A, reagent and solution analysis method, unless otherwise specified, only use analytical pure reagent and distilled water. Hydrochloric acid (GB 622); Sulfuric acid (GB 625); Potassium dichromate (GB 642); Acetone (GB 686). Dilute hydrochloric acid solution: it is made by mixing 1 part hydrochloric acid and 17 part distilled water. Cobalt chloride solution: it is prepared from 1 part by mass of cobalt chloride and 3 parts by mass of dilute hydrochloric acid solution. Ferric chloride solution: it is prepared from 5 parts by mass of ferric chloride and 1.2 parts by mass of dilute hydrochloric acid solution. Potassium chloroplatinate solution: weigh 790mg of potassium chloroplatinate in a 50mL beaker, accurate to 0. 1mg, and dissolve it with dilute hydrochloric acid solution. When dissolving, it can be heated slightly until the potassium chloroplatinate is completely dissolved. After cooling to room temperature, all of them are poured into a 100mL volumetric flask, diluted to scale with dilute hydrochloric acid solution, and mixed evenly. Second, the instrument's Nessler colorimetric tube: 25mL, tube diameter 20mm；; Analytical balance: sensitivity 0.1mg; ; Shelf balance: sensitivity 0.1mg; ; Volumetric flask: 25mL,100ml; ; Pipette: 0. 1 ml, 1 ml, 10 ml, 50 ml. Preparation of Gardner color standard solution/preparation of kloc-0/~ 8 color standard. According to the amount shown in the table below, transfer the potassium chloroplatinate solution to eight 25mL volumetric flasks with a pipette and dilute it with dilute hydrochloric acid solution to scale. The prepared solution is Gardner color scale 1 ~ 8. Compile color code 9 ~ 18. According to the amounts shown in Table 2, transfer the cobalt chloride solution and ferric chloride solution to the 10 100mL volumetric flask and dilute it with dilute hydrochloric acid solution to scale. The prepared solution is Gardner color scale 9 ~ 18. Storage of color codes. Matching Gardner color standards should be stored in the dark and checked with reference solution at least once every six months. 4. Sample: Dissolve 4 parts of epoxy resin in 6 parts of acetone. 5. Operating steps: pour the sample into a clean colorimetric tube, then place the colorimetric tube containing the sample side by side with the colorimetric tube containing Gardner color standard solution, and visually inspect the color from the side under the scattered light during the day. Note: Daytime scattered light refers to the light that comes in from the north-facing window from sunrise to 3 hours before sunset without direct sunlight. 6. The results show that the color of the sample is represented by the color code that is the same as or closest to the color of the sample solution. When a more accurate representation is needed, the degree of similarity should be stated. For example, when the color is between 5 and 6, it can be expressed as 5, 5+, 6- and 6 grades.