I bought a Skelly porcelain pipeline sign. It has some kind of stuff around two of the grommets...looks like hard crystallized tar. It is stuck to the porcelain. Some has “flaked” off using my fingernail and great pain!!! Does anyone know how to remove this mess or am I stuck with it (no pun intended). I was afraid to use a metal tool thinking I would damage the porcelain.
Thanks,
Steve

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