Why glasses tarnish in the dishwasher

If you own a dishwasher, then you surely know the problem that your glasses become milky and tarnish after a certain time. In this article, we want to get to the bottom of the causes and answer the questions of how you can avoid glasses tarnishing and how the tarnished glasses can become beautiful again.

Why do glasses tarnish in the dishwasher?

Glass tarnishing is called glass corrosion or glass rust. It refers to the structural change and associated weathering of the surface of glass due to various chemical and physical influences. I.e. as a result of a microscopically thin roughening, due to the release of ions of elements such as sodium, potassium or barium from the glass surface, the glass becomes cloudy.

If your glasses tarnish, this can have various causes, sometimes it is also several factors that coincide in an unfavorable way. Thus comes into consideration:

Influence of the acting substance

This refers to water, washing-up liquid and all other substances with which the glass comes into contact.

  • Too soft water can be a reason for tarnishing of your glasses. To prevent lime deposits on dishes and in the appliance, the water in the dishwasher is usually still softened. However, if you live in a region where the water is already very soft or if you have set the hardness range on your dishwasher incorrectly, the hardness of the dishwashing water may drop below 5 °dH. In this case, the soft, very aggressive, water can damage your glasses if it comes into contact with them for a long time.
  • If the water temperature is set too high and there are strong temperature fluctuations, the glasses will be stressed and thus increase the aggressive effect of the soft water.
  • During the drying process, the acting water vapor can damage the glasses.

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Influence of glass composition

Glass corrosion in the dishwasher may also depend on the quality of the glass material used. Especially cheap glasses and glasses made of inferior quality glass run milky faster than good and high quality glasses. However, it can also happen that expensive glasses tarnish after many wash cycles in the machine. This is of course annoying.

This microscopic roughening is often also caused by purely mechanical effects, such as rubbing the glasses together or contact with parts of the dishwasher under £300.

Note: As a rule, your glasses will not spontaneously tarnish during a single rinse cycle. This usually happens only after some time and after many rinses. You will also not find the clouding distributed over the entire glass, but mainly in heavily used areas.

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How to avoid tarnishing of your glasses?

Is there a cure-all for glass corrosion? Glass always suffers from the chemical additives in dishwasher tabs or powders. In addition, you usually don’t know anything about the glass composition when you buy it. However, you should consider the following points to avoid glass tarnishing:

  • First, you should only ever put glasses in the dishwasher that the manufacturer has labeled as “dishwasher safe.”
  • Carefully sort the glasses into the dishwasher so that they do not touch each other. Resulting scratches can be the first points of attack for glass corrosion.
  • If your glasses tarnish very quickly, check the hardness of the water. Many dishwashers can be adjusted for the lime content of the water. The range should be between 5 and 7°dH. You can find out more about the water hardness in your region from your local water company. If the water is softer than expected, you may also be adding too much dishwasher salt and rinse aid to the dishwasher.
  • Dose the dishwashing detergent according to the manufacturer’s instructions. If you frequently underdose, you risk glass corrosion.
  • Some manufacturers offer dishwashing detergents with special glass protection to prevent damage to the glass. Although this glass protection only has a delaying effect, it does prevent ion migration.
  • With dishwashers, too hot is not always good. Glasses react to too high rinsing temperatures and then tarnish. So it is better to wash the glasses at low temperatures.
  • It can also help if you leave out the rinse aid. Simply too much chemistry is not always good for glass. Chemicals strongly attack the protective layer of glasses.
  • If there is a high dirt load in the dishwasher, you can also pre-rinse.
  • After rinsing, you should open the machine door immediately so that the water vapor can escape, otherwise it can damage the surface of the glasses. It is best to remove the glasses from the dishwasher as soon as possible and not leave them in it for a longer time.

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What to do when glass is already tarnished?

Basically, damage to the glass surface caused by glass corrosion is irreparable. It is therefore not really possible to remove the cloudiness that has arisen.

Especially with cheap glasses of inferior quality, the only option is often to dispose of them. If you still do not want to give up, you can try tips from the Internet. Here are 2 examples:

  1. Put the glasses in a bowl of vinegar water and rinse them by hand. According to some users, this works and the glasses become clear again.
  2. You can also put a bowl of vinegar water in the dishwasher under £400, then put the tarnished glasses in and run them through the dishwasher without adding anything else. Your glasses may well come out clear again.

In the end, these are just some tips to help you with the problem. Otherwise, the only thing that will help is to try it out when your beautiful glasses start to tarnish.

David Shaw

David Shaw

Dishwashers expert with over 10 years of experience. He writes articles and shares his knowledge on many sites. Helps you choose the best (portable, countertop, built-in) dishwashers on this site.

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