An early nineteenth century Berlin Iron signet ring, engraved with a 'P', the shank finely decorated with a further foliate motif, size 12, 12.9 grams, circa 1830. 

Though known for use in jewelry production dating back to the Roman Era, cast iron jewelry came to prominence in the early part of the nineteenth century through an odd confluence of circumstances. At the turn of the century, elaborate ballgowns with large crinolines fell out of fashion and were replaced with sheath-like dresses, featuring empire waists and tiny puffed sleeves (think, Bridgerton), with women emulating Grecian goddesses. As opposed to the opulent diamond and gemstone jewelry that bedecked necklines in Paris, fashion in Prussia favored classical simplicity. Furthermore, the royal house of Prussia endorsed a lifestyle of relative modesty compared to the sumptuousness of other royal courts. Thus, cast iron jewelry became an emblem of modesty and intellectualism in Prussia. The final element, patriotism, fell into place during the Wars of Liberation (1813-1815) against Napoleon, when cash-strapped Prussia asked its citizens to donate gold jewelry in exchange for cast iron jewelry to fund the ongoing war effort thus giving rise to the inscription 'Gold gab ich fur Eisen' ('I gave gold for iron'). After the defeat of Napoleon, cast iron jewelry continued in popularity taking on new gothic and naturalistic forms until its appeal faded in the latter half of the nineteenth century.