How bordeaux mixture is prepared?

A quantity of 400 g of copper sulphate should be dissolved in 20 litres of water, and 400 g of lime should be dissolved in another 20 litres of water. By constantly stirring the mixture, the copper sulphate solution should be added to the lime solution. Metallic containers should not be used, and only earthen or wooden vessels and plastic containers should be utilised. A polished knife should be dipped in the mixture for one minute and then removed to see if the proportions are proper. If there is a reddish brown copper deposit in the knife, more lime should be added until there is no deposit.