Naphthol Red Deep: Spectroscopic Analysis Overview

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PR 170.1 – naphthol red deep

This page presents the Spectroscopic analysis of this pigment.
The pigment has been examined using XRF spectroscopy, Raman spectroscopy, FTIR spectroscopy, and Reflectance Spectroscopy. These complementary techniques provide valuable insights into the pigment’s composition and structure.
This page aims to show which analytical methods are most effective for identifying this pigment in artworks and historical materials. By comparing results across different techniques, it serves as a practical reference for Heritage Science, Conservation, and Pigment Analysis.

Manufacturer/ product code: Kremer / 23290
Chemical Description: naphthol AS
Color: red
Color Index: PR 170.1
Date: 1983

PR 170.1 – Naphthol Red Deep is a synthetic organic pigment belonging to the β-naphthol (monoazo) pigment family, widely used for its intense color strength and characteristic deep red hue. Developed in the 20th century as part of the expansion of azo pigment technology, PR 170.1 became a popular choice for applications requiring strong, economical reds with good saturation.

In color, PR 170.1 appears as a deep, slightly bluish red, often described as a crimson or deep carmine. It offers high tinting strength and is typically semi-opaque, providing solid coverage in masstone while still allowing some control in mixtures. Compared to lighter naphthol reds, the “deep” designation reflects its darker tone and increased depth, making it useful for rich reds, shadows, and dark mixtures. When combined with warm yellows, it produces strong oranges, while mixtures with blues or blacks yield deep violets and neutralized browns.

Technically, PR 170.1 shows good resistance to heat and chemicals and moderate to good lightfastness, depending on formulation and medium. It is widely encountered in printing inks, plastics, and coatings, where color strength and cost efficiency are critical. In artists’ paints, PR 170.1 is valued for its powerful chroma and expressive depth, though it is generally considered less permanent than quinacridone or anthraquinone reds.