I was trying to cast some brass for a brass letter opener I was making as a Christmas gift, but it all failed. I cast it with only a minor failure the first time (brass was full of slag inclusions or something and it was full of cracks) I read on some other forum that borax could be used to help prevent oxidation (kind of like how glass is used when casting iron) I loaded a stainless steel crucible (home made) with the last of my brass and a touch of aluminum (I was worried I would that too much material would burn off and someone said that brass/bronze with aluminum cracked less often when forging). I placed the crucible in my homemade propane forge (It just about barely can heat up enough to melt brass, I cant even melt copper or silver) but when I tried to cast it Only a small amount of liquid came out the rest was some black substance (like iron filings and charcoal powder mixed with flecks of some shiny metal). The cast material was a clear mixture of some reddish/rose colored material, and some whiter stuff (Possibly aluminum and some other metal) the crucible crap upon further inspection looked like it contained 3-4 different metals or something in it mixed thoroughly with that black substance. I’m still a novice even at iron working, so I don’t even know what happened here, my best guess is that the borax is the black stuff and it’s separating the individual pieces of scrap I tried to melt together? I also noted there was a little metal with the original brass color a reddish one and a faintly pink/whitish one. Is it possible the zinc separated from the copper in the crucible? (it’d explain why I see different metals at all in the crucible trash). (Oh and the original brass came from a decorative drawer piece, a cut up propane nozzle, and a small amount of some other brass scrap). I’m on my last piece of brass, but I don’t want to touch it till I know what the heck happened today, if someone could help that’d be nice.
use naval bronze(brass) or silicon bronze. the “bronze” decorative piece was probably pot metal with a bronze finish. To cast bronze it needs to be around 1800-2000 deg depending on the thickness and complexity of the final piece. I owned a bronze foundry for many years and never used aluminum. aluminum melts at around 1200 deg and burns around 6920 deg (thats why they use it in some solid rocket fuels) it then produces alumina. the brass you were using was probably poor grade having been cast from various scrap brass/bronze before you acquired it . A lot of statue/ art work you see for sale that is cast in India, Pakistan, China is cast from scrap and does not take a patina evenly or at all sometimes. Also if you get the bronze too hot it will start absorbing gases and creating gas bubbles which will make it crack an have a porous granular texture that with break easily when you try to work it. try using a graphite or clay crucible Not stainless. that also probably contributed to your problem. I have graphite crucibles that are over thirty years old and are still in good condition. also remember you have to scrape the slag off the top of the molten metal before you pour it or all of the impurities that have floated to the top(including the flux) will be reintroduced into the metal and create inclusions, air pockets, and just a big old mess. also what are you pouring the metal into greensand or ceramic shell? each has its own issues. I used ceramic shell casting as I could do compound curves and create life size statues far cheaper/safer and easier to use.(still a health issue though that must be done in a controlled environment with negative air pressure in the shellroom and special filters on masks) green sand is bulky, extremely fragile and you cant get the detail as with ceramic shell casting(you can get as finger prints).