The use of a gloss meter in evaluating the surface gloss of printing paper and art paper.

Rationale

A gloss meter is an optical instrument that quantifies gloss by measuring the ability of an object to reflect light. Its working principle is based on standard geometric conditions, typically measured at angles of incidence of 20°, 60°, and 85°, and is suitable for high, medium, and low gloss surfaces, respectively. The instrument emits a beam of light from a standard light source to the surface of the sample, receives the reflected light flux in the direction of the specified reflection angle through the detector, and compares it with the reflected light flux of a polished black glass standard plate with a refractive index of 1.567 under the same conditions, and calculates the gloss value in GU (Gloss Unit). Its basic calculation formula can be expressed as:

G = (R_s / R_0) × 100

where G is the gloss value of the sample, R_s is the reflected luminous flux of the sample surface, and R_0 is the reflected luminous flux of the standard plate under the same conditions.

The surface gloss characteristics of printing paper and art paper

The surface gloss of printing paper and art paper is a key indicator of their visual and tactile quality, directly affecting the color performance, layering, and overall aesthetic effect of printed materials. The luster of printing paper is usually related to the coating process, and the surface of the coated paper is smooth, which can produce high specular reflection. Art paper covers a wider range of surface treatments, such as embossing, suede, pearlescent, etc., and its luster performance is often non-uniform or diffuse reflection dominant. The difference in gloss characteristics between these two types of paper determines the need to choose different measurement angles and evaluation strategies when measuring.

The selection basis of the measurement angle

The choice of measurement angle depends on the estimated gloss range of the paper surface. For printing paper such as high-gloss coated paper, it is recommended to use a 20° angle for measurement, which has a strong resolving power for high-gloss differences. For ordinary glossy offset paper, etc., the 60° angle is the general angle. For low-gloss or matte art papers, such as rough paper or some specialty papers, an 85° angle should be used to enhance the measurement sensitivity of the low-gloss range. For samples with unknown gloss, a preliminary determination can be made at a 60° angle, and then the angle can be adjusted according to the results.

Operation process

To ensure repeatability and comparability of measurement results, standardized operating procedures should be followed. First, the gloss meter needs to be calibrated, using the included standard calibration plate. When measuring, ensure that the paper sample is flat, clean, free of creases, and covers the measuring hole area. Pay attention to environmental conditions and avoid direct bright light or drastic changes in ambient light. The measurement position should avoid paper diseases or obvious texture inconsistencies. For samples with uneven surfaces, such as art paper, they should be measured and averaged at multiple representative locations. Key factors affecting measurement results include the flatness and uniformity of the paper surface, ambient temperature and humidity, the contact pressure between the instrument and the sample, and the calibration status of the instrument.

Application scenarios

The measured gloss value needs to be interpreted in conjunction with specific application scenarios. In the printing industry, gloss data is used to predict the visual effect of inks after they have dried, control batch consistency, and match customer-specified gloss requirements. For art paper, gloss evaluation is more used to describe and classify its unique visual texture, such as velvet, metallic or natural texture. A single gloss value may not be sufficient to fully describe the complex appearance of art paper, sometimes in combination with other visual indicators. The following table lists the typical gloss ranges for different types of paper in relation to the main applications:

Notes:

Gloss meters have certain limitations in evaluating complex surfaces. The instrument measures the specular gloss under specific geometric conditions, and for the strong diffuse or directional textures of art paper (e.g., brushed, long lines), a single value may not fully reflect the overall gloss impression perceived by the human eye. In addition, color, grain depth, and surface pattern can interfere with measurements. Therefore, in quality control, gloss data should be used as an important but not the only objective indicator, which often needs to be combined with subjective visual evaluation. During operation, it is necessary to calibrate the instrument regularly, use a unified measurement protocol, and analyze the abnormal data to check whether it is caused by the local characteristics of the paper or the measurement operation.

Summary

Gloss meters provide an objective and quantitative means for the evaluation of the surface gloss of printing paper and art paper, and are an important tool for quality control and product development in the papermaking, printing and packaging industries. By understanding the principles, selecting the appropriate measurement angle according to the standard, and standardizing the operation process, reliable data can be obtained. At the same time, it recognizes its limitations in evaluating the surface of complex art paper, combined with subjective evaluation, to make a comprehensive and accurate judgment on the surface visual quality of the paper.

References

ASTM D523 Standard Test Method for Specular Gloss

ISO 2813 Paints and varnishes — Determination of gloss value at 20°, 60° and 85°

TAPPI T480 om-15 Specular gloss of paper and paperboard at 75°

Relevant literature of the national standard of "Printing Technology Printed Matter and Printing Ink Gloss Determination"