This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A good way to clean gold or platinum jewelry is to first brush with soapsuds, then dust magnesia powder over the article and allow it to dry. A few rubs with a cloth makes the article shine with great luster. As magnesia powder is highly inflammable, it must be kept away from fire.