It is required to colour the concrete bottom of a sea-water swimming bath so that the bottom can be plainly seen by the swimmer. A Portland cement known as " white cement " might be light enough in colour for the finishing coat without any further mixture. Or limestone chippiugs, pulverised very finely, may be mixed in the finishing coat, and a skin can be made in this way which is almost milk white. White enamelle 1 bricks would make a much better job, but expense may prevent their use. In any case, occasional strips of colour, running along the length of the bath, should be formed in the bottom by colouring the cement with Venetian red or red ochre. This colouring is useful as a guide to swimmers when swimming under water.