The raw clay object is dried thoroughly, then fired the first time at a low temperature (around 980°), called a bisque firing, to give a very porous body that looks and feels like a red clay plant pot. The clay is now set and water can no longer affect it, so one can dip it into an aqueous glaze bath or paint on designs with a brush dipped into glaze. I usually rub oxides onto the body and wipe them off with a wet sponge to leave oxides in the texture of the body. After that I usually spray on a transparent or white glaze over the oxides. or dip the body into a glaze bath.
The piece is then fired a second time at a much higher temperature — in my case 1280°C, to melt the glaze and develop oxide colours. Iron oxide give red-brown or celadon green, depending on whether the atmosphere in the kiln is oxidizing or reducing. Copper gives green, cobalt gives blue, etc.
This head was rubbed with manganese oxide to give the brown colour. I applied a transparent glaze over the top part, except near the bottom, where you can see a bit of unglazed stoneware body. The beauty of stoneware is that it vitrifies at the high final temperature, making it waterproof (nonporous), so one can make a vase without any glaze. Porcelain is fired at even higher temperatures, and is also waterproof and beautifully translucent.
Yes, ceramics/firing is quite a slow and difficult process. I learned a lot about it when taking a ceramics class back in the 30s. While I'm no good at ceramics myself, I learned a lot and have a great respect for those that have the skills needed in this department. Even cement must have its challenges. This is amazing no matter what the media though. It's contemporary and intriguing. Really beautiful too.