eschar

A superficial structure of dead tissue, usually hardened, and commonly but not necessarily dark, adhering to underlying living or necrotic tissue, caused by gangrene or a burn.

...stable intact eschar on the heels should not be removed. Blood flow in the tissue under the eschar is poor and the wound is susceptible to infection. The eschar acts as a natural barrier to infection by keeping the bacteria from entering the wound. If the eschar becomes unstable (wet, draining, loose, boggy, edematous, red) it should be debrided according to the clinic or facility protocol

Any hard, dark, commonly flattened or sunken lesion or crust, especially on a burn, abscess, infection, wound; commonly a coagulation of blood or exudations, not necessarily involving dead or necrotic tissue.

When the caustic is removed, the eschar should be punctured for the discharge of the matter, and then dressed with warm emollient poultices...

The emotional imprint of a trauma such as grief, loss, or degradation.

In another minute there was no letter; but, as with every other relationship in my life, an eschar of ashes. The word is rare, but exact.