noble just means: A metal or alloy, such as gold, that is highly resistant to oxidation and corrosion.

High-Noble Alloys
By definition, these alloys must have a noble metal content of at least 60 wt%, of which at least 40 wt% is gold. They usually contain a small amount of tin, indium, and/or iron which provides for oxide layer formation. This increases the alloy’s bond strength to porcelain by a factor of three. The disadvantages of these alloys include their lower rigidity and poor sag resistance during porcelain firing. There are three subclasses of high-noble alloys:
1. Gold-platinum
2. Gold-palladium
3. Gold-copper-silver-palladium
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