Brick with Black Holes - Pop Quiz

How is it these bricks have black holes?

Check out the original mortar with its flecks of quartz and feldspar. It's almost 100 years old and remains perfect.


ty.ro said...

Sometimes certain minerals were found in specific clay bodies. During firing these minerals burned out (causing some interesting glazing techniques; in this case black spots).

Check out natural glazing techniques for clay, its really fascinating. A lot of it has to do with salts/minerals in the clay. Even certain glazing techniques are done by throwing a shovel full of salt into a hot kiln, having beautiful results.

Christian said...

Hi ty.ro!
Sorry for the late response, you wouldn't believe the series of distractions.
You're the winner of course.

I believe flecks of iron ore were used in the brick in this photo.