Paper whiteness

Paper whiteness refers to the degree of whiteness in paper, representing the total diffuse reflection of visible light across all wavelengths. The primary factors affecting whiteness are the lignin content in the paper pulp and the degree of bleaching. Since lignin has a yellowish hue, achieving high whiteness in paper requires minimizing lignin content. Paper whiteness significantly impacts the color reproduction range of the final printed product. Higher whiteness enables more accurate reproduction of ink colors, resulting in more vibrant colors and a broader color gamut in the final print. Newsprint typically has lower whiteness and a yellowish appearance, while offset paper and coated paper exhibit higher whiteness. IX. Opacity This property refers to the absence of show-through when printed text or images appear on one side of the paper while text or images are printed on the other side. High opacity in quality paper allows readers to focus on the content within the page itself, preventing eye strain caused by faint visibility of the printed image on the opposite side. Factors affecting opacity include: i. Paper thickness; ii. Coating presence; iii. Surface smoothness or roughness; iv. Plant fiber content. Testing involves measuring light transmission through the paper, expressed as a percentage.