Blistered Black Oak Leaf

Have you ever wondered what happens to a green leaf that is exposed to extreme heat but isn't burned? You are looking at a leaf that had been green. Fire approached but only the extreme heat hit these leaves, causing the water within to boil and create the blistering of the surface. Although this leaf did not burn, it turned black and was dry as a bone. These leaves look to me as if they are cast from bronze.