Tumbled bricks are just regular bricks that an antique dealer would describe as "distressed." They have rounded edges and enough nicks, dings and scratches that they look as if they've been around forever and had a hard life. This can be done artificially by tumbling to mimic the look of old, reused or even handmade brick.
To make handmade bricks, fill the moulds by hand with wet clay or mud. No mould is ever hand-filled quite the same way or quite perfectly, and when the bricks have dried and you remove them from their moulds, no two are exactly alike. Handmade bricks also tend to have rounded edges. This method is the classic way of making adobe bricks in the Southwest desert.
Extruded bricks are formed in a machine by pushing wet clay through a specifically sized opening so that it comes out in long ribbons, which are then sliced into uniform lengths. Extruded bricks have sharp, clean edges and are all exactly the same size.
Tumbled Green Brick
Green bricks are unfired, meaning they have been air-dried but not heated in a kiln to harden them. You can put green bricks into a tumbling machine. This machine looks like a barrel and has bars and knobs on the inside. It turns on its long axis. As it turns, the bricks roll around and bang against each other and the walls of the machine; this deforms their edges and make dents and marks on their surfaces to make them look old and weathered. Because they have not been fire-hardened, some of them will shatter during tumbling.
Tumbled Fired Brick
You can tumble fired bricks to chip the edges, which helps make them look used. They will deform and "age" less than green bricks because the fired bricks have already been kiln-dried at high temperatures. Fired bricks are also less likely to shatter than green bricks. Place all extruded bricks to be tumbled in a tumbler by hand, which makes them labour-intensive and adds to their cost.