Alloy composition

Kilograms of each metal to cast bronze, brass or soft solder, compensating for losses to oxidation and dross.

Alloy

Mass of alloy you want to obtain kg

Losses to oxidation and dross %

Share of the charge that is lost. 2-5 % is usual with good flux and a covered crucible.

Result

Each metal weighs total charge × its percentage ÷ 100, with total charge = final mass ÷ (1 − losses ÷ 100).

Example: 10 kg of 90/10 bronze with 5 % losses. Charge = 10 ÷ 0.95 = 10.53 kg; copper = 10.53 × 0.90 = 9.47 kg; tin = 10.53 × 0.10 = 1.05 kg.

Example: 4 kg of an alloy with 15 % second metal and 2 % losses. Charge = 4 ÷ 0.98 = 4.08 kg; second metal = 0.61 kg; base metal = 3.47 kg.

Moisture: water in contact with molten metal turns to steam instantly and throws metal out. Preheat crucibles, tools, ingots and scrap before putting them in the melt; moulds must be thoroughly dry. Never over damp concrete floors.
Protection: leather boots, spats, leather apron and gloves, face shield; no synthetic fibres, which melt and stick to the skin.
Melting points of the pure metals: tin 232 °C, lead 327 °C, zinc 420 °C (boils at 907 °C), copper 1085 °C.
Approximate melting ranges (liquidus): 90/10 bronze ≈ 1000 °C; 78/22 bell bronze ≈ 870 °C; 70/30 brass ≈ 955 °C; 60/40 brass ≈ 905 °C; 60/40 solder ≈ 183-190 °C; 99.3/0.7 tin-copper 227 °C. Pour at about 100-150 °C above the liquidus.
Charging order: melt the metal with the highest melting point (copper) first and add the lower one (tin or zinc) at the end, preheated, to reduce losses. Zinc is lost more than copper: for brass 1-3 % more zinc than calculated is usually added.
Proportions are by mass, not volume. Bronze or brass scrap is already an alloy of unknown composition: melt it separately or analyse it before mixing it with pure metal.
Sources: melting points of the elements from the CRC Handbook of Chemistry and Physics; alloy ranges from Copper Development Association data sheets and the ISO 9453 solder standard (approximate values).