If perchance you would like to make your own starch instead of buying pure starch or just ironing the wrinkly article, here is a recipe for making starch from frosted potatoes, with the language modernized from the 1881 Household Cyclopedia:

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Nearly frozen ("frosted") potatoes can be used to make a good, but impure (slightly dark) starch that can be used to starch dark-colored clothes. It should not be used on light-colored clothes, such as dress shirt collars or nuns' wimples.

1. Grate the frozen potatoes into water.
2. Remove the solids by hand and retain for additional extraction.
3. Strain the liquid through cheesecloth or a fine sieve.
4. Continue extracting the potato solids by stirring in water and allowing the solid material to settle, then decanting the liquid through cheesecloth or a sieve as before, until the wash water is clear.

Note: you really should use unfrozen potatoes, since they yield about twice as much starch as frozen potatoes. But if all your potatoes have become frozen, you may extract starch from them anyway.

The remaining potato solids can be used to clean wool clothes without affecting their color, and the water filtered from the starch powder is excellent for cleaning silks without affecting their color.

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This all of course begs the question of why you would want to know how to make starch from frosted potatoes. Perhaps the information will be useful for someone writing an historical novel about 19th-century nuns caught in a snowstorm?