How can I tell the difference between a vein and heat discoloration?
This is easy. Heat evaporates the water from the stone. If the dark area is surrounded by a chalky white ring, it is most likely heat discoloration. Another clue is that it is on the inside and not on the outside, where it was exposed to less heat. This is a good reason to never use hotter bulbs than your fixture was designed for. If the dark spot is on the outside or does not have a white chalky ring around it, it is naturally veining.
Heat discoloration is caused by water evaporated from the stone. If a chalky white ring surrounds the dark vein, then the dark vein is most likely a heat discoloration. Another clue is if the mark only occurs inside the light cup because it is closer to the light bulb where the temperature is hotter. Otherwise the dark vein is a natural one. To prevent heat discoloration from happening, always follow the instructions for choosing a fixture.
