Anodizing can produce yellowish integral colours without dyes if it is carried out in weak acids with high voltages, high current densities, and strong refrigeration. Shades of colour are restricted to a range which includes pale yellow, gold, deep bronze, brown, grey, and black. Some advanced variations can produce a white coating with 80% reflectivity. The shade of colour produced is sensitive to variations in the metallurgy of the underlying alloy and cannot be reproduced consistently.
Anodizing in some organic acids, for example malic acid, can enter a runaway situation, in which the current drives the acid to attack the aluminium far more aggressively than normal, resulting in huge pits and scarring. Also, if the current or voltage are driven too high, burning can set in; in this case, the supplies act as if nearly shorted and large, uneven and amorphous black regions develop.
Integral colour anodizing is generally done with organic acids, but the same effect has been produced in laboratories with very dilute sulfuric acid. Integral colour anodizing was originally performed with oxalic acid, but sulfonated aromatic compounds containing oxygen, particularly sulfosalicylic acid, have been more common since the 1960s. Thicknesses of up to 50 μm can be achieved. Organic acid anodizing is called Type IC by MIL-A-8625.