

Thanks for the suggestion! Using a wet box would make me much happier than having to use wax resist. 

[neilestrick]

Waxing joints doesn't help IMO. The problem is that the entire handle is shrinking, not just the joint. Because the handle is wetter than the pot, it shrinks more, and cracks develop.

[neilestrick]

Standard 365 cone 6 grolleg porcelain throws really well, and is white and translucent. I've used it for years. I've even used it for 4 piece, 50 pound planters with no cracks or warping. If there's a Standard distributor out there, give it a try.

[Selchie]

Thanks. I will see if I can find the Standard 365 porcelain. Will try throwing what I have, too, because if it works, I get it right from PSH. 

I agree about the wax not working, unless I do the whole handle, I can't see how it would work, the more I think about it. I don't want to spend all sorts of time putting wax on handles, if I don't have to do so. I had one handle crack right in the middle. Really frustrating after working with stoneware. I will try putting them in a wet box and see if that will help. 

[Bill Kielb]

33 minutes ago, Selchie said:

Thanks. I will see if I can find the Standard 365 porcelain. Will try throwing what I have, too, because if it works, I get it right from PSH. 

I agree about the wax not working, unless I do the whole handle, I can't see how it would work, the more I think about it. I don't want to spend all sorts of time putting wax on handles, if I don't have to do so. I had one handle crack right in the middle. Really frustrating after working with stoneware. I will try putting them in a wet box and see if that will help. 

To all these stories, when I first started throwing I bought 50 pounds of stoneware that was so wet it was near Jello. I practiced so much with that, thinking when will I ever learn to throw taller than 6” vessels.

Turns out it was great practice as now I throw most porcelains anyway I like  and it seams easy. Standard 365 is easy and cone 6, 267 same but cone 9 I believe. I throw Laguna Frost right now because it’s really white and translucent even at 1/4”.

It makes  for great carved votives (translucency) and really white bowl interiors with clear glaze. Don’t like Bmix anymore - too messy for me now. 

[MFP]

I am not having trouble throwing any of the porcelains I have tried so far......but cracking....that's another matter. I compress and compress and compress, make sure the bottom and the wall are the same thickness, cover everything and it still cracks.  The only thing I can think of is that it gets hot as hell in that shop and even with plastic something is happening....maybe they are sweating  when it is hot and then reabsorbing the moisture at night when it cools down and then pulling apart?  I can't figure it out.  It's even cracking on the bat when the pot is turned. ( Got my B mix==trying that next)

[Bill Kielb]

@MFP

Bmix is pretty forgiving so if it cracks then I would say change up your drying method. Even my toughest porcelain (Laguna Frost) drys fairly quickly without cracking if my throwing techniques are good.  I usually throw the mug on the wheel head, cut it off and set it on a cheap Cfold towel often on a wood bat or ware board. From there I use a technique Jennifer McCurdy showed me where the plastic is gathered, inserted in the center of the mug and just allowed to drape over the sides all around. The cfold towel (paper towel) wicks water away from the bottom nicely and the loose plastic allows it to dry leather hard in a day or so.

 Most of my cracks used to be at the bottom so we found a way to make sure the bottom is very compressed. Has worked for our students pretty well for some time as well.

here is a quick video of what we do that has eliminated many of the cracks in the bottom.

 

[MFP]

Thanks Bill! That was most instructive. I am not having problems on smaller things....it is the 8-12 inch things that are giving me trouble,.....none of the lids crack which are unpide down shallow bowls....so I am doing something right with them. I never thought of spreading the porcelain clay out like that instead of opening it.....and the out to in compression makes a lot of sense. I will definitely try it as the compression  technique I was taught in the past is not working and is exactly the opposite. I used to make whole dinner sets without any problems. So this has been a bit mystifying.  Also the clays have varied from being relatively soft to being quite stiff.  

[MFP]

Went out and practiced this today. I did note a difference in how the center felt. We will see if it cracks.