Coloring agents iron oxides

As a soil develops, OM decomposes to produce humus, which is black. Additionally, release of iron from minerals by weathering yields various reds and yellows. Both mechanisms yield soil coloring agents. Under oxidizing conditions, where soil is not saturated with water, the iron will be oxidized and thus in the ferric state [Fe(III)]. When the iron and OM are deposited on the surfaces of sand, silt, clay, and peds, they develop a coat that gives them a surface color. However, soil color is not only a surface characteristic but extends through the soil matrix. Under oxidizing conditions, soil has a reddish color. The chroma of this color depends to some extent on the amount of and the particular iron oxide present. 

Consumer articles often use colorants (qv), reodorants, or finishing agents. Carbon black (qv) provides the best technological properties for industrial appHcations, so most mbber articles are black. Red iron oxide or other inorganic pigments are used to color mineral-filled articles. Organic... 

Parabens are approved for use in oral solution and suspensions at a concentration of 0.015% to 0.2% w/v. Due to their low solubility, the sodium salts of parabens are often used in aqueous formulations. The parabens are most effective in the pH range of 2 to 6, and their antimicrobial activity decreases with increasing pH. Additionally, they are very unstable at pH 8 or above in solution. Methyl paraben has also demonstrated incompatibility with sorbitol and may show some discoloration in the presence of iron. The absorption of methylparaben by plastics has been reported with the amount absorbed being dependent upon the type of plastic and vehicle. However, no absorption has been reported for low density polyethylene (LDPE) or high density polyethylene (HDPE) containers. Certain coloring agents such as yellow iron oxide, ultramarine blue, and aluminum silicate can extensively absorb ethyl paraben in simple aqueous systems, thus reducing its preservative efficacy. 

Coloring agents can be either organic or inorganic, but the former can adversely affect heat stability. Examples of suitable inorganic colorants are oxides and salts of iron, chromium, cobalt, titanium, and cadmium. Some not only provide color, but can also have some beneficial heat-aging effects. 

Ocher is a weak tinting agent and is often replaced by synthetic hydrated yellow iron oxides for brighter color and better uniformity. 

Usually, iron oxide is added to glasses as a coloring agent or it can be present because of impure batch components. If the analyte solution is 0.05 M in H3P04, iron produces a stable and reproducible AAS signal with a stoichiometric to oxidizing air + C2H2 flame. 

In borosilicate glasses, the amber color is developed through interaction between iron oxide and titanium oxide or iron oxide and manganese oxide. Reducing agents are not used in borosilicate glasses for color development. Borosilicate ambers are called oxidized ambers. 

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