Indigo Blue Food Coloring

Blue food coloring came from indigo, or from Prussian Blue. Prussian blue originated in the early 1700’s, and the name is said to have come from the actual dye used to color the Prussian military uniforms. (Prussian Blue has been approved to help rid the body of radioactive contaminants, but the CDC has noted that the Prussian Blue coloring is not the same as the FDA approved compound Prussian Blue, i.e. you cannot self-medicate using artist’s colors.)

According to Wikipedia, the formula for Prussian Blue is:

Fe₇(CN)₁₈ 14H₂O

Indigo is made from plant extracts, and from synthetic processing.

For an updated post on how indigo dye is extracted, and more about blue food coloring in the past visit: Making Blue Food Coloring in Old Times on the main PastrySampler.com site.