In the jewelry world, gold plate and silver plate are usually base metal products (brass, nickel, etc) that have been coated with a thin layer of said metal, most often through the process of electrolysis, also known as electroplating. The difference between the gold karat descriptions is the purity of the gold used to coat whatever item, also resulting in the difference of the color of the finished product. If a gold plated item does not carry a karat number, that means the purity of the gold used in the process is questionable (as determined by the FTC guide
If a jewelry item is described as 'gold tone' it means that the item is gold in color only, which may have been done with a very thin gold 'wash' but does not contain enough gold to be measurable, and is also know as 'gold flash'.
Yes, silver 'plate' does contain real silver.
Answer contributed by Dale "Cougar" Armstrong