Copper Alloys....Brass and Bronze

Brass is an interesting metal, and is as easy as aluminium to cast except that you need to get it hotter.
Understatement of the year, but true, it will produce a degree of zinc fume when melting and of course when molten, and it is unadvisable to hold the metal molten, as zinc will be lost through oxidisation.
I have found that the best way to lower the fuming and retain the zinc is to cover the melt with a layer of BORAX BP I use borax BP. as obtained from a chemist, but any form of borax will work providing there are not additives present.
The borax forms a type of glass that floats on the brass and effectively forms an airtight seal against atmospheric contamination and oxidisation. Depending on what type of metal you start with generally depends on what is left after melting and poring, but I have found that if a good quality "TAP" brass is used, as found in household water taps (Remove the chrome with solution of hydrochloric acid first)
Then the resultant metal will be a little softer and easier to cut, you can add a little lead or plumbers solder to the melt to increase the machinability, but be very careful that you do not add too much, as can cause flaking / cracking of the brass with deposits of lead oxide inside the cavities, but just enough can produce a wonderful machining metal. Some experimentation is required along with careful note taking and weighing of the additives.

The Table below is as good a reference as to what brass can be found in various products and will provide valuable guide as to the type of metal.