<prompt> Preferential contamination of direct filling gold is done by:Pure ethanol2 glutaraldehyde18 ammonia5 sodium hypochlorite  <response>: After pellets of gold are rolled, they may be conveniently stored in a gold foil box, which is divided into labeled sections for various sizes of pellets. Cylinders of foil and selected sizes of other types of gold also may be stored in the box. Preferential contamination is suggested by placing a damp cotton pellet dipped into 18 ammonia into each section of the boxThis serves to prevent deleterious oxides from forming on the gold until it is used.Key ConceptContamination of direct filling gold is done by 18 ammonia. Sturdevants art and science of operative dentistry. 7th edition page e69 