Substituting EPK for 0M4 in Slip Recipe

[Tiny Island Design]

I have been using a recipe for slip called Pilchers white slip. It has OM4 and an equal amount of EPK, flint, cornwall stone, neph sy with some ziropax and frit 3124. My question is would it be the end of the world if I just used all EPK (since I am out of OM4)? I guess I am going to do it anyway as I am impatient but I would so like to hear what you think. I do know that using EPK in slip that the slip can be somewhat 'eaten' by the glaze but I think that is what the zircopax is there for. Thank you ever so.

[liambesaw]

OM4 is ball clay, so I think the slip would not behave the same.  You can give it a try and see what happens though.  I would guess the things you cast would be very fragile after casting.

[Mark C.]

How about some other ball clays like Kentucky ball clay or Tennessee Ball clay-I have used them interchangeably many times

EPK sub is a bad idea in my view-you need  to clay -a test will be needed

[Min]

I agree, since there's a big chunk of ball clay in the recipe I wouldn't swap it for kaolin. Ball clays are much more plastic than kaolins (in general) so shrinkage will be different with using all kaolin which would likely lead to fit issues. This is a recipe for brushing or dipping onto leatherhard clay isn't it?

Welcome to the forum!

[Bill Kielb]

2 hours ago, Tiny Island Design said:

It has OM4 and an equal amount of EPK, flint, cornwall stone

You may want to look up the clays and pick the next most similar. Testing seems wise regardless of what you do though.

 

[Min]

58 minutes ago, Bill Kielb said:

You may want to look up the clays and pick the next most similar. Testing seems wise regardless of what you do though.

 

Problem with going by the chemistry alone is it doesn't take the working properties of ball clay versus kaolins into account. Easy peasy to get a perfect replacement on paper but the particle size of ball clays are so much smaller than kaolins that it will definitely make a difference to working properties of a slip (or claybody).

Without making this more complicated than it needs to be the simplest thing would be to buy more OM4.

[Tiny Island Design]

Thank you so much. I did hold off, and I do have OM4 on order. Patience. I'm learning. You know what really kept me from making a potential mistake was that I had run out of Talenti ice cream containers! I don't know if you have them in Canada but they are ubiquitous in the US for as containers. I don't even like the icecream that much but thankfully my mom does.