RedArt Terra Sig Question re. Ball Milling and use on Stoneware

[TonyC]

I am trying to make some red terra sig recipes for the first time.   I've read several articles describing the need for ball milling some of the larger grain like RedArt or Newman Red.     I don't have a ball mill nor is one within my personal budget.   Can someone share what they do in this case?   Are there outside services or do you simply make what you can and assume a lower yield due to the larger particles?  

Lastly, can I use these red terra sig recipes on stoneware or are they exclusive to earthenware?  Sorry of this is a dumb question, but I've searched resources and it is not clear to me.

[Kelly in AK]

I’ve made lots of terra sig, from redart and several other clays. I’ve never used, or felt the need for, a ball mill. If I were adding Mason stains I would use one.

You’re keeping only the finest particle size fraction of the clay, accept that you’ll be throwing out the rest. It feels weird at first. Trying to squeeze out “a little more” from the dregs is a false economy. 

Some clays work better than others. Redart and OM4 work great. Lincoln 60 works good. The kaolins I tried were not so great, low yield. The maturing temperature of the clay you make it from affects the fired surface. For example redart will be very hard and satiny at cone 04. Terra sig from OM4 will look a lot the same at 04 as it does green, a little whiter, but also easily scratched, soft. Too many variables to go on about it, just be aware different clays have different properties and making them into terra sig doesn’t radically change those. 

Yes it works on stoneware. The important thing to know is to apply in thin layers, whatever you’re putting it on. It’s not going to be like slip, it needs to be more like 2% milk. Thin. You can build it up with successive coats. Buffing them with a plastic  bag is a nice trick. 

[neilestrick]

I've never ball milled RedArt, either. Milling may increase your finished batch size, but it's not necessary.

[PeterH]

On 7/18/2024 at 1:00 PM, TonyC said:

Lastly, can I use these red terra sig recipes on stoneware or are they exclusive to earthenware?  Sorry of this is a dumb question, but I've searched resources and it is not clear to me.

https://digitalfire.com/article/super-refined terra sigillata
Firing Ranges and Natural Clay Colors Achieved with Terra Sig
A true burnished surface cannot be fired above cone 012. Beyond that, as described earlier, the compressed surface crinkles on a microscopic level, and you loose your shine. On the other hand, highly polished (not burnished) terra sig surfaces can be fired as high as cone 02 with the polish intact. At higher temperatures, terra sigs will give an appealing satin finish, but the high shine will disappear.

I have applied very thin coats of terra sig to bisqueware with adequate results, but it never produces the level of shine or durability of surface achieved with a sig applied to bone dry clay. Terra sig applied too thickly on bisqueware will almost always crack and peel.

At cone 012, Redart sig gives a bright brick-red-orange color. At cone 08 it gives a classic brick red, and cone 02 it gives a red brown. At midrange and highfire temperatures, a Redart (or other earthenware clay) terra sig will fuse and become a glaze.

[Min]

If you add a cadmium inclusion/encapsulated stain don’t ever ball mill it. Stain breaks down and releases the cadmium.

[Callie Beller Diesel]

My college prof worked heavily with Terra sig, and he said not to ball mill any stains, not just inclusions. Lots of them will alter their colour if ground. He said to just add them after ball milling and stir lots. He didn’t believe in using deflocculant, so we ball milled, and even cooked down the results for the shop. 
 

If you want to try ball milling, it’s possible to create your own small version on the cheap that can be mounted on a wheel, but it’s loud and you have to not use the wheel for anything else for a few days. A small rock tumbler might be a better option. But you still discard a bunch of sludge. I don’t know that the yield from ball milling is much more than the kind made by deflocculating and siphoning. 
 

I have used terra sig at cone 10, and can confirm it gets quite pleasantly soft and smooth, but doesn’t have that high powered gloss anymore. If you’re using it at that temp on dishware, I found it wears off outer surfaces with use.