Chromium Corporation has supplied foils to organizations in the United States and 20 other countries. Specialty foils outside these types can be made. Type B foils are selected to have a central area through which no light can be seen when the foil is strongly illuminated from the rear. The foil is normally square, and the central area has a diameter of magnitude at least half the length of an edge. Type C foil is selected to be light-tight over its entire area.
Type D is very thin nickel foil with a copper backing, without warranty as to porosity.
Normally, the user will dissolve the copper in a special solution before beginning studies. Conventional foils are made by rolling mill reduction of a small billet down to a thinness of foil dimension. The research grades of foil made by Chromium Corporation are produced by electroforming a web that is started at zero thickness and grown to foil dimension. Through this approach, ultra thin foils are attainable. Some incipient weights are membranes with perceptible tensile strength so low that a copper support is required until they may be mounted upon utility apparatus.