Brass Casting, Poor Surface Finish

[NedsHead]

I made a small spherical graphite mold today for my brass casting but the surface finish still isn't great, are there any tricks to getting good surface finish with brass? maybe I need to preheat the mold..?

Here's some pics of the process and the cutter I knocked together, it's just a washer with a sharpened edge fixed to a shank, actually worked really well and gave a nice finish.
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This one was a fail, some flux was still in the melt and went into the mold
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Here's my second try, not bad but a poor surface finish
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[Nrcollar]

Heads
I believe you would do a better job with a metal mold then preheat while metal is melting and hold the mold open so it can get a little carbon on the inside of the mold. Hot mold and hot metal should solve the problem.
Nelson