unyquity
....directly to your skin? All the links that I've ever posted for using an activated charcoal poultice include instructions to mix the charcoal & "other" together and put it on a cloth or paper towel, cover it with plastic wrap, and then apply it (cloth side down) to 'whatever'.
I honestly have no idea if it will 'tattoo' a sunburn - hopefully the skin damage is shallow enough the the 'black' will just peel off or abrade away. I sure hope so! If you skin isn't dark/black now, it won't turn black.
Charcoal adsorbs toxins - I've never heard of it being beneficial for sunburn. Aloe is your best bet for sunburn - aloe & slippery elm would be fantastic. Likely the best would be Dr. Christopher's Burn paste...a mixture of raw honey, (powdered) comfrey roots/leaves/flowers (works much like aloe, with allantoin as the cell regenerator) and wheat germ oil.
Speaking of which, I've gotta get some of that Burn Paste mixed up and stored in the 'fridge for emergencies soon.
Blessings of the non-tattooing kind!
Unyquity