Fig. 1. (a) Infrared spectrum of white paper and black erasable pen of PILOT on glass and white paper; (b) Infrared spectrum of different brands of black erasable pen on glass; (c) Infrared spectrum of AIHAO brand erasable pen with different colors on paper; (d) Infrared spectrum of MG brand erasable pen with different colors on paper
The samples are labeled with the serial numbers in Table 1

Fig. 2. (a) Infrared spectrum of MG brand thermochromic erasable ink on paper before and after fading; (b) Infrared spectrum of uni film-forming brush ink on paper before and after fading

Fig. 3. (a) Correlation loadings from PCA of infrared spectra of AIHAO of erasable pen on different substrates for the first three principal components; (b) Principal component analysis results of AIHAO of different colors on paper and glass; (c) HEATMAP results of of AIHAO different colors on paper and glass

Fig. 4. (a) Correlation loadings from PCA of infrared spectra of black erasable pen for the first three principal components; (b) Principal component analysis results of black ink of different brands on glass

Fig. 5. (a) Correlation loadings from PCA of infrared spectra of different color of different brands erasable pens on glass for the first three principal components; (b) Principal component analysis results of different colors of different brands on glass; (c) HEATMAP results of different colors of different brands on glass

Table 1. Model list of erasable pen