[jchcollins]

Originally Posted by jingram058

Normal cardboard stock for the card, not too thick, not too thin, but dense, no light coming through when held up to a lamp

Again, this is where experience is almost essential. Different vintage cards can have vastly different cardboard stock. A 1956 Topps card, for example - is going to feel nothing like a 1970 Topps card in terms of thickness. The 70's are much thinner. I think the general rule is that Topps used crappier cardboard stock as 50's became the 60's, and then the problem got even worse as the 60's became the 70's. But there are differences within decades as well. 1958 Topps cards are generally slightly thicker than 1955 Topps cards. It takes handling of the cards over time to get familiar with things like that.