A ferrofluid is basically a bunch tiny iron fragments which are magnetic and suspended in oil. The oil will help keep the magnetic fragments from clumping. This solution is commonly found in many applications which you probably use everyday. Some applications include CDs, DVDs, sensors, radio speakers and more. If the item is not used, the fluid will eventually evaporate over time. Keeping it tightly sealed will help to prevent evaporation and prolong the fluid?s life so that it can be used again.