What is the origin of the saying "made of sterling stuff" and what is "sterling" in this context referring to?

I thought it was 'made of sterner stuff'? I've never heard of sterling stuff..

Sterling refers to a type of silver that is rust resistant. Most commonly used in cooking dishes and utensils. Saying something is "sterling" means that it is of good quality and won't lose its luster over time.

Means 'thoroughly excellent'. So saying someone was made of sterling stuff would mean they are a thoroughly excellent guy -edit- @thewritz Sterling silver is not rust resistant. Firstly, silver does not rust, it tarnishes. And secondly sterling silver tarnishes at a faster rate than pure silver. Sterling silver is silver with a small amount of copper added to make it stronger, as pure silver is too soft to be useful. It is nothing to do with how it looks or its quality.

Means 'thoroughly excellent'. So saying someone was made of sterling stuff would mean they are a thoroughly excellent guy -edit- @thewritz Sterling silver is not rust resistant. Firstly, silver does not rust, it tarnishes. And secondly sterling silver tarnishes at a faster rate than pure silver. Sterling silver is silver with a small amount of copper added to make it stronger, as pure silver is too soft to be useful. It is nothing to do with how it looks or its quality.

Sterling refers to a type of silver that is rust resistant. Most commonly used in cooking dishes and utensils. Saying something is "sterling" means that it is of good quality and won't lose its luster over time.

If you are a lot more interested in understanding to communicate Spanish than read or publish it (they do teach reading through and creating but speaking is far far more heavily emphasized)