How much would it be worth? In spiritual or material currency.
Do you mean your own blood or someone else’s? I personally would not ever pay for someone else’s blood on a piece of paper. In fact you’d have to pay me a significant amount to convince me to take such an item. Unless it was someone I wanted to curse, but I am not much one for that.
I can’t speak to “spiritual currency”. If it’s your own blood then by all means keep the paper handy and use it when necessary.
Yep, my own
Nothing without the intention behind it. You can add intention when you’re ready. The blood is long dead and is less valuable than fresh or when accompanied by the emotional energy of the blood letting.
This could be similar to when you make an elixir, which you use for magickal workings without knowing in advance what it will be used for exactly.