I need to know how long blood would be visible on stone.
The situation: I have a culture on my hands whose people are fond of adorning their outer walls with symbolry painted in the blood of sacrificial animals (to gain protection against evil spirits, as you do).
Question: How often would they have to repeat this? Yearly? More often? That is, how quickly would frost, wind, rain, sun etc wash the blood away/bleach it out? Ideally, I would want the repainting to happen yearly, half-, or quarter-yearly.
The stone in question is granite (but I could always change that, since it only registers to the viewpoint character as "grey stone" anyway). The climate we're dealing with is cool, windy, and humid (think Scotland).
- Does the season in which the blood is painted on matter?
- I'm thinking carving the symbols into the stone before putting the blood on might make it visible longer. Correct? How much time does it gain me, approximately?
- What exactly would the dried blood look like? Brown? Dark brown? Black?
- Is the dried blood crumbling/flaking off a problem? How could I solve it? Making it into a sort of paint paste with grease, maybe?
The setting is fantasy, if it matters, but I'd like this to be plausible, and magic is definitely not an option.
Thank you in advance for any and all input!