Place the scrap or bullion brass in a smelting or casting crucible. If one is not available, you can make one with a ceramic mold-making kit and two large, deep glass bowls. Pour the liquid casting rubber into a glass bowl and press an identical bowl, with its exterior sprayed with a molding release agent, into the rubber until it overflows. Place a light weight on top of the inner bowl and allow it to set for four hours. Remove the inner bowl and fill the rubber cavity with a ceramic/activator paste, forming it up the sides to create an inch-thick vessel.
Allow the vessel to set for 24 hours. Cover the vessel with a ceramic plate or china dish and cure it at 2,600 degrees Fahrenheit in a kiln. If no kiln is available, place the vessel inside a circular stack of firebricks on end and pack charcoal around and over the covered vessel and burn it for two hours.
Fill the crucible with scrap metal or brass billets, cover the crucible and place it in a forge. If a forge is not available, construct one from a lawnmower shroud and concrete. Screw a right-angle fitting onto a 3-inch length of 2-inch steel pipe and screw a 3-foot piece of 2-inch steel pipe onto its other end. Weld the short pipe end of the 3-foot steel pipe assembly into the bottom center of the shroud.
Fill the inverted shroud with a 50/50 cement/perlite mixture of concrete three inches thick. Hand-form more concrete six inches above the sides of the shroud, forming an interior forge space 18 inches in diameter. Allow the concrete to cure for 24 hours.
Use duct tape to connect a high-volume hair dryer to the end of a six-foot length of shop-vac hose. Tape the other end of the hose to the outside end of the right-angle, 2-inch steel pipe.
Place the metal-filled crucible inside the forge and cover it and the surrounding area with hardwood charcoal ten inches deep. Spray the charcoal with kerosene or lighter fluid. Turn on the hair dryer and light the forge. Allow the forge to burn for 90 minutes after it reaches a cherry red color.
Turn off or disconnect the hair dryer. Scrape any charcoal or ash from the crucible cover. Clear the charcoal and ash from around the crucible. Use casting tongs or forge calipers to lift the crucible from the forge and place it on a flat concrete surface. Remove the crucible lid and pour the brass into ingot or casting molds.