The process of putting a piece of sterling silver that has fire
scale in a kiln at 1300 degrees for 13 minutes to remove fire scale
sounds like a great way to develop a deeper coating of fire scale.
Fire scale forms on sterling silver when it is exposed to oxygen and
heated above around 1000 degrees.
The best way to prove the fallacy of this procedure is to put a
piece of sterling in the kiln and heat it to 1300 degrees.
The best way to get rid of fire scale is to not get it in the first
place. There are fluxes that prevent fire scale when soldering. Fire
scale can be prevented when vacuum casting sterling silver. Check
out Orchid archives for my very simple method of preventing fire
scale when vacuum casting.