This "Single Groove" or "Cross Top" has some strange glaze. The grayish brown mix surfaced only on one side and in the top grooves. The picture shows rust in the groove, after cleaning it, it's the speckled gray color. I know very little about porcelain... my questions: 1. What caused the strange glazing? 2. Why only on part of the insulator? The darker areas look like granite rock. The insulator is coated smooth any shiny every where except the chipped spots. How about it, can you porcelain experts enlighten us? Thanks for any answers.