Spectral Reflectance (350–2500 nm) Properties of Historic Artists' Pigments. II. Red–Orange–Yellow Chromates, Jarosites, Organics, Lead(–Tin) Oxides, Sulphides, Nitrites and Antimonates
Bibliographic record
Abstract
Unprocessed and minimally processed earth materials have been the traditional source of artist's pigments, dating back to prehistory. Identifying pigments comprising a cultural artefact has important conservational, scholarly and historic applications. In this study, we focus on red–orange–yellow historic artists' pigments that are not coloured by iron oxyhydroxides; specifically chromates, jarosites, organics, oxides, sulphides, nitrites and antimonates. We searched for specific spectroscopic characteristics that can be applied to their identification and differentiation from other pigments, with an emphasis on the less well studied near infrared region ( ca 1000–2500 nm). We combined and compared reflectance spectroscopy (350–2500 nm) with X-ray diffractometry for this purpose. It was found that these two analytical techniques are often complementary. Chromate, lead oxide, lead–tin oxide, lead antimonate and sulphide reflectance spectra are characterised by an absorption edge in the visible region as their only or main diagnostic spectral characteristic. While this pigment grouping can be recognised by the lack of additional spectral features, the presence of organic binders adds additional spectral features that can complicate their identification. Other techniques, such as Raman or infrared spectroscopy, are better suited for their non-destructive identification. Organic-derived pigments also exhibit an absorption edge but with additional spectral features that may allow for their unique identification. However, all pigment identifications can be complicated by absorption features associated with organic binders. Yellow earths which derive their colour from the mineral jarosite possess multiple diagnostic absorption bands that can be used for their unique identification. Cobalt yellow possesses minor absorption bands in the 2400–2500 nm region that may allow for its unique identification.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".