The earliest form coatings were unmodified oils of mineral, vegetable or fish origin. This kind of oil, still in use, contains no added surface-activating agents. Straight oil or mixture of oils to which up to two percent surfactant has been added will produce concrete surfaces reasonably free from bugholes and color differences. In water-in-oil emulsions, oil is the continuous phase in which water globules have been dispersed by means of an emulsifier. The kind of emulsifier and the amount used are critical because the emulsifier often causes color differences on the concrete surface. Nonuniform distribution of the emulsifier in the emulsion will also affect the color of the concrete surface. Waxes, usually carnauba wax, which are used as release agents have excellent release characteristics. However, application is limited to use at air and from temperatures above 50 degrees F. Regular wax is difficult to apply uniformly, a factor which may increase labor costs. However, emulsified waxes that can be brushed or rolled on the form have substantially reduced this difficulty. Volatile coatings, another of the group of products based on petroleum, utilize a light paraffin or naphthionic crude base as the vehicle, which also contains various other ingredients. Chemically active release agents contain compounds that react with the free lime present in fresh concrete to produce water-insoluble soaps and prevent the set of the film of concrete in contact with the form.