6.1.2 Freeze-thaw cycle
From the daily temperature variation in Niche of Sakyamuni Entering Nirvana (Chen et al., 2004), the temperature rose after 9:00; peaked around 15:00-18:00; gradually decreased, and stabilized about 22:00-9:00. As a result, the samples of freeze-thaw cycle were divided into two groups: saturated group (SG) and dry group (DG). All samples were oven-dried at 40℃ (9:00-19:00); the saturated group was saturated in the container (19:00-22:00), and the dry group was placed in the air; they were then placed in the freezer at -5℃ at 22:00-9:00. That corresponded to the completion of a cycle, and seven cycles were set as one period, as shown in Fig. 6.