“Temperatures can be raised with energy released during exothermic... reactions. Copper and {{w|lead}} are commonly located in close proximity... A mixture of ...{{w|malechite}} ...and ...{{w|galena}} ...heated to only to 700 °C ...automatically reaches a temperature, through a heat producing chemical reaction, that is close to that for extracting copper. The addition of a flux, which in Egypt was a native salt called {{w|natron}} ({{w|sodium carbonate}}), lowered the fusion point sufficiently for copper extraction. Silver can be smelted similarly.”