Living · 6 pages · 12 min
How hard water spots a glass
When the drop dries, dissolved calcium and magnesium stay behind as a spot.
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From the opening
Hard water spots a glass because the water carries dissolved calcium and magnesium, and those minerals stay when the water evaporates. The pale dot is rock left on the surface, not a smear of leftover food. The opening covers calcium and magnesium dissolved in the drop, evaporation leaving the minerals, and heat pushing scale out of solution.
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Inside
- Calcium and magnesium dissolved in the drop
- Evaporation leaving the minerals
- Heat pushing scale out of solution
- Etch versus a wipeable deposit
- Where the idea stops applying
- A distinction worth keeping
Sources
- Calcium and magnesium hardness in tap water
- Carbonate scale left by evaporating hard water