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> The same also applies to aluminum, magnesium, nickel, etc. the oxides of aluminum, magnesium, and nickel were not in use as paint pigments > What distinguishes iron and copper from aluminum and titanium is the energy required to split the oxide into metal. (...) Titanium is not more reactive than aluminum the particularly relevant issue here, as i understand it, is that titanium has a stable carbide, which prevents you from reducing it carbothermically; you end up with titanium carbide instead of titanium metal. aluminum's carbide is unstable even in water, while iron's carbide is mechanically strong but still easy to reduce to iron with air. copper's carbide is poorly characterized and even more unstable, and it even occurs native there are other things that titanium reacts more strongly with than aluminum does. titanium tetrachloride, for example, which is mentioned in the article, isn't a mere salt like normal chlorides; it's a volatile fuming liquid, because titanium forms covalent bonds with the chlorine like a motherfucking nonmetal. you can argue about whether this makes it more or less reactive than aluminum in this context; the reaction produces more energy per metal atom but less energy per chlorine atom this kind of dirty trick is why titanium wasn't isolated until decades after the creation of metallic calcium, sodium, potassium, aluminum, and even the isolation of some of the rare earths so i think the characterization in the article is fair |
Aluminum oxides were used as a pigment, predominantly in blue (cobalt aluminum oxide) but also in white.
In any case, the dominant white dyes of the Early Modern period -- and prior periods -- were lead based. The presence of TiO2-based pigments is actually one good way to identify a modern forgery.
> the particularly relevant issue here, as i understand it, is that titanium has a stable carbide
This turned out to be solvable via calciothermic or magnesiothermic reduction -- which is now effectively the go-to method for just about everything that can't be reduced with carbon. All titanium dioxide reduction processes demand quite a lot of energy, though; more than aluminum and far more than iron.