Bricks have been traditionally used in this practical and they work very well but newer bricks tend to be harder in construction and so do not break up easily. The best bricks tend to be 'London' or 'stock' bricks which are softer solid red types with a 'frog' (square indentation). Harder engineering bricks which usually have holes through them are too tough to be broken up successfully in this practical.
Small plastic pots need to be found for this practical. They need to have necks big enough to insert pieces of brick or chalk and must have a tight fitting screw cap. Old cosmetics pots work well.
Students take freshly broken up pieces of brick or chalk which have rough edges and place them in a pot. The lid is screwed on and they are shaken vigorously for a couple of minutes. The shaking simulates erosion that takes place in streams and rivers where rocks crash into each other, breaking them up into smaller pieces and creating smooth surfaces.
After the practical, the smoothed chalk pieces may be kept for other uses. The pots should be cleaned of any debris and reset with new pieces so they are ready for their next outing.