1. Appearance: If the paper is very white, it indicates an improper protective coating and thermal coating, suggesting excessive fluorescent powder. Good quality paper should have a slightly greenish tint. Uneven or poorly smooth paper indicates an uneven coating. Paper that reflects light strongly also indicates excessive fluorescent powder and poor quality.
2. Heat Test: Heat the back of the paper with a lighter. If the paper turns brown after heating, the thermal formula is flawed, and its shelf life may be short. If the black areas have fine streaks or uneven color patches, the coating is uneven. Good quality paper should turn a dark greenish-black (with a hint of green) after heating, with even color patches that gradually fade from the center outwards.
3. Sunlight Comparison: Apply a highlighter to the printed paper and place it in sunlight (this accelerates the thermal coating's reaction to light). The paper that turns black the fastest has a shorter shelf life.