[Why my clay acts like this?]

18 hours ago, glazenerd said:

Hi Tina:

Been following, going through the information you posted. Sand additions are called "temper" in our clay world: first used in native pottery, and later by the brick industry to make clay more suitable for pressing. While sand added to the problem; it is not the problem. You soaked your clay for several days and still had lumps: this indicates the real problem- it is called "cementing." Cementing is a severe form of flocculation; caused by high iron/alumina levels that create a strong positive charge in the clay which makes it resistant to uniform dispersion of particles: which in turn results in delamination, sheering, and cracking. It requires more than adding plasticizers to the clay: you have to break the strong positive charge that creates this problem. Acidity creates flocculation and alkalinity creates deflocculation.

Now lets put that theorem to the test: 1. Find two 1" hard clumps of clay. 2. Fill 2 glasses, bowls, dishes with a 1/2 cup of tap water. 3. Add 1/8 teaspoon of sodum or potassium feldspar to just one  glass (leave the other plain tap water). If you do not have feldpsar; then add 1/8 teaspoon of baking soda.  Stir it well to disperse the powder. 4. Drop one chunk of clay into each glass/bowl. (Do not stir or agitate.) Let it stand for 30 minutes. 5. Use your finger or spoon to see if the clay chunk has dissolved on its own.

If my theorem is correct: then the chunk of clay in the glass with the feldspar/baking soda will have dissolved on its own.  Feldspars/ baking soda create alkalinity; which in turn creates a negative charge in the water; which in turn neutralizes the positive charge that created the "cementing" property.

Tom

This 'cementing' reminds me of the more common 'hard-panning'?

And in other parts of the world temper = grog?

The Canadian Tony Hansen has lots to say about grog but nothing about temper. Glazy doesn't help much either.