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There have been quite a few questions about this post. Here are some of the common questions and the answers.
What is Dawn?
Dawn is a brand of liquid soap used to wash dishes.
Will a different brand of soap work?
I used Dawn and didn't test any other brands. If you try another brand and it works, leave a comment and let me know!
I forgot to warm up the vinegar. Will it still work?
Yes. After cleaning the glass the first time, I had plenty of cleaning solution left over. I used the left over solution a few months later and didn't warm it in the microwave. It still worked!
Antique glass door knobs can range anywhere from $10.00 up to $50+. Try checking on ebay.com. They have a bunch on there.