Rick,
I gonna add my 2¢
Casting with different molds, that is, different block designs as well as different block materials, often require different techniques, much like you have stated in the OP in regards to Alum vs Iron.
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For whatever reason Brass molds need more heat. Some brass molds, not all, can develop tinned spots (boolit alloy sticking to the mold) on the block face, near the cavity. It seems that some designs just create hot spots for this tinning to occur. It's a real pain to remove the tinning and it's important to do so, for casting quality. A good patina will discourage this tinning.
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If you have had a mold, like I have, that has tinned, you will read closely to the discussion about getting a patina built up on the mold. Many casters, who have brass molds, haven't experienced this and likely won't. That is why there is conflicting discussion whether heat cycling, or other patina conditioning is necessary.
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If this mold isn't one of the troublesome designs, then if you just start casting, you will likely have no troubles. But if you have some trouble, you'll get a lesson in tinning removal and tricks to develop a patina.