Many typewriters offer you the choice of ink colour (usually black and red). The ribbon is half each colour and a setting on the typewriter lets you select which one to use, the ribbon will be raised the correct height so the desired colour will be put between the type head and the paper. However, typewriters will often also have a third "colour" option, which looks white or clear. This doesn't raise the ribbon at all.
So, what is this for? Invisible typing? An ink saving measure? In fact this is stencil mode, to facilitate an early mass copying method. In stencil mode the type heads make holes in a special sheet of paper for use with a mimeograph or ditto. Once the master copy has been typed then dozens or hundreds of copies can be created. This is how schools, for example, were able to run off hundreds of copies of letters in the days before photocopiers and laser printers.
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| Selector on a Litton Imperial 201, top option is stencil mode |
