鐵粉

My kid’s science project needed a visual for magnetic field lines, and these fillings worked perfectly—they’re fine enough to show clear patterns with just a magnet. The small container lasted through multiple experiments, too.

Sprinkling these onto a piece of paper with a magnet underneath made the magnetic field lines instantly visible—exactly what I needed for a simple physics demo. The fine grains moved smoothly and settled into clear patterns, which was really satisfying to watch.