### Step-by-Step Solution for Coating Mirrors
1. **Preparation of the Coating Compound**:
- Begin with a compound that contains silver (Ag) and ammonia (NH3). This compound is typically silver nitrate (AgNO3) dissolved in ammonia.
2. **Reduction of the Compound**:
- Add formaldehyde to the compound. The formaldehyde acts as a reducing agent, converting the silver compound into metallic silver (Ag). This step is crucial as it transforms the silver ions into a solid form.
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