Cloudy Glasses: Mineral Film or Permanent Etching?

The test

Fill a bowl with white vinegar and submerge one cloudy glass for fifteen minutes, then rinse and dry it. Compare it with an untreated glass side by side in good light.

A clear glass means mineral film — calcium and magnesium deposited from hard water, sitting on top of the surface. A still-cloudy glass means etching, where the glass surface itself has been chemically dissolved into a microscopically rough finish that scatters light.

If it is mineral film

This is the good outcome: it is reversible and preventable. Fill the rinse aid reservoir and turn the dosage up. Descale the machine with a food-safe product, and set the interval by your water hardness — quarterly at 7 to 10 grains per gallon, every six to eight weeks above that.

If your machine has a salt reservoir, fill it and set the hardness dial correctly. Rinse existing glasses in vinegar to restore them.

If it is etching

Etching is permanent — no product, service or cycle will reverse it, and anyone who tells you otherwise is selling something. What you can do is stop it happening to the rest of your glassware.

It is caused by the combination of soft water, excess detergent alkalinity and high heat. Soft water is the key ingredient, which is why households that install a softener often see etching appear for the first time.

• Cut the detergent dose, often by half in soft water.
• Use a lower-temperature cycle for glassware.
• Turn off heated dry, or use a shorter drying phase.
• Skip pre-rinsing so the detergent has soil to act on rather than attacking the glass.
• Hand-wash thin, delicate or antique glassware.

The confusing middle case

Some households have both: hard water depositing film on top of glasses that were etched years ago in a previous home or a previous machine. The vinegar test on several glasses of different ages usually reveals this — some clear up, some do not.

In that case treat the machine for hardness and retire the etched glasses; keeping them in rotation makes it impossible to tell whether your maintenance is working.