What is the black material on the wood that looks like a glue or caulk?

Some customers have asked if this is caulk, glue or even black ink. The black material is caulk from the glass unit. The glass units are overpacked with the black caulk sealant for optimal sealing. This can ooze out slightly, but is easily removed. We would not consider this a defect either structurally or cosmetically.