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Tried casting for the first time

Well I have just tried casting for the first time. I cast 2 rings
seperately and they did come out. But I have a couple of questions:

  1. the castings both had a black scale on them. The first time I
    poured I didn’t hit the hole in the casting directly and it seemed
    to smear the black over the investment and only a small amount
    appeared on the sprue of the casting. Obviously my aim was better the
    second time and the black ended up on the casting. What did I do
    wrong. I added a pinch of flux before I started the automatic furnace
    and added a pinch at liquidus.

  2. how do I clean out the graphite crucible? I’m thinking a wire
    brush would not be a good choice, but I don’t know.

Note: I used a vacuum caster, programable burnout over, and an
automatic melting furnace. I used Kerr’s burnout cycle
recommendation and the casting and flask tempurature recomendation
from the refiner for the gold alloy I used.