Under the transparent foil, there are microscopic iron filings floating in a special solution. Moved by the magnetic force of a magnet, the filings attach to the foil. The magnet in the shape of a strip on the other side of the board is used for erasing your doodles.
The screen of the board is divided into hexagonal cells to avoid drawing all the solution in one place. The paraffin oil is the solvent here, and the magnetic material consists of iron file dust or, better, iron oxide. The iron oxide, the magnetic material of the first Chinese compasses (which was discovered in Europe by sailors from the Italian town of Amalia) is called magnetite.
The magnetic sketcher is a newer version of the old game of drawing moustache on the grandmother's picture. In that game the iron filings were a little bigger. And the pen was a little magnet. Be careful not to make a hole in the foil when using the pen.
The magnetic sketcher works on the same principle thanks to which the iron nails or powders orient themselves in the magnetic field. They get magnetised by the external field and follow the magnetic field lines. Such an aligned configuration has a lower energy than separate grains would have.
Iron nails are paralell to magnetic field. Such configuration creates smaller external magnetic field and it has smaller energy. Magnetization of the needles occurs along them not across
The magnetic dust in the sketcher is really microscopic. The magnetic pen brings it on the screen. The magnetic eraser attracts the dust and the picture disappears.
In this picture two magnets were positioned on the magnetic screen - one through a plate of normal steel, another through a plate made of a special magnetic alloy, called mu-metal. This material is characterised by very high magnetic permeability ((μR=20000, compared to pure iron (μR=500) and is used to shield magnetic fields. No Earth's magnetic field is present inside a box made of such a material. Geese travelling South in autumn and marine turtles coming back to beaches were they were born would get lost inside such a box.
