created using natural ice. At the start of the twentieth century it had been described as "one of the finest covered rinks in the world" and was used during winter for pleasure skating, ice hockey, and skating sports. In summer months, the building was used for various other events. Types Natural ice Many ice rinks consist of, or are found on, open bodies of water such as lakes, ponds, canals, and sometimes rivers; these can be used only in the winter in climates where the surface freezes thickly enough to support human weight. Rinks can also be made in cold climates by enclosing a level area of ground, filling it with water, and letting it freeze. Snow may be packed to use as a containment material. An example of this type of "rink", which is a body of water converted into a skating trail during winter, is the Rideau Canal Skateway in Ottawa, Ontario. Artificial ice In any climate, an arena ice surface can be installed in a properly built space. This consists of a bed of sand or occasionally a slab of concrete, through (or on top of) which pipes run. The pipes carry a chilled fluid (usually either a salt brine or water with antifreeze, or in the case of smaller rinks, refrigerant) which can lower the temperature of the slab so that water placed atop will freeze. This method is known as 'artificial ice' to differentiate from ice rinks made by simply freezing water in a cold climate, indoors or outdoors, although both types are of frozen water. A more proper technical term is 'mechanically frozen' ice. An example of this type of rink is the outdoor rink at Rockefeller Center in New York. Construction Modern rinks have a specific procedure for preparing the surface. With the pipes cold, a thin layer of water is sprayed on the sand or concrete to seal and level it (or in the case of concrete, to keep it from being marked). This thin layer is painted white or pale blue for better contrast; markings necessary for hockey or curling are also placed, along with logos or other decorations. Another thin layer of water is sprayed on top of this. The ice is built up to a thickness of . Synthetic Synthetic rinks are constructed from a solid polymer material designed for skating using normal metal-bladed ice skates. High density polyethelene