To avoid putting your fingerprints on evidence or getting blood from evidence on your hands, hold the evidence with tweezers. Nickel-plated tweezers can be cleaned in alcohol or other solvents or can be autoclaved. Do not use metal tweezers while processing with Physical Developer, instead use the polystyrene tweezers. However, some solvents in DFO or Ninhydrin may damage the polystyrene tweezers. They are great for handling bloody items and then discarded.