Dear Dr. Riva:
In a general way, red pigments are based on one of compounds: red-lead, iron oxide, red of cadmium. Nowaday, lead (Pb) and cadmium (Cd) exert further environmental problems.
i) The paper can be read to gain some inspiration, below some data:
Preparation of yellow and red iron oxide pigments from iron(II) sulfate by alkali precipitation
Thermochimica Acta Volume 77, Issues 1–3, 15 June 1984, Pages 177-184
Abstract
A study was made of the preparation of yellow α-FeOOH pigments from iron(II) sulfate solution by alkali precipitation and gas oxidation methods. The preparation of pure yellow pigments turned out to be difficult. Pigments of composition FeOOH were obtained under acidic (pH < 5) and alkaline (pH ⪢ 12) conditions at temperatures below ambient. In slightly alkaline solution some Fe3O4 was formed as well, and it stained the products greenish, brownish or black. At 70°C and pH 7–9 a pure black Fe3O4 was formed.
According to TG measurements, the needle-like FeOOH particles decomposed to red α-Fe2O3 above 300°C and the pigments then obtained were light red. The preparation of dark red oxides required higher temperatures than the direct firing of FeSO4•7 H2O to oxide.
site:
http://www.sciencedirect.com/science/article/pii/0040603184870562
ii) Consider to access an interesting site via link:
site:
http://www.oilfieldwiki.com/wiki/Iron%28III%29_oxide
iii) There is a great number of Patents at about this Kind of pigment, consider see two in attach.
iV) Also, the interesting paper at about preparations route and strategies of color changing. Pdf copy in attachment.
Best regards
Marcos Nobre
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