Bordeaux mix is a mixture of Copper Sulphate (CuSO4) and Hydrated Lime (Ca(OH)2, Calcium Hydroxide) it was used as an agricultural antifungal and antibacterial agent.
Originally used in 1885 in Bordeaux, France for the prevention of Black Rot on grapes and leaf spot and apple scab on fruit trees. Used as both a spray in the orchard and as a seed treatment. Its widespread usage continued until the early 1930's.
Its use was discontinued when it was noticed that it caused the russetting of fruit, and damaged the leaves leading to premature defoliation. It was replaced by Burgundy mix which substitutes Sodium Carbonate (Na2CO3) for the Calcium Hydroxide. Burgundy mix has now largely been replaced with more convenient sprays and treatments.
The rise in the popularity of organically produced fruit and vegetables has spawned a new interest in both the Bordeaux and Burgundy mixes, and they are commercially available as prepared sprays under a variety of brand names for use both domestically and commercially.