The first thing you have to do is to experiment with each of the colours you use. Some colours produce a stronger pattern e.g. blues usually give a better result than yellow. If your silk dries too quickly the dragging effect of the colour may stop before the salt has finished dragging the colours….this could be an effect you want and you may decide to dry the silk more quickly by using a heater (hair dryer). Also you can experiment using fine table salt and larger granules of rock salt.