Pigment Yellow 42 is a chemical compound, known as yellow iron oxide, is chemically classified as an inorganic color. This pigment is mainly composed of hydrated ferrous oxide and is widely used in various industrial and cosmetic applications. 

Chemical Name

iron(3+);oxygen(2-);hydroxide;hydrate

It comes in the form of yellow powder.

Chemical Composition and Structure

Pigment Yellow 42 is an inorganic compound with the chemical formula FeO(OH)·H₂O. It consists chiefly of hydrated ferrous oxide, which is iron in the +2 oxidation state combined with oxygen and water. This composition gives the pigment its characteristic yellow color.

Physical Properties

This pigment typically appears as a fine yellow powder. It has a high density and excellent covering power. Pigment Yellow 42 is known for its chemical stability, resistance to light and heat, and inert nature, making it suitable for long-lasting applications. Its opacity and strong tinting strength make it a versatile pigment for various uses.

Chemical Industrial Synthesis Process

• Preparation of reagents. The main raw materials include ferrous sulfate (FeSO₄) and an oxidizing agent such as hydrogen peroxide (H₂O₂) or air.
• Synthesis of hydrated ferrous oxide. The production of Pigment Yellow 42 begins with the precipitation of hydrated ferrous oxide. Ferrous sulfate is dissolved in water and oxidized by adding an oxidizing agent.
• Formation of the precipitate. The solution is treated to form a precipitate of hydrated ferrous oxide (FeO(OH)·nH₂O), also known as goethite.
• Filtration. The resulting suspension is filtered to separate the solid precipitate from the aqueous solution.
• Washing. The hydrated ferrous oxide is washed with deionized water to remove any soluble impurities.
• Drying. The washed hydrated ferrous oxide is dried at controlled temperatures to remove residual moisture and obtain a dry powder.
• Grinding. The dried hydrated ferrous oxide is ground to obtain a fine and uniform powder. This step may involve the use of ball mills or other grinding machinery.
• Classification. The dried powder is classified to ensure a uniform particle size. This step may involve sieving or the use of air classifiers.
• Stabilization. The Pigment Yellow 42 powder is stabilized to ensure its stability during transportation and storage, preventing oxidation and aggregation.
• Quality control. The Pigment Yellow 42 undergoes rigorous quality testing to ensure it meets standards for purity, color intensity, and safety. These tests include chemical analysis, spectroscopy, and physical tests to determine particle size and rheological properties.

What it is used for and where

Cosmetics

Colorant. This ingredient has the function of colouring the solution in which it is inserted in a temporary, semi-permanent or permanent manner, either alone or in the presence of the complementary components added for colouring.

Restricted cosmetic ingredient as IV/136  a Relevant Item in the Annexes of the European Cosmetics Regulation 1223/2009. Substance or ingredient reported:

• Iron Oxide Yellow. Wording of conditions of use and warnings:  Purity criteria as set out in Commission Directive 95/45/EC (E172)

Pigment Yellow 42 is used in cosmetic products such as foundations, powders, eyeshadows, and blushes due to its warm yellow color and high opacity. It provides long-lasting color.

Industrial Applications

Paints and Coatings: In the paint industry, iron oxide yellow is used to achieve yellow shades and enhance UV resistance. Its stability and strong tinting properties make it ideal for both decorative and protective coatings.

Plastics and Polymers: This pigment is employed in the production of plastics and polymers to improve color uniformity and opacity. It is commonly used in products like automotive parts, packaging materials, and consumer goods.

Ceramics and Glass: Pigment Yellow 42 is used in the production of ceramics and glass to achieve stable yellow colors. It is particularly valued for its resistance to high-temperature processes.

Inks: The pigment is also used in printing inks to produce intense yellow colors, ensuring high-quality and durable prints.

Safety

Pigment Yellow 42 is generally considered safe for use in consumer products when handled according to proper safety procedures. It is important to avoid inhalation of the powder and minimize direct contact with skin and eyes (1).

Studies

Ultraviolet rays from the sun cause skin aging and smartphones emit high-energy visible light from which you should protect yourself. Iron oxides (yellow, red and black) in sunscreens have the property of effectively blocking high-energy visible light especially when combined with zinc oxide (1).

As regards food safety, being an additive also added in fruits and vegetables, for these foods a maximum permissible level of 6 milligrams per kilo body and the formula "enough" in 48 categories of food  (Regulation (EC) No 1333/2008). Within these categories of foods, iron oxides and hydroxides are allowed in liquid food supplements, food supplements in syrup, in solid form, including capsules and tablets and similar forms, excluding chewable. However, EFSA recommends further scientific analysis (3).

Molecular Formula FeH₃O₃

Molecular Weight   106.87 g/mol

CAS   51274-00-1 1345-27-3 20344-49-4 52357-70-7

EC number   257-098-5 215-722-3 215-570-8 257-670-1

UNII EX438O2MRT

DTXSID2029371

Synonyms:

Ferric Oxide Yellow

Iron Oxide Yellow

Yellow Iron Oxide

Pigment Yellow 42

CI 77492

References____________________________________________________________________

(1) Aquilina, G., Azimonti, G., Bampidis, V., de Lourdes Bastos, M., Bories, G., Chesson, A., ... & Wester, P. (2016). Safety and efficacy of iron compounds (E1) as feed additives for all species: ferric oxide based on a dossier submitted by Poortershaven Industriële Mineralen BV. EFSA JOURNAL, 14(6), 1-26.

Abstract. The additive under assessment, ferric oxide, contains between 57% and 69% iron (Fe). The EFSA FEEDAP Panel could not conclude on the safety of ferric oxide for the target animals owing to that (i) the application of ferric oxide red is for all animal species, (ii) lifetime administration to animals is not excluded and (iii) a sufficient biological and toxicological database was not available. Regarding (i) the very low absorption of iron from the ferric oxide by target animals and (ii) the homoeostatic regulation of iron metabolism in animals, any influence of feeding the ferric oxide on the iron content of edible tissues and products is not expected. The use of ferric oxide in animal nutrition is unlikely to result in a direct exposure of the consumer to this oxide. Consequently, the supplementation of feed for food-producing animals with ferric oxide would likely not constitute a risk to consumers. Ferric oxide is an irritant to skin and eyes by mechanical action. Owing to the nickel content in the additive, the ferric oxide

(2) Bernstein EF, Sarkas HW, Boland P. Iron oxides in novel skin care formulations attenuate blue light for enhanced protection against skin damage. J Cosmet Dermatol. 2021 Feb;20(2):532-537. doi: 10.1111/jocd.13803. 

(3) EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS)
First published: 08 December 2015 https://doi.org/10.2903/j.efsa.2015.4317