Cone 5 Sculpture Clay Body

[bois.hutton]

Can anyone help me convert a clay body recipe from cone 10 to cone 5 without losing the properties that make it a great sculpting clay?  Or, does anyone have a tried and true sculpting clay body recipe that fires fully at cone 5/6?  TIA!

 

I am looking for a cone 5 clay body recipe for sculptural work and tiles.  I have purchased all locally available laguna clays that claim to be suited for these purposes, but they just aren't as good as the clay I'm used to mixing myself -- not enough grog, warp and crack more readily than what I'm accustomed to.  Below are some clay body recipes I've found online.  The 1st is really the one I'd like to use, but I need it to vitrify at cone 5.  Can I convert the Soldate 60 recipe to cone 5?  The VC tile recipe is the right cone, but it doesn't have any fire clay, which leads me to believe it won't be good for sculpting.  I've also found that the best clay for tiles are actually sculpting clays, rather than clays made specifically for tile.  

Soldate 60 (cone 10)

50%  Lincoln Fireclay*
25%  OM4 Ball Clay
25%  60 Mesh Sand
2.5%  Custer Feldspar.

Stephenson Terracotta (C04-2) 

42.3%  Redart
21.5%  Goldart
21.5%  Fire Clay
7.3%  Talc
7.3%  Grog.

VC Floor Tile (cone 6)

5 Wollastonite
6  Ferro Frit 3124
36  Minspar 200 Feldspar
18  OM 4 Ball Clay
20  6 Tile Kaolin
5  Alumina Hydrate
10  Silica
10 Molochite.

 

[glazenerd]

Welcome Bois:

Wish I could answer your questions in a short paragraph: but it will take a few paragraphs to walk you through these recipes. To start: a cone 10 stoneware recipe requires a minimum 10% feldspar addition to achieve any level of vitrification. The Soldate60 recipe calls for 50% Lincoln which is a 60 mesh fireclay: with an addition of 25% 60 mesh sand: which means 75% of this recipe is 60 mesh materials. The OM4 ball clay is the plasticizer and also serves as small particle distribution to help fill the voids that 75% 60 mesh create. The 2.5% Custer (potassium flux) at best serves to fuse the materials together: vitrification will never be achieved at this level regardless. This is a sculptural body- period. You could start experimenting at: 50% Lincoln, 25% OM4, 15% Imco 400 or Gold Art, and 10% Custer. The absorption rate will be dramatically less; but vitrification will not occur. The definition of vitrification being: 3% absorption in stoneware, and 2% or less in porcelain.

The Stephenson Terra Cotta recipe was done on a glaze calculator. Unlike glaze: clay recipe additions of 0.25, 0.50, 0.75% have no real effect on  the outcome. Secondly: Red Art and Gold Art both have higher levels of sulfur (sulfides) than other red clay types such as Imco Burgundy or Newman Red. Red Art produces a good terra cotta color: but firing schedules need to be adjusted to insure you burn out these inorganic sulfides.  Talc is 20% magnesium: which is a low temp melter (1550F range), but it also helps reduce thermal expansion. However, in this case there is not enough of it to produce any tangible results. Low fire bodies are porous: if you can get in the 8-9% absorption range- be happy. This recipe will be low on plasticity: no ball clay additions. 45% Red Art, 15% Gold Art, 15% OM4, 10% Lincoln, 15% talc= 100%, then add 5-10 grog.

VC Tile (cone 6) Cone 6 stoneware typically runs 15% feldspar additions, and cone 6 porcelain around 30% feldspar. The frit and feldspar in  this recipe is 42% of recipe: which means anything besides flat tile would be prone to pyroplastic deformation. The 5% alumina hydrate has been added to offset the effects of high levels of flux. This recipe only has a total of 38% of clay: combined with the other materials puts it in a hybrid category. Kaolin being the primary clay: leaning towards the porcelain arena. Personally, I would be concerned about this recipe fusing to shelfs due to the flux content. A standard cone 6 porcelain recipe is: 50% kaolin, 20% silica, and 30% feldspar; with 2% Bentone MA plasticizer. A common variant is: 35% kaolin, 15% OM$ ball clay, 20% silica, and 30% feldspar. The wollanstonite, alumina, and molochite were all added to offset the effects of 42% flux content. Frit does not to be added to cone 6 bodies: plenty of heat to get the job done. The frit addition comes  from translucent porcelain formulas: not necessary here. 

Tom 

[Min]

That first recipe, Soldate 60 doesn't look like it would be nearly as tight as the Laguna Soldate 60. Don't know what other clay suppliers list the absorption at for their versions of it but I know Laguna's is less than 2% at ^10. May I ask where is that recipe from? What are you looking for as far as claybody colour? Also, does it need to be low porosity at cone 6 or just mature at 6? 

Welcome to the forum.

[Sorcery]

Are you in the west?

In the East I'd try Standard 547.

Sorce

[bois.hutton]

Thank you for all of the input!  I was hoping to find one recipe that would work well as a sculpture body and have <3% absorption at ^6.  Maybe those two qualities are counter to each other, although, the Soldate 60 achieves that for ^10.  I can try the VC Tile recipe and Glazenerd's alteration of the Soldate 60 recipe for sculpture.  

I'm completely flexible on the color of the clay.  It didn't occur to me that you could get low absorption before maturity.  Although, I just found this recipe from Alfred.  It fires to ^10, but at ^6 has 11.35% shrinkage and .62% absorption, which works for me.  

Jr. Tile Red

13  Redart
26.75  Newman Red Sub
10.5  Goldart
10.5  Hawthorn 50M
10.5  OM-4
12.5  Talc
10  Fine Grog
6.75  Medium Grog

The two purchased ^6 clays I've tried for this purpose are Laguna #30 WC601 & Laguna #66 WC610.  These are the only locally available clays to me in Maine that are suited for this purpose.  If I were to order Standard or even other Laguna clays, it would cost a lot in shipping.  I'd like to make my own to avoid paying nearly twice the cost of the clay itself.  Outside of the pandemic, I could probably request a special order for Standard or other Laguna clays, but I don't think my local supplier is offering that right now.

The Soldate 60 I mentioned is from Aardvark: http://www.aardvarkclay.com/proddetail.php?prod=soldate6025lbs&cat=7.  It has .5% absorption at ^10, but I just can't fire that high.  I found it on Beth Cavener's site.  She describes this clay body as having "unparalleled green strength for building large forms, versatility working back and forth between a pliable wet and structural leather hard state, and an ability to withstand high thermal shock. There is a similar product with the same name available from Laguna, but it is missing the key fireclay component that makes it so incredibly strong, plastic, and crack resistant as the Aardvark version."  I'll take her word on the Laguna clay being less forgiving -- I'd like to have the flexibility to make large sculptures.

There's also this recipe from Alfred: Big (Anton's Class) for hand building, ^04-6.  Is it safe to assume this recipe has low absorption since it matures at ^6?  I wouldn't even begin to know how to test for absorption on my own if not.

25  Hawthorn 35
25  OM-4
25  Talc
8.3  Fine Grog
8.3   Medium Grog
8.3   Coarse Grog

[Min]

2 hours ago, bois.hutton said:

The Soldate 60 I mentioned is from Aardvark: http://www.aardvarkclay.com/proddetail.php?prod=soldate6025lbs&cat=7.  It has .5% absorption at ^10, but I just can't fire that high.  I found it on Beth Cavener's site. 

I would hazard a guess that the Aardvark Soldate 60 might have more flux than the Cavener version of it, she fires to cone 2 and notes her version of Soldate 60 easily goes above cone 10. Is it Greenstripe fireclay that you like in the Aardvark Soldate 60?

2 hours ago, bois.hutton said:

Is it safe to assume this recipe has low absorption since it matures at ^6?  I wouldn't even begin to know how to test for absorption on my own if not.

It's very straightforward to test absorption, link here on how to do that and slump testing also. 

 

[glazenerd]

Bois: the recipe from Alfred is more in range to your goals. Given the grog additions; I would use Lincoln 60 mesh in lieu of Hawthorne 35 mesh. I use Hawthorne 35 in one stoneware body: you will find some very course particles- almost cuts the finger. You do highlight one issue: not everyone has ready access to clay.

Tom

[Sorcery]

16 hours ago, bois.hutton said:

low absorption before maturity. 

Though this is true, if they're walking tiles, you may want to realize the full strength of a mature crystal structure.  

For me, underfired has been synonymous with weaker.

Sorce