Ah, so you wish for me to divulge the ancient alchemical process to you? Very well. I shall share this esoteric knowledge.

So, here's what you do.

Step One: Boil some rice. Ideally without salt. Boil the crap out of it, until the water turns white. You don't need a lot of rice. Half a cup is plenty for making a pot. Then, strain the rice, and KEEP THE WATER.

Step Two: Boil down the rice water. How much? Until it's nice and good. You'll figure it out. Just don't burn it. Once it's thicker than regular water, you're good.

Step Three: Get a haricut. Not for aesthetic reasons. You will need hair for this process. How much hair? I think you already knwo. Enough to be enough. Chop it up real fine. Around one to two milimeters in length.

Step Four: Get some vinegar. You'll need it for this recipe. It slightly helps with plasticity, and prevents the clay (which will have rice water in it) from growing mold while it dries (probably).

Step Five: Grind your refined clay into a fine powder. You can use a mortar and pestle that you have previously crafted out of clay. IF you don't have one, just use whatever to get the clay at least as fine as aquarium sand. It's gotta be easy to mix.

Step Six: You just kind of mix all those things together. Start with the dry ingredients of clay and hair, mix them good. Then add the rice water and vinegar to hydrate the clay powder.

In the end, the clay will be much more plastic and hold together easier until it is fired. Although this process is mostly for upgrading lower quality clay. You should focus on repeatedly refining your clay by decanting. You first get rid of silt, sand and any debree, and once you got what is mostly clay, you refine that the same way. The finer the clay particles, the better the clay, so you will lose A LOT of clay during the repeated refining process if you are starting with a low quality source.

If you did al-Razi's method correctly, your finished piece should be hairy like a kiwi fruit once it is dried (but before it is fired, all the hair and other non-ceramic stuffs burn away during firing).

Edit: IMPORTANT!!! Once you make your alchemist clay, use it right away. It WILL start to rot and mold if you leave it wet for too long. It has rice water in it, of course it will rot. DO NOT make my mistake and leave it in a bucket covered in foil. That's how you get a funky fungus that ruins your entire batch.