Which Potash/feldspar?

[Estelle]

I'm trying to understand Feldspars / Potash and Spodumene to strengthen a homemade paperclay body from thermal shock.

 

Is Potash that I use for gardening and enriching tomato plants the same stuff as POTASH FELDSPAR?

 

Are all Feldspars alike? Does feldspar simply mean potash in ROCK FORM?

 

Does homemade (burnt wood/plants to ashes) POTASH have the same qualities as Potash Feldspar or gardening Potash?

 

I bought some SPODUMENE to add to my clay body to prevent cracking because

I will be firing my sculptures with a fire pit of wood and coals. So far all my paperclay pieces

have sadly cracked instantly during firing in a metal container.

 

Would Potash (for gardening) do the same thing - prevent thermal shock and strengthen the clay body?

 

Is POTASH (for gardening) actually a Feldspar?

 

Thanks, any advice most welcome!

[MMB]

So youre putting greenware into a fire pit? Theyre not bisqued before hand? If so then the reason theyre cracking instantaneously is more than likely due to too hot too quick. Too much heat to quick can crack even ware that has been already bisque fired. But really though if youre firing that way it is an extremely hard process on clay. I pit fire and its hard enough on bisqued items, so green ware has an even harder time. Also to if youre sticking to this metal bin firing then you are getting no where near the temp needed for feldspars to be affected, last time I checked they done start to melt till ^4 so i doubt theyre helping fuse in a 900 degree fire. As for the gardening question Im not sure.

 

I dont have solid evidence but I did read recently that Mica gives the added benefit of provided good thermal shock properties.

[Estelle]

Thanks for sharing your experience with pitfiring, I watched videos of classes using Shichirin's to fire their tea cups after drying with a hairdryer first. Some cracked others didn't. The artist says Shichirin's can reach over 1000 deg C.

 

I've studied a basic ceramics course, but we used electric kilns which the students had to concentrate on potting and didn't have to attend to the firing science, as the teachers did it all for us. So all my firing is pretty experimental at the moment.

 

Thanks for the using Mica tip, shall check it out. I was informed by a clay stove designer that spodumene was the secret ingredient for thermal shock.

 

My main concern is what is can potash made from ashes, or potash for garden match the qualities of spodumene (lithium feldspar)?

[Tom]

Potash that is used in gardening is not a feldspar. Potash feldspar is a naturally accruing compound that has a Potash salt in it. If you need a potash feldspar get it from a ceramic supplier. I don't know of any other places for that product, although there may be some. If you want to experiment the gardening potash try it in glazes test and clay test. It should be a fluxing agent and may turn your clay to glass. That might give you a new glaze base to perfect. It might give a mess in your kiln. Use sagers to test it.

 

There are several types of feldspar all are fluxing agents, a have different properties. They all flux at different temperatures. Feldspar is most likely not the product you would look for if you are trying to fight thermal shock. For that you would want a filler like Silica, Spodumene, Grog, among others.

 

by the way, Spodumene is an element of pyrex glass ware. It used to reduce thermal shock in the glass.

 

Hope this helped

 

Tom

[Estelle]

Thanks Tom, for this specific details on feldspar.

This is so helpful!

I got the idea of using potash (from burnt wood) from the

s

glazes on this ytube video. So I next experiment with making a potash glaze using my

garden mix. Unfortunately I do not have access to a kiln, but will try a saggar fire in my shichirin.

The picture below is the metal flower pot bucket I used to fire my recent cups.