Measurement of wet color and gloss change of gravels during drying

Abstract

　The color changes during drying were investigated for white, red and gray gravels. After taking them out from water, their colors were measured using a digital camera within 1 minute, at five-minute intervals for the first 60 minutes, at ten-minute intervals until 90 minutes, and at 120 minutes. Gravels were dried at room temperature 23±1 ℃ and relative humidity 50±5 %. Then, the small color change arose after 80 minutes for white. For red and gray, the large changes occurred from immediately after elapsed out of the water until 30 minutes, and the change appeared again after 70 minutes. When the lightness of gravel was low, such as red or gray, diffuse reflections near the surface were suppressed and the lightness was further reduced, whereas when the lightness was high, such as white, the effect of wetting tends to be diluted because the rate of light absorbed by the gravel was small.