Silver streaks are the splash appearance of moisture, air, or charred plastic particles on the surface of a moulded part, which are fanned out in a direction emanating from the gate location.

Causes of silver streaks
Silver streaks can be caused by:

• Moisture - Plastic materials absorb a certain degree of moisture during storage. If the material is not dried properly before moulding, the moisture residing in the resin will turn into a steam during the injection process and splay on the surface of the moulded part.
  
  
• Air - During the plasticization period, a certain amount of gas can be trapped and blended into the melt material. If the air does not escape during the injection process, it could splay out on the surface of the moulded part.
  
  
• Degraded (charred) plastic particles - There are a couple of reasons degraded (charred) plastic particles will splay on the surface of a moulded part.
  
  
• Material contamination - When moulding with two materials, as you switch from one material to another, the residual particles left in the barrel could be charred if the second material is being moulded at a higher temperature. In addition, contaminated, rejected parts and regrind will re-contaminate virgin material in the next batch of moulded parts.
  
  
• Barrel temperature - Improper barrel temperature setting may degrade polymer molecules, and they will begin to char.
  
  
• Shot volume - If the shot size is below 20 percent of the machine injection capacity, especially for temperature-sensitive materials, the melt resin will remain in the barrel too long and will begin to degrade.