Allie:: Those are earthenware pots with a low fire glaze. The sheen is most likely a glaze ingredient that was transferred as fumes during the fireing process.
Treat them as you would any other glazed pot.
Lynn is right, if they were made in China they should never be used for food but as they are unglazed inside they wouldnt be easy to clean.
The Chinese and many other countries who import less expensive ceramics use the cheapest materials and glazes are fired at a low temp.to save money.
Lead is sometimes used as a flux to make glaze turn to glass at a lower temp. therefore as Lynn said, dont use these pots for food storage especially any thing with high acid content like citrus ,tomatoes or Pineapple.
They are beauties and the price was right most definitely.
