Clay is a mixture of clay base and various mild abrasives. Clay along with a clay lubricant is used to remove paint contamination. Road grime, tar, bugs, rust, tree sap and even paint overspray can be removed with a clay bar. Clay bars differ in color and density but what is most important, type and amount of abrasive particles they contain. All clay bars will be labeled from "mild" to "strong" abrasive quality. Claying does not remove the clear coat of the paint but can cause marring or dullness if used incorrectly. When using a clay bar sufficient lubrication must be present to avoid scratching the paint. It takes a few passes of clay to feel the difference on the surface of the paint. To evaluate the effectiveness of claying dry the area and assess the paint and the bar. The paint should become slick to touch. The clay bar used should be turning gray. If the clay bar is dropped it must be discarded. The clay bar should be folded over frequently to expose clean surface. Claying does not replace polishing. It is a process that should be used before polishing compound is used. Claying should be used once or twice a year.
i cpoied and pasted that off of a definition i found
i used to work for the wash tub a local full service car wash - thats how i heard about it - works like a charm. i get the clay and lube from a my friend that still works there but im sure you can pick it up at a local retail and also you will have to wax immediatly afterwards for best results becuase the lube and clay leave a weird film on your ride.
but i bought this stuff last sunday by ICE(made by turtle wax) called liquid clay worked just aswell not so tidious like with the clay bar its important you do it in the early AM or early PM like wax and as stated make sure you dont get even the slightest bit of gravel or dirt form a single drop to the floor cuase it picks up everything and youll end up scratching your clearcoat or paint
sorry for the long post but i promise for those lsoing clear coats or those you just like to maintian their clear coat you will benefit from this