Keeping the clocks clean is important for their longevity and legibility. Dust, dirt, or smudges on clock faces can make it difficult to read the time accurately. Regularly wiping down the clock surfaces with a soft, lint-free cloth and, if necessary, using a mild cleaning solution can help maintain their appearance and readability.
2) Then safely clean the glass or front face of the clock. See below image for your better understanding.
Note: Do not press the glass directly as it can break the glass and may hurt you. Don't tighten the glass so much that it doesn't open next time when you need to clean it. Also, make sure the glass and brass border is 100% Dry while closing it.