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PR108—Cadmium Red

Pigment Type

inorganic, cadmium

Chemical Name

cadmium sulfide and cadmium selenide

Chemical Formula

CdS × CdSe

Properties

Cadmium Red is a bright, warm red that ranges in shade from orange-red to maroon and is available in light, medium, and dark versions. It is strong and opaque, with good tinting strength. Cadmium Red dries slowly. It grays down when mixed with white, mixes well with blues to create a range of browns, and mixes well with Cadmium Yellow to create a strong orange. It also works well in neutral mixes. Cadmium pigments have been partially replaced by azo pigments, which are similar in lightfastness to the cadmium colors, cheaper, and non-toxic. Hues vary by brand.

Cadmium Red is usually available in either a pure grade or a cadmium-barium mix. The cadmium-barium mix has the same permanence as pure Cadmium Red, but it has a lower tinting strength.

Permanence

Cadmium Red is lightfast and permanent in most forms, but like many cadmium pigments, it will fade in fresco or mural painting. Its improved lightfastness has helped it to replace Vermilion on the artist’s palette.

Toxicity

Cadmium Red is a known human carcinogen. It is extremely toxic if inhaled and slightly toxic if ingested.

History

Cadmiums get their names from the Latin word cadmia meaning zinc ore calamine, and the Greek word kadmeia, meaning Cadmean earth, first found near Thebes, the city founded by the Phoenician prince Cadmus. Metallic cadmium was discovered in 1817 by Friedrich Strohmeyer, but Cadmium Red was not introduced until 1907 in Germany.

Alternate Names

Cadmium Scarlet, Selenium Red.

PR112—Naphthol Red AS-D

Pigment Type

organic, monoazo

Chemical Name

n/a

Chemical Formula

C₂₄H₁₆Cl₃N₃O₂

Properties

This Naphthol Red is an intense scarlet red pigment that is heavily staining. It has an average drying time. It is semi-transparent and has relatively poor covering power.

Permanence

This Naphthol Red has been rated as having excellent lightfastness under ASTM testing, but other testing methods have demonstrated some tendancy for the color to fade with exposure to strong ultraviolet light. It has been considered a replacement for less lightfast naphthol reds such as PR3. Not suitable for exterior use.

Toxicity

Naphthol Reds are not considered toxic. Naphthol Red AS-D may cause eye, skin, or respiratory irritation. Contact with dry pigment should be avoided.

History

Unknown.

Alternate Names

Naphthal, Naphthol Bordeaux, Naphthol Carbamide, Naphthol Carmine, Permanent Carmine, Permanent Red, Fanchon Red.