Cover your cough and stay home 
… take advantage of the learning lists …
Also please Read how to post code blocks in the forum …
Lastly there is a specific Ruby subcategory for SketchUp Ruby coding …
… (I’ve reassigned your topic.)
P.S. - Changed “Ruby” in topic title to “API calls” as it isn’t Ruby that creates duplicate material objects, it is the SketchUp core that does this to ensure unique material names, because of the way you were coding.