Quantitative analysis of mixed pigments for Chinese paintings using the improved method of ratio spectra derivative spectrophotometry based on mode

Abstract

Background: Mixed pigment analysis is an important and complex subject in preserving and restoring Chinese paintings since the colors observed by our naked eyes or instruments such as hyperspectral cameras are usually a mixture of several kinds of pigments. The purpose of this study was to explore a more effective method to confirm the type of every pure pigment and their proportion in pigment mixtures on the surface of paintings. Methods: Two endmember extraction algorithms were adopted to identify the types of pigments and an improved method of ratio spectra derivative spectrophotometry was used to determine their proportion. Main works: (1) Extracting the pure pigment components from mixed spectrum by adopting two blind source separation algorithms: Independent Component Analysis and Non-negative Matrix Factorization; (2) matching the separated pure spectrum with the pigment spectral library built in our laboratory to determine the pigment type; and (3) calculating the proportions of mixed pigments using the Ratio Spectra Derivative Spectrophotometry based on Mode, which is improved based on the original algorithm. Finally, a comparison was made with two abundance inversion algorithms: Least Squares Algorithm and Minimum Volume Simplex Analysis. The correlation coefficient and root mean square error were used to provide evidence for accuracy evaluation. Conclusions: (1) Non-negative matrix factorization is more suitable for endmember extraction; and (2) Ratio spectra derivative spectrophotometry based on mode is more suitable for abundance inversion.

Analytical Approach for the Study of Teotihuacan Mural Paintings from the Techinantitla Complex

“…The small blue area analyzed is adjacent to a red area, and the presence of a mixture or a superimposition of layers cannot be discarded. This effect on the reflectance has been observed for mixtures of azurite and orpiment [46]. The presence of red earths would also explain the weak reflectance maximum at 604 nm, observed on the spectrum of the blue area.…”

Non-Destructive Prediction of the Mixed Mineral Pigment Content of Ancient Chinese Wall Paintings Based on Multiple Spectroscopic Techniques

“…[18][19][20][21] However, the current methods used to quantitatively analyze mixed pigments in ancient wall paintings are still very limited. Hyperspectral imaging techniques have been validated for predicting the relative pigment contents in previous studies, but complex mathematical methods are still required to indirectly identify the types of pigments, 22 and thus it is not possible to rapidly and accurately obtain the pigment chemical compositions. Furthermore, the effects of binding materials and degradation due to aging on the predicted relative contents of mixed pigments were not adequately considered in previous studies.…”