Glass

Nonporous surface that makes dew-point conditions and seal failures visible.

What changes first

Look for surface droplets, edge fogging and internal haze. The pattern and location usually matter more than color alone.

Moisture and movement behavior

Record whether the material changes after rain, water use, heating cycles or seasonal humidity. A material can display the damage while the source is somewhere else.

Before repair

Determine whether the material is the source, a pathway or only the final surface. Correct the controlling condition before replacing finishes.