Spectrophotometer for testing the color of gold and silver cardboard

Surface Optical Characteristics of Gold and Silver Cardboard

When the incident light hits the surface of an object, the spatial distribution of the reflected light will vary with the smoothness of the surface. For gold and silver cardboard, its surface is not only coated evenly, but also contains flake-shaped metal particles in the coating layer, which has great directionality in the reflection of light. Therefore, when the incident light is irradiated, the surface of the gold and silver cardboard will have a strong specular reflection. This very non-uniform spatial distribution feature causes the color appearance of its surface to change with the viewing angle.

Color Measuring Instruments

In color measurement technology, existing color Measurement Instruments include Spectrophotometer s with different geometric light paths such as 0:45°, multi-angle and d:8° (also known as integrating sphere ) .

The 0:45° instrument mainly has two measurement methods, one is 0° incident light, which accepts 45° reflected light, and the other is 45° incident light, and 0° angle receives reflected light. The measurement principle is shown in Figure 1 (One measurement is shown here).

The multi-angle Spectrophotometer mainly measures the values of 5 angles of 15°, 25°, 45°, 75°, and 110°.

The basic principle of the integrating sphere measuring instrument is: the light is irradiated vertically on the measuring object, and the reflected light is uniformly reflected in the integrating sphere (the inner surface of the integrating sphere is made of a completely reflective diffuse material, and the light can be reflected back and forth) and then received at a single angle. . It is equivalent to a uniform sphere emitting light, illuminating the surface of the measuring object, and measuring its spectral reflectance. Generally, a gloss absorption trap is installed inside the sphere opposite to the receiving angle. When the gloss absorption trap is turned on, any specular reflection can be reduced to a minimum. This measurement method is called "specular exclusion" (SPEX) . The results are similar to the measurement results of the above-mentioned 0:45° instrument. When we measure the color appearance of a high-gloss surface and need to consider the gloss effect of specular reflection, the glossy absorption trap is turned off and the "specular reflection included" method is used for measurement (SPIN).

Color Measurement Method

The gold and silver cardboard used as the base material requires uniform color characteristics. And for the visually uniform color of the base material, its color measurement can also give a uniform and consistent characterization. An effective color measurement and characterization method should firstly give consistent measurement values for different positions of a uniform color sample, as well as multiple measurement values at the same position. Second, the size of the color measurement should reflect a reasonable variation in color.

Experimental sample

The samples selected for the experiment are three types of cardboards: high-gloss gold cardboard, high-gloss silver cardboard and semi-gloss silver cardboard, and several different samples are selected for numbering in each type of cardboard. The sample numbers are high-gloss gold cardboard J1~J6, high-gloss silver cardboard Y1~Y6, and semi-gloss silver cardboard bY1~bY5. The visual evaluation experiment of the brightness was carried out on the three groups of samples, and the order of the brightness was determined. The results are: the high-gloss silver cardboard is the brightest, the high-gloss gold cardboard is next, and the semi-gloss silver cardboard is relatively the darkest.

The experiment will first examine the consistency of instrumental measurements. The method is: use the three instruments in section 2.2 to select 10 points on each uniform color sample, and measure them evenly distributed between points. Secondly, it will be compared whether the magnitude relationship of the measured values of the instruments for each sample conforms to the aforementioned magnitude relationship of visual brightness perception.