Cut Polish Etch, Testing Welds, Roll the Tank

my online store is https://weldmongerstore.com/ that is how I pay for these videos. Can mixed welding gas become unmixed? or unevenly mixed? Science might say no but after a period of non use, rolling the tank sure seems to help the arc smooth out. I tested a mig weld about a month ago and saw a straight line indication. Was it a lamination? I wanted to do some further tests so that we could all learn something. I got an email from a retired metallurgist as well as a very good comment on youtube explaining the indication I saw. here is what the email said ... " Hi Jody, What you saw in today's video is not lamination. The weld would have been nowhere as good as it was - even noting the defects in it you described. A lamination would have blown apart. What you saw is rather light centerline segregation left over for the steel casting process. It is not a desirable condition but is acceptable for many applications, especially in lower carbon steel and where the steel is used flat or with easy bending involved. Centerline seg becomes a problem in higher carbon steel (the carbon and other alloying elements segregate toward the center line causing welding problems such as the formation of martensite in the heat affected zone.) I do not mean this to be a criticism but am writing you just for educational purposes. I really enjoy your videos and I have found them to be very educational even though I am one of those people for whom you explicitly did not start you videos for (university educated metallurgical types). I worked as a metallurgist for a large steel company for 34 years and have decades of experience with the type of steel you generally use in your videos. "