Prior to cooking, the potato should be scrubbed clean, washed and dried with eyes and surface blemishes removed, and basted with oil (usually olive oil) or butter and/or salt. Pricking the potato with a fork or knife allows steam to escape during the cooking process. Potatoes cooked in a microwave oven without pricking the skin might split open due to built up internal pressure from unvented steam. It takes between one and two hours to bake a large potato in a conventional oven at . Microwaving takes from six to twelve minutes depending on oven power and potato size, but does not generally produce a crisp skin. Some recipes call for use of both a microwave and a conventional oven, with the microwave being used to vent most of the steam prior to the cooking process.