didnt read the article but I am assuming it is the material they are working on. copper and iron are easy to handle but aluminum is a bit harder and then there is stuff like titanium which recuire very high skills… and all those cases with titanium with steel or whatever. they need to know what they are doing. …. got my information from my ex roommate who welded bikes with titanium and he was a highly skilled enthusiast.

https://www.cwbgroup.org/association/how-it-works/how-it-wor...