Body color question: om4 and talc containing body

[Retxy]

Hi everyone!

I have found a clay body that I like that I'm mixing myself but that is listed as a white firing body but is actually coming up rather creamy in color. I have learned that the om4 in the recipe can make it fire that way (thanks to digital fire) but to precipitate out the impurities barium carbonate is suggested and im not a fan. Any thoughts on how I can get it to burn pure white? I've got some glazes that are dulled by the creamy color but look so good on whiter bodies and I'm really enjoying the other properties of the body. Mason stains are too expensive so white body stain is not an option. I also considered a different ball clay, but Tennessee 10 for example was too refractory and I think I will lose the vitrificationof the body with a more refractory ball clay. Is there another ball clay that could work?

Recipe is om4, neph sye, talc, and 3269.

Thanks in advance,

Ret

[Babs]

You could coat your ware with a white slip if yoy cant get a white body

[Min]

So you are making a lowfire fritware? Is this a casting body or a throwing body? Have you tried a white firing kaolin instead of the ball clay? How much talc is in the body? If there is a significant amount of talc have you tried firing some to see how white it fires?

[High Bridge Pottery]

13 hours ago, Retxy said:

to precipitate out the impurities barium carbonate is suggested

Barium carbonate will only precipitate out soluble salts not the iron etc. impurities.  I would try every clay you can buy and see which one works the best.

[glazenerd]

Talc has high magnesium, up to 20%: which can alter color. Ball clays need to be under 2.00% total iron and magnesium to keep the color on the white side. C&C ball clay would be a choice. Aluminum content dictates refractory limits. 

Tom

[Retxy]

@glazenerd @High Bridge Pottery @Min @Babs

thank you all so so much for the help!!! its got 15 of talc in in it, the majority is om4. Do any of you recommend any resources (already know about digital fire) that can help with tinkering with clay body formation? I understand some of the ballet of these materials in glazes, but absolutely none of the waltz that is clay body formation. I would love to take the Katz class on this, but am p*ss poor. The recipe I'm using is from an old chappelle book, so I'm not sure about posting it here because I don't want the copyright gods to smite me... but it is a throwing body and im firing it to cone 04 and its vitreous! l

 

I really want to mix my own clay as I live in the middle of nowhere and shipping it out here is often more expensive than the clay itself. I appreciate you all and your kind help!

 

[Min]

It’s okay to post a recipe. 
edit: I asked about recipes and copyright when I started as a mod, was told by admin recipes are considered as a list of materials therefore doesn’t break copyright to post them. 

Edited September 10 by Min

[Callie Beller Diesel]

Just an addition to Min’s comment, as we’ve been having copyright discussions in relation to other things. You can type out the recipe, and you should give proper accreditation, but you shouldn’t post photos of the book page it’s on. 

[neilestrick]

Definitely try C&C. I prefer it over OM4 in terms of feel and workability.

[oldlady]

yes, c&c, definitely, used it for years.  it is white and stays that way.

[Retxy]

Oooh thanks @Min for the copyright info!! @neilestrick To sub c&c in a recipe do I need to juggle the chemistry of the new body in glazy the way I would for a glaze to make them as similar as possible? Is that a good rule of thumb for experimenting with clay body formulas? Thanks!!

D

 

[Min]

Yes, I would. Chem is different between the two, OM4 has about double the KNaO and since you have a vitrified body and the ball clay makes up a significant part of the recipe it probably does make a difference. Other thing is how the clay actually feels, if it gets too sticky sub part of it with a white firing kaolin. It will help the pots dry faster too.

[Retxy]

Thank you so much everyone for your help!!

[Retxy]

On 9/13/2023 at 12:25 PM, Min said:

Yes, I would. Chem is different between the two, OM4 has about double the KNaO and since you have a vitrified body and the ball clay makes up a significant part of the recipe it probably does make a difference. Other thing is how the clay actually feels, if it gets too sticky sub part of it with a white firing kaolin. It will help the pots dry faster too.

Min I will and thank you for this awesome advice. I'm super pumped, feel like knowing you can play with clay body chemistry in glazy is going to make a difference. Can't wait to see what kind of explosions I cause bwahahaha

[Min]

Glaze calc software is for glazes although some functions of it, like oxide amounts can be useful. What is still important is to know the qualities of the materials. Talc for example is good at bringing absorption down if just a few percent are used at midrange but when used at high amounts  it acts as a filler. Also, COE figures are useless as clay is not a glassy matrix.