Brand new. First use. Put in one of the wrapped paper log pulled things. Sat and watched it burn beautifully. And then the black tar like substance filled the glass door. Because it's for open fires not log buners. And I didn't see that until ooh, about 3 hours in. I've tried water, white spirits, ceramic hob cleaner, ethanol, maths and nothing is shifting it. I've wrecked it haven't I??