Almost daily, I get an email about making masa for tortillas. The difference between masa and cornmeal (or polenta for that matter) is that the corn is processed with a procedure called nixtamalization. Dried, starchy corn is cooked and the soaked in limey water. Later the corn is rinsed and rubbed so that the indigestible, clear skins are removed.
Calcium Oxide, more commonly known as Cal, is used in Mexico. I've always seen it powdered and ready to use but this last trip I found it in rock form and was told it was much better like this. I'm not sure why other than maybe it's not as processed.
American Indians use wood ash and I've heard that Southerners use lye when making their hominy grits. I've only experimented with the Cal. You mix a bit with some water (and at this point you have Calcium Hydroxide) and add it to the corn and water. The corn becomes a beautiful, lurid shade of yellow and you know that things are working.
The smell of the cal, water and corn is indescribable and unique. It fills the kitchen and is a fine clue that good things are coming.