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efreysson
05-29-2017, 03:04 AM
I have characters finding a sacrificial altar on which a LOT of blood has been spilt, in a cave system way, way beneath the earth. The air is dry, and the cave has been abandoned for a thousand years. Would the blood still be visible, or does it fade over time even in those kinds of circumstances?

Cyia
05-29-2017, 03:28 AM
Blood degrades. There *might* be stains on the stones, but the blood would be gone.

efreysson
05-29-2017, 01:39 PM
Blood degrades. There *might* be stains on the stones, but the blood would be gone.

What would those stains look like?

Cyia
05-29-2017, 07:06 PM
They'd be dark brownish splotches. If enough blood was present the entire surface could be turned dark brown on top, with only the surrounding area showing the true color. With stone, it would likely look like the rusty color is the natural hue until compared to what's around it.

Marlys
05-29-2017, 08:04 PM
You might find this interesting--blood residue found on 2000-year-old knife. (https://phys.org/news/2012-05-mexican-experts-ancient-blood-stone.html)

Cyia
05-29-2017, 08:09 PM
The knives are obsidian, so smoother, like glass. Coarse stone is different. (But the fact that they were able to isolate actual red blood cells is phenomenal!)

MaeZe
05-29-2017, 10:41 PM
You might find this interesting--blood residue found on 2000-year-old knife. (https://phys.org/news/2012-05-mexican-experts-ancient-blood-stone.html)

Ignoring the fact this is the Daily Mail, they have pictures: The blood and hair that proves Mexicans used stone knives for human sacrifice 1,000 years before Aztecs (http://www.dailymail.co.uk/sciencetech/article-2138946/The-2000-year-old-bloody-knife-PROVES-ancient-Mexicans-practiced-human-sacrifice.html)

It took an electron microscope to identify the tissues suggesting the blood wouldn't be visible. Not that your link isn't fascinating anyway.

Red blood cells are heavy in iron, stains would likely look like rust. If one wanted a story element, one could note the rusty look of the alter differs from the surrounding stone, then note, 'iron!' for the eureka moment. :D

Tsu Dho Nimh
05-30-2017, 02:30 AM
Dry or not, cave critters and bacteria would degrade the blood a lot.

Iron stains - brown splotches - is about what you would find.