Victorian Trade Cards can be quite valuable, depending on the theme and if in fine to near mint condition. Companies in the late 1870's to early 1900's distributed trade cards as promotions with products and almost any consumer item of that era can be found advertised on a card.
Of particular interest to trivet collectors would be those cards advertising laundry day products such as sadirons, stoves, and laundry soaps. The front of the cards were usually decorative, humorous, or offered some sort of political commentary; the backs were reserved for company advertising.
People of that era collected the cards, gluing them into albums along with calling cards and other mementos. Collectors today prize these albums, as the valuable trade cards can be carefully soaked from the album pages and pressed, dried, and redistributed for sale. Most cards were made of a combination of paper pulp and rag, similar in composition to paper money, and have proven extremely durable.
Interested in learning more? Search for a copy of Dave Cheadle's book Victorian Trade Cards (Collector Books, 1996).