A dark blue or purple dye extracted from logwood or brazilwood that is used in microscopy to stain cells and tissues, particularly for visualizing blood cells.
From haema (blood) + -ein suffix (organic compound), named because it was discovered through blood staining. Logwood trees from Central America were the original source in the 17th century.
Haematein is actually what you get when you oxidize haematoxylin—basically it's the active dye! For centuries, logwood chips were so valuable for dye that they were literally worth trading for—medieval European weavers paid premium prices for this blood-red color.
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