Instructions
Rinse the bottle in tepid water, around room temperature. Extremely hot or cold water can cause cracks in older glass.
Allow the bottles to drip dry upside down overnight to remove any excess moisture.
Use a sponge to apply a small amount of cleaning product to the bottle if it is beginning to get hazy or dirty. Rather than a commercial product, use either a 50/50 mix of water and white vinegar or a can of cola. Rinse with water afterwards.
Contact a professional bottle cleaner, especially if the bottle is valuable. You can find a professional cleaner in your area by inquiring at an antiques store or auction house. They can restore the bottle properly without overcleaning and thereby devaluing it.