Top picture is the head after the last pour. I found that using alginate on bare clay causes lifting of the clay, and can damage fine edges. Two very thin coats of lacquer fixed that.

After inumerable tests, I finally figured out how to get rid of the fucking bubbles. And yes, that's what type of bubbles they are. I tried a thinner mixture, more mixing, pouring water into the alginate and vise versa, but nothing made any difference. Then I noticed that when I peeled the alginate out of the mixing containers, the undersides were smooth. So, I epoxied a piece of wood onto the clay bust (see second from top photo) and put the sucker in upside down. After pouring in the alginate, I heaved the head up and down like a plunger for a good while.

And it worked! Finally. I can get on to the next step, making a rubber mask out of liquid latex from the alginate.