Black spots on cups from Cracker Barrel

I have a favorite cup made in China that has developed black spots inside the bottom. I'm worried about lead -- should I stop using it? It isn't crazing but seems to be a failed glaze. I bought 6 of these from Cracker Barrel restaurant a year ago as part of a set with serving dishes signed by Susan Winget -- the Nature Walk series for Cracker Barrel Old Country Store. The add picture function isn't working but I can send pictures to anyone who's interested.
Best Answer
You can buy lead testing kits online or a hardware store. (You want test swabs, not a water-testing kit). Expect to pay $10–20.
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