Alternative to lead crowns
Lead chromates are lead chromates (PbCrO4) with lemon-yellow, yellow, orange, or red coloration. Yellow lead chromates are either pure lead chromate (PbCrO4) or an isomorphic mixture of lead chromate and lead sulfate (PbCrO4-n PbSO4). The color depends on the sulfate content — the higher the sulfate proportion, the lighter the pigment.
Main advantages: relatively low cost and high hiding power.
Main disadvantages: high toxicity, low color purity, and chemical instability.
Examples:
– when exposed to alkalis, lead chromates turn red due to the formation of basic lead chromates, making them unsuitable for concrete, plaster, and paving tiles;
– when exposed to hydrogen sulfide, chromates darken due to the formation of lead sulfide, making them incompatible with sulfur-containing materials;
– in oil- and alkyd-based coatings, chromates gradually change hue: they turn green (Cr6+ → Cr3+) and darken due to the formation of lead peroxides.
Lead chromates are toxic substances — hazard class 1. Lead compounds contained in chromates can affect the central nervous system and blood when ingested. Lead tends to accumulate in the body in the form of insoluble compounds and may remain for decades.
As an alternative to lead chromates, we offer organic pigments. Based on a series of tests and a combination of coloristic, performance, and economic factors, the most suitable substitute for lead chromates in alkyd paints is the yellow azo pigment of class 2. It is used in the paint and printing industries, as well as in the production of water-based pigment pastes.
A comparative pigment assessment was conducted. A Chinese-made yellow lead chromate pigment without calcite or other filler impurities (with chromium compound content above 28%) was used as the reference. Color comparison was carried out in accordance with GOST 11279.1–83 in a natural linseed oil-based coating, with a pigment-to-zinc white ratio of 1:20.
As shown in the table, Yellow Pigment 2 exceeds Medium Yellow Chromate in relative tinting strength by more than two times. Compared to inorganic pigments, Yellow Pigment 2 — like most organic pigments — is “softer,” requiring less energy for dispersion. Its bright, pure tone allows for a broad color range (including RAL catalog shades), which cannot be achieved with chromates.
For further comparison, model enamels were formulated under lab conditions to simulate alkyd enamel PF-115. Enamel No. 1 used Medium Yellow Chromate (7%), and Enamel No. 2 used Yellow Pigment 2 (2.8%). Detailed formulations are shown in the table:
The following table presents a comparative analysis of the coloristic properties of the two enamel samples:
The data clearly demonstrate that, with significantly lower pigment consumption, Yellow Pigment 2 enables the production of enamels with brighter, purer, and more saturated tones — without containing lead or hexavalent chromium. The lower usage rate offsets its higher cost, while also reducing dispersion costs. The overall economic benefit is estimated at 8–10%.
One of the key goals of the study was to identify an organic pigment with coloristic properties closest to currently available chromates. When matching specific enamel shades, other types of yellow organic pigments may be used, such as lightfast yellow or Yellow Pigment 3 in various combinations.
LLC “Pigment-Dnipro” guarantees the stability of pigment color properties, as production complies with international standards and modern instrumental methods of color assessment. High consistency in color ratings enables the use of these organic pigments in tinting paste production.