These stamps were issued in 1882-83. They were to be used for foreign mail only. Mexico joined the UPU in 1879 and their postal rates were different that the UPU rates. Therefore, it was decided to issue a new series for the payment of foreign mail only. The initial issue were the Stamps depicting Juarez. Then in 1882 this "small numeral" set of 3 were added. These are interesting for many reasons. They were patterned after the postage due stamps of the United states. They were the last stamps to use the District Name/Number combination on the stamps. They were only allowed to be used on mail going out of Mexico and therefore very few made their way back to Mexico for collectors, making most of them scarce to rare. They are a beautiful example of the philatelic art. (They are found on mostly thin to medium paper. The 6 cents has a wide variety of shades as can be seen in the other listings.) These are all that I have, so once gone they are gone.