Many Plastic converters purchase plastic concentrate in master batches pre-tinted from their suppliers. Lot to lot consistency of the plastic concentrate is extremely important. Most converters can only control their product color by adjusting the ratio of Plastic concentrate to raw resin as the hopper feeds into the press. Plastic converters rely on colorimetric data supplied by their concentrate manufacturer. Color concentrate manufacturers provide color data measured from plastic plaques formed under tightly controlled conditions in their laboratory. Plastic converters often don't have the time or equipment to recreate the plaques for incoming quality control. This means converters either accept the colorimetric values shown on their certificate of analysis provided with incoming shipments or they can establish tolerances on the raw plastic concentrate. Careful consideration of sample presentation must be followed to ensure repeatable results. Plastic concentrate has few of the qualities desirable for easy color measurement. Below is a listing of some of the qualities that make plastic concentrate difficult to measure.