A weak magnet becomes stronger when it is rubbed with a strong magnet for several minutes. The strong magnet must be rubbed in only one direction. This procedure does not weaken the stronger magnet.
The weak magnet must be placed horizontally on a flat surface while it is being rubbed. Tying a weak magnet together with a powerful magnet also strengthens the weak magnet over a long period of time. The magnets' opposite poles must face each other for this process to work. If like poles are tied together, the magnets repel each other. Both heating and hammering weaken a magnet.