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Oxygenated blood is bright red and deoxygenated blood is dark red or brown.

If you take oxygenated blood and leave it in the air it will turn dark red, then brown, then finally a bluish green from exposure to atmospheric oxygen.

Why does it oxidize this far to get a copper oxide color to it after it has passed the phase where it is the same color as iron oxide? Why doesn't it stay at the iron oxide color?

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green sounds like a copper compound, but I would have thought iron would be present in far higher levels than copper in the blood. Never seen blood turn green, but I don't have that much just laying around. How do you get it to turn green? – user137 Aug 10 '14 at 3:39
often during the last few days of my period it is extremely light bleeding and the blood is brown. After hours of extremely light bleeding it slowly goes from being reddish-brown like iron oxide to bluish-green like copper oxide. Because the 3rd stage of oxidation is so slow I don't see much green blood after 24 hours of extremely light bleeding but I do see more than I did in the few hours that it took to start that stage of oxidation. – Caters Aug 10 '14 at 4:46

Apparently there is a rare condition, sulfhemoglobinemia in which sulphide ions or H2S combine with the haem group in haemoglobin, causing a greenish colour. This can be related to certain drugs being present in the blood.

See here for an example in which surgeons discovered dark green blood in their patient.

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well I think in the case of myself that I don't have H2S in the blood and it is a light bluish-green I get after hours of oxidation of reddish brown blood so atmospheric oxygen can slowly oxidize blood from the iron oxide color(that reddish brown) to a copper oxide color(the light bluish green). Thats what I notice during the end of my period where the bleeding is extremely light and sometimes not constant is slow oxidation to a bluish green – Caters Aug 10 '14 at 13:26
But the colour of oxidised blood (ferrihaemoglobin) is established, and there isn't another oxidation stage to go to in the context of the protein. If the Fe(II) is released from the protein it could form Fe(OH)2 which can oxidise to a greenish colour – Alan Boyd Aug 10 '14 at 13:54
so you think that is what it is is Iron hydroxide which gets further oxidised? Well than is it the formation of Iron Hydroxide(given that I have a pad on during that time which absorbs the blood) that is really slow or is it the oxidation of Iron Hydroxide that is really slow? – Caters Aug 10 '14 at 14:30

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