White dew is an ice deposition, sometimes confounded with hoar frost, which formes from dew that has frozen, especially during cold, clear nights. Unlike hoar frost, it does not forms directly from water vapour. It doesn't need to be frost (i.e. a temperature of the air below the freezing point) to form white dew: the only condition is that the surface with dew will reach a temperature of 0 °C. White dew can be distinguished by hoar frost by noticing dew drops transformed into small ice balls.