Naphthol Green: A History and Application Guide - Cultural Heritage Science Open Source

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PG 12 – naphthol green

Created in 1883 by Otto Hoffmann and still in use. It is mostly applied in the textile industry and coloring paper but has been used also for artists’ supplies (Windsor & Newton watercolors) from its early discovery. Though it is not among the most stable green dyes, it was appreciated in order to replace the even less lightfast natural green colorants.

Manufacturer/ product code: Sigma-Aldrich / N7257
Chemical description: iron complex of 1-nitroso-2-naphthol-6-sulphonic acid. C30H15FeN3Na3O15S3 . Acid Green 1 (C.I. 10020, AG1) Sigma-Aldrich CAS: 19381-50-1
Color: green
Color Index: PG12
More info:

PG 12, known as Naphthol Green, is a synthetic organic pigment belonging to the class of naphthol-based azo pigments. PG 12 is characterized by a deep, cool green hue with moderate opacity and strong tinting strength, making it suitable for a variety of artistic, industrial, and commercial applications.

Chemically, PG 12 is formed by coupling a naphthol derivative with a diazo component, followed by precipitation to produce an insoluble pigment. This conversion from a soluble dye to a pigment enhances its stability and usability in different media, including oil, acrylic, tempera, and printing inks. Its transparency and clean chroma allow artists to mix it with other pigments to produce nuanced greens or muted tones, while its durability makes it a reliable choice in modern materials.

From a conservation standpoint, PG 12 is more stable than many early organic dyes, though it can exhibit moderate sensitivity to strong light and oxidizing conditions, potentially leading to fading or slight color shifts. As an organic pigment, it is not detectable by elemental techniques such as XRF, and identification relies on molecular methods, including Raman spectroscopy, FTIR, or chromatographic analysis. Its presence in an artwork is a clear indicator of 20th- or 21st-century materials, reflecting the adoption of synthetic organic pigments in modern color palettes.

W. Neugebauer, et al., Naphthol Green – a forgotten artists’ pigment of the early 20th century. History,
chemistry and analytical identiﬁcation, Journal of Cultural Heritage (2018).

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The Conservation & Art Materials Encyclopedia Online (CAMEO) is a comprehensive, searchable resource providing detailed technical information on materials (pigments), techniques, and tools used in art conservation, preservation, and scientific analysis.

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Open-access database of FTIR and Raman spectra for cultural heritage materials. Includes many historical pigments, dyes, and binders.