Talc In Low Fire Clay?

[Dennis Bednarek]

As an individual that is fairly new to ceramics To date I have only used three different low fire clays.  Two different terra cotta clays and one white high Talc clay.  I had noticed a considerable difference between these clays.  In working with them I noticed the white clay drys extremely faster than the others. The green wear of the white clay also is much more fragile than the Tera Cotta I initially used.  I also prefer it considerably wetter in order to work it the way I prefer.   And finaly during firing I had experienced my first blow outs with the white clay..

Considering this is a high talc clay without grog could the talc be a factor making this clay so different than the terra cotta clays I have been working with?  Is there a white Clay that mimics the Terra 
Cotta more.  My thoughts were trying to find a white clay woithout Talc and possibly with grog to be get closer to the terra cotta as far as workability.  I prefer the white color but for workability I'm in favor of the terra cotta clays now.

 

Any advice would be appreciated.

[glazenerd]

Hi Dennis:

 

Talc is not soluble in water and is classified as a being hydrophobic ( which means it repels water). That explains why it dries so much faster than your other clays. It is also relatively high in magnesium: which in this case gives it a fluxing property of its own. This might in part explain problems when firing it to the same temps as you other clays. It does have low tensile strength green, but forms a rather hard surface after firing. Others could address this further than I; but I think the simple solution is to cover your pieces with plastic to impede the drying process. You stated you preferred to work with wetter clays: int the case of a talc body it will repel most of it anyway. I do not do low fire, nor do I work with low fire clays: so I will let those who work in this range make suggestions for clays.

Nerd

[bciskepottery]

Standard Clay makes a white, low-fire clay body with talc or without talc, with grog or without grog. I believe some schools prohibit talc in clay bodies.

 

http://standardceramic.com/products/moist-clays/low-fire-clays/

 

White low-fire is not earthenware; it is a manufactured low firing clay body. Talc makes the clay gray in the wet/unfired stage. Earthenware/terra cotta is a true earthenware with iron. You can get either with or without grog (smooth or not smooth). Each has their own characteristics, including the level of fragility in the green state. I've use a groggy red sculpture clay body where I could literally attach pieces at greenware stage with some spit and they would hold fine. Using that with other clay bodies is a disaster in the making.

 

Best option is to try a groggy non-talc white low fire. If your dealer does not keep them is stock, they can always order them for you. You can also get grog from the clay store and wedge it into your smooth talc low-fire.

[terrim8]

You could try mixing your own talc-ball clay body. I make a 50/50 by weight clay body and use it for my pit fired pottery. It bisques to a nice white colour and works good with terrasig. It might be a fun experiment for you to try- just mix with water, dry on plaster,  then wedge  and age it in plastic for awhile- maybe a month. It will still be quite moist after a month. 

[neilestrick]

The main reason the red and white bodies behave so differently is their clay content. Terra cotta bodies are usually 85-90% red clay plus 10-15% ball clay, and sometimes a little grog, so almost entirely clay. Low fire white bodies are only about 50% clay. So their workability and drying times are totally different. It's just their nature. You're probably not going to find a low fire white that feels like a terra cotta.