1. Appearance: If the paper is stark white, it indicates an improper balance of protective and thermal coatings-likely due to excessive fluorescent whitening agents; high-quality paper should have a slight greenish tint. A lack of smoothness or an uneven appearance suggests an inconsistent coating. Similarly, if the paper is highly reflective, it contains too much fluorescent agent and is of inferior quality.
2. Heat Test: A simple method involves heating the back of the paper with a lighter. If the paper turns brown upon heating, the thermal coating formula is likely suboptimal, suggesting a shorter shelf life. Visible fine streaks or uneven color patches in the darkened areas indicate an inconsistent coating. High-quality paper should turn a dark greenish-black (with a hint of green) and exhibit uniform coloration, with the shade gradually fading from the center outward.
3. Sunlight Exposure Test: Mark the printed paper with a highlighter and expose it to direct sunlight (this accelerates the thermal coating's reaction to light). The paper that darkens the fastest has the shortest shelf life.