peel it off

It should pop right off. Use the corner of a single edge razor blade to do it if your fingernail doesn't work.

Isn't this the contractors problem?

Yes, the contractor should have cleaned up, but this is a 2 second cleanup job.

I would not use a single edge razor blade. This risk is too high, for your hands and sink. It should pop off easily.

I don't think there is any risk to a porcelain sink to have a razor blade slid across the surface at an oblique angle. I've done this many times to clean up a sink that has, for example, paint droplets on it.

the risk is to the operator not the sink. Use a blade with a handle. Single edge razor blades are the largest single cause of laceration injuries in the lab.

Hope it is not 60-40.

If so a HAZ-MAT team will have to be called in after the EPA accesses the situation..

Then congress will have to vote to outlaw pedestal sinks due to the risk of solder drippings.

Beat that one to death!