It is an way of explaining new to children. This tool is for discovering and observing new things. It is not messy and kids will love playing with it. You can find encased in the green film millions of magnetic particles suspended in oil. A great tool for science lovers, the film will change shades when magnetic fields are applied and it turns darker when field lines are perpendicular to the surface and it turns lighter when the are horizontal. Perfect for people passionate about science Easy to use, can be wrapped around objects Flexible and NOW and you'll fall in love instantly with this Magnetic Film Viewer Magnetic Field Viewer: position the viewing film (green area) on top of any magnet to discover where magnetic poles are located and how many it has. The area between magnetic poles is indicated by a light green "", while the poles themselves appear dark green color:Dark green Material:Magnetic Nanoparticles size:15cm x 10cm Package Contents: 1 x magnetic wall mount Only the above package content, other products are not included. Note: Light and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.