In 1898, a Krefeld, Germany, company introduced woven silk postcards, an idea that combined the concepts of printed postcards and popular woven silk pictures called Stevengraphs. To make postcards, the small woven silk images would be glued to a piece of cardstock. During World War I, such cards most often portrayed the devastation of the war on famous buildings like the Louvain cathedral or portraits of war heroes like British nurse Edith Cavell. Embroidered silk postcards—made of beautiful, ornate images sewn onto a rectangular piece of silk and then framed in embossed paper—debuted in 1900 at the Paris Exposition. They were made up to around 1956. During World War I, British soldiers missing their loved ones were drawn to these fragile and pricey gifts, which they usually sent home in envelopes with letters. The favored embroidered designs ranged from patriotic images of flags or regiment cap badges to romantic depictions of butterflies, birds, rainbows, or flowers like forget-me-nots. Some of these cards had a "silk pocket" effect, which would hold a small pre-printed card. It is believed the embroidery of these cards was done at home by civilian women in France and Belgium, and by Belgian refugees in the United Kingdom. A worker would embroider the same design over and over again into a roll of silk or a strip of silk mesh, which would be sent to a factory in a city like Paris to be cut up and assembled into postcards. The embroidered silk postcards had a brief resurgence around 1939-'40, when members of the British Expeditionary Force began to send them home. The later cards usually have more subdued colors and "crimpled cut" edges. Bits of silk ribbon have also been used as embellishments for posh sentimental postcards like Valentines. Collectors should take great care with silk postcards, as silk is a delicate material, sensitive to light, humidity, and handling. The card stock used for the paper frame during World War I was usually low-quality, so cards from that era often have brown staining known as "foxing."