Second degree burns occur when the first layer of skin is burned through and the second layer, the dermal layer, is damaged but the burn does not pass through to underlying tissues. The skin appears moist and there will be deep intense pain, reddening, blisters and a mottled appearance to the skin. Second degree burns are considered minor if they involve less than 15 percent of the body surface in adults and less than 10 percent in children. When treated with reasonable care, second degree burns will heal themselves and produce very little scarring. Healing is usually complete within three weeks.
Third degree burns involve all the layers of the skin. They are referred to as full thickness burns and are the most serious of all burns. These are usually charred black and include areas that are dry and white. While a third-degree burn may be very painful, some patients feel little or no pain because the nerve endings have been destroyed. This type of burn may require skin grafting. As third degree burns heal, dense scars form.
BTW, I never saw blisters turning black before... it was quite alarming. Oh, and after I removed the top blackened skin, there was no bleeding or anything, just brownish residue I believe to be skin cells.