Types of porcelain cone 9-10 (oxydation)

[Danielle Caron]

Hello,

I am just starting to experiment with cone 9-10 porcelains (oxidation). Purchased PSH 900 and PSH 905 as suggested by the ceramic shop here in Montreal - the only brand they said they had - and their 905 is so hard, almost starting to dry. It obviously has been sitting on their shelves for a very long time.

So I am asking for your input , since I cannot purchase  just 1-2 boxes of other brands for tests due to, of course, shipping issues for such small quantities, and it would have to be a product that can be bought in Canada.

I was told not to start with the cone 10 transparent porcelains, since they are more difficult to work with (planning to do so at a later time). I am used to work with cone 6 Tucker's Bright White. It doesn't have to be a transluscent porcelain, but I surely would like to work with a very white one.

Do any of you have a preferred brand that you have been working with? Particular characteristics? I am looking at the following options: Plainsman Polar Ice, P-700, P-600 or Tuckers' H.H.P. or 10-80. It will have to be a wild guess after that.

Thanks in advance.

D

 

[neilestrick]

First, if you're firing in oxidation, there's not a lot of good reasons to fire to cone 6. Just about anything you can do at cone 10 oxidation you can do at cone 6 oxidation, and your firing costs will be lower and your kiln will last longer. This is especially true if you're firing in an electric kiln. Cone 10 will just burn out your elements faster and wear out the kiln faster.

There are a lot of good cone 6 porcelains out there. The translucent bodies are typically grolleg porcelains, and they may or may not be more difficult to work with than domestic porcelains. Grolleg bodies are the whitest, so I would go ahead and jump into a couple and try them out. 

[Danielle Caron]

Thanks. The thing is I want to try a couple of very specific oil spot glazes that are fired at cone 9-10 with porcelain as a clay body.  

ConeArt tells me that their kiln (my kiln) is really ok to work with at cone 10, given that the elements might wear out faster. I wouldn't want to wear down my kiln in a year because of high fire, though. 

 

[neilestrick]

58 minutes ago, Danielle Caron said:

Thanks. The thing is I want to try a couple of very specific oil spot glazes that are fired at cone 9-10 with porcelain as a clay body.  

ConeArt tells me that their kiln (my kiln) is really ok to work with at cone 10, given that the elements might wear out faster. I wouldn't want to wear down my kiln in a year because of high fire, though. 

 

Yes, it will definitely fire to cone 10 just fine. If you only do cone 10 and bisque rather than cone 6 and bisque, it will cut your element life by 50-60%, and the bricks will wear out a lot faster. But the occasional cone 10 firing for a special glaze isn't going to hurt anything. Just make sure you're keeping your cone 6 and cone 10 bodies separate so they don't get into the wrong firing. A cone 6 body at cone 10 will slump, a cone 10 body at cone 6 will be under-fired and may weep.

Go with a grolleg porcelain.

[Min]

7 hours ago, Danielle Caron said:

I am looking at the following options: Plainsman Polar Ice, P-700, P-600 or Tuckers' H.H.P. or 10-80.

Plainsman Polar Ice is technically a cone 6 clay. I know on the info page for it there is mention of it going to cone 8 in an electric kiln and cone 10 in reduction but I'm thinking there is going to be more warpage and slumping. I use a bit of Polar Ice, it's ridiculously expensive plus it takes some work to get it into a good throwing consistency. You need to wedge it on plaster or dry it out before throwing with it. It seems rock hard when you open the bag but once you start wedging it it goes very soft. Plainsman P600 (epk body) is okay but it's not as white as the P700 (grolleg body). 

If your ceramic supply place in Quebec is bringing in PSH clay then I would also look into the Laguna bodies that PSH offers. It looks like they can bring in ^10 Frost which uses New Zealand halloysite instead of EPK or grolleg, same as the Polar Ice uses. It's very white but I know some people find it a bit of a pain to throw. Halloysite bodies are super white but they are definitely more costly than grolleg bodies in Canada. If any of the Laguna bodies look any good then see if your supplier will bring in a box or two for you with their next order. Saves you ordering from the U.S. and dealing with shipping etc.

 

[Mark C.]

One note on some of the glassy porcelains and that is you cannot recycle them with other white clays. So just keep them separate .

[Callie Beller Diesel]

Plainsman makes some most excellent stoneware clays, but isn’t known for it’s porcelain. They’re working primarily with clays from the geologic deposits in Southern Alberta and Saskatchewan, so there’s a lot of secondary clay. With the exception of the Polar Ice, the Plainsman porcelains will not be super brilliant, glassy white porcelains. They do fire quite white, but neither P600 or P700 have anything resembling a glassy quality to them. On the plus side, they are also less fussy than other porcelains. I’ve seen the samples in person and worked a little with them both: the pictures that compare p600 and p700 to Coleman porcelain  on this web page are quite accurate.

The Polar Ice has been described to me by a few friends that have worked with it as a very high maintenance item. But when fired at cone 6, it looks as glassy as Corelle. It’s VERY translucent.

[Babs]

Folk get great oilspIt glapzes at cone 6 ,just saying, research John Britt midfire oil spot glazes. Also on Glazy. Much more economical.

[Min]

11 hours ago, Babs said:

Folk get great oilspIt glapzes at cone 6 ,just saying, research John Britt midfire oil spot glazes. Also on Glazy. Much more economical.

There are some oil spot cone 6 glazes but IMHO they don't have the depth and visual complexity of high fire ones. For high fire oil spot glazes the Fe2O3 red iron oxide in the glaze recipe has to get to around 2250F at which point it lets go of an oxygen atom and breaks down to FeO black iron oxide. The released oxygen molecule moves through the glaze along with some of the iron. When this iron gets to the surface of the glaze it leaves the "oil spot" iron deposit. Fire an oil spot higher and the iron will start to flow in the now more fluid glaze and give you a hare's fur or partridge feather glaze. The other type of "oil spot" that can be achieved at lower temperatures would be a boil through glaze, I haven't seen one of these that looks like a high fire oil spot. 

 

[Babs]

3 hours ago, Min said:

There are some oil spot cone 6 glazes but IMHO they don't have the depth and visual complexity of high fire ones. For high fire oil spot glazes the Fe2O3 red iron oxide in the glaze recipe has to get to around 2250F at which point it lets go of an oxygen atom and breaks down to FeO black iron oxide. The released oxygen molecule moves through the glaze along with some of the iron. When this iron gets to the surface of the glaze it leaves the "oil spot" iron deposit. Fire an oil spot higher and the iron will start to flow in the now more fluid glaze and give you a hare's fur or partridge feather glaze. The other type of "oil spot" that can be achieved at lower temperatures would be a boil through glaze, I haven't seen one of these that looks like a high fire oil spot. 

 

I agree , I offered that as an alternative. If the clay sought is for one glaze, it is not a step I'd be taking , septuagenarian here though, just know 2 similar looking clay bodies, different firing temps, win one pottery shed can be a bummer. But that is me

[Danielle Caron]

Was already in the process of  trying a few oil spot recipes at cone 6, but I need to see the difference between cone 6 and cone 10 to make a well informed decision. Thanks to all for your input, all the infos on the different types of clays, firing process of oil spot at cone 10 and firing impact on my kiln.
All this is going to be very helpful.

[Danielle Caron]

23 hours ago, Min said:

There are some oil spot cone 6 glazes but IMHO they don't have the depth and visual complexity of high fire ones. For high fire oil spot glazes the Fe2O3 red iron oxide in the glaze recipe has to get to around 2250F at which point it lets go of an oxygen atom and breaks down to FeO black iron oxide. The released oxygen molecule moves through the glaze along with some of the iron. When this iron gets to the surface of the glaze it leaves the "oil spot" iron deposit. Fire an oil spot higher and the iron will start to flow in the now more fluid glaze and give you a hare's fur or partridge feather glaze. The other type of "oil spot" that can be achieved at lower temperatures would be a boil through glaze, I haven't seen one of these that looks like a high fire oil spot. 

 

Given that, would you put a hold at the maximum temperature, or just slower cooling down (I have several firing schedule options with slow cooling so far)?

[Min]

Given that oil spot glazes are stiff glazes that need to go on thickly to get the oil spotting plus not knowing how slowly your kiln fires towards the peak temperature/cone I can't really answer that. The glaze is going to need time to smooth over so it's a balance. Soak it too long and the spots will run, don't soak or fire quickly and the glaze might not have time to heal over.  I'ld try with a soak first and see how tests come out then go from there, if you get more of a hares fur then reduce the soak time. (put waster cookies under your test pieces plus I would make the test pieces fairly large to get  more accurate results)

[Babs]

Is the oilspot you are seeking fired in reduction or oxidation?

The ones I drool over are ones fired in reduction.