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Prussian blue is a pigment that has been manufactured since 1704, when Heinrich Diesbach discovered it almost by accident in Berlin, which was then located in Prussia. This pigment is incredibly colorfast, and it was the first truly artificially created pigment to reach the market. The deep blue tone and colorfastness rapidly made it immensely popular in Europe and beyond, and it continues to be used today. There are other uses for the pigment as well, ranging from laundry bluing to treatment of people who have been exposed to certain radioactive elements.
Pure Prussian blue is a very deep, rich blue. It can be mixed with other pigments to create different shades, or used on its own. Painters, woodcutters, and textile artists all work with the color, and it was also historically used to manufacture blueprints. Many art supply stores stock it, along with an assortment of related colors, like Chinese blue, which is a blend of Prussian blue and other pigments.
In laundry bluing, Prussian blue was historically added in trace amounts to laundry water to make yellowed whites look more crisp. In microscopy, it is often used as a stain to look for traces of iron, and the chemical properties of the pigment are also utilized in chemistry. Several companies make various versions of that are specifically targeted at these uses; the blue in artists' pigments, for example, has a slightly different formula than the ferric ferrocyanide used in microscopy.
Medical professionals may also prescribe Prussian blue for use in treating people who have been internally exposed to cesium or thallium. Internal exposure can happen through ingestion or inhalation, and it can be quite dangerous when not quickly treated. The pigment binds to these elements, preventing the body from absorbing them and expressing them quickly through the intestines to minimize exposure. Prussian blue should not be taken orally without the direction of a medical professional, as it is very important to calculate an accurate dosage and to take a version which has been specifically designed for this use.
The most common side effect of this treatment is constipation. One of the more intriguing side effects is blue stool, caused by the expression of the pigment from the body. Some patients also end up with blue mouths if the capsules crack open while they take them.