Fig. 1. Reproducibility experiment of 84^# samples

Fig. 2. Heat map of the relative content of fillers in black ink handwriting

Fig. 3. (a) Reproducibility results of 40^# sample in category Ⅰ; (b) Differential Raman spectrum of 28^# sample in category Ⅱ; (c) Differential Raman spectrum of 38^# sample in category Ⅲ; (d) Differential Raman spectrum of 21^# sample in category IV; (e) Differential Raman spectrum of 61^# sample in category V; (f) Differential Raman spectrum of 92^# sample in category

Fig. 4. Distribution of spectrally clustered samples

Fig. 5. Confusion matrix of feedforward neural network training results

Fig. 6. ROC curves of feed-forward neural network training results