Theceramic sink cleaning?

Fill a spray bottle with a 50/50 solution of Dawn dish soap and vinegar. Spray it on the hard water stains and let it work. If they are tougher stains, you may have to scrub with a plastic scrubber!

Here's another method:

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Wipe the sink with a microfiber cloth but do not wet it first, as a combination of dust and water results in a thick, sludge-like substance. Set this cloth aside to clean it later.

Combine ¼ cup of baking soda and 2 tablespoons of mild dish soap in a small bowl. Mix thoroughly. Add a few drops of white vinegar and stir until the substance is creamy. Drop a few tablespoons of baking soda down the drain.

Dip a sponge into the baking soda mixture and spread it around the sink, rubbing gently. Let the mixture sit in the sink for a few minutes.

Rinse the sink with cool water, removing all traces of the baking soda mixture with the sponge. The water that goes down the drain will mix with the baking soda to keep your sink smelling clean as an extra bonus.

ref: https://homeguides.sfgate.com/clean-black-ceramic-sink-26479.html

I can vouch for the vinegar method. I even add a cup of it to my dishwasher every time I run a load of dishes to keep my hard water from leaving white marks on everything. In out toilets we clean with The Works toilet bowl cleaner as its the only thing that works there that will take off calcium build up in that situation. I would start with vinegar though, hose it down and let it sit as long as needed before scrubbing.

https://www.hunker.com/13421751/how-to-make-my-black-porcelain-sink-shiny

Vinegar or CLR should do the trick.

White cleaning vinegar should cut the residue. You can also use alcohol. We have one black sink - never again - it is a daily task to keep it from looking dingy.

This information may help:

https://www.bobvila.com/articles/how-to-remove-hard-water-stains/#:~:text=If%20it's%20tough%20going%2C%20try,less%20stubborn%20the%20stains%20become.

A paste that is prepared by adding baking soda to water has also proved useful to eliminate stains from black kitchen sinks. Take this paste on a clean cloth and then rub it on the site that has developed stains. The paste can certainly help to erase the stains from the sink. One can also use mineral oil to clean black kitchen sinks. Put small amount of mineral oil on the stained area. Now, rub it using a clean cloth to remove the stains.

I'd try vinegar or even a magic eraser!

Do not use Magic Eraser on a black granite sink. You will ruin it. Magic eraser is like a very fine sandpaper. What I do. is clean really well with Dawn dish detergent and very hot water. Rinse well and dry. Then use mineral oil. The stuff you get at the grocery store or Walmart in the drug section. It is approximately $2 for a bottle. It is food safe. Rub it into a dry sink and let stay overnight. You will probably have to do this monthly. If I had it to do over again I would not buy a black granite sink.

Hello vinegar is useful for hard water issues on shower heads and the area around vanity sink stoppers

Try a cleaner that has citric acid in it.

We usr CLR to remove all our hard water stains. It works well

Hi Linda, easiest safest way to do this is white vinegar, it dissolves those nasty hard water crusts. Use it full strength or diluted with water 1 to ratio rinse well when done

https://www.blanco.com/ca-en/support/cleaning-care/ceramic-sink-care/cleaning-ceramic-sinks-properly/#:~:text=Just%20get%20a%20soft%20sponge,t%20like%20these%20at%20all.

Vinegar or Alcohol have worked best for me.

I would try Cerama Bryte. Works great on my sink.