Oh man! I just went through a lo-o-ong discussion where I asked the same thing! I bought a Model 66 (a close cousin of your Model 19) in excellent, spotless condition. Took it to the range once and then noticed the rings after the cleaning. It drove me crazy because I thought it was a carbon built that I can not clean off.
After all I was told that this is how cylinder chamber is made. Look up a long cleaning related topic under my name, you'll see... and leave these rings alone, they are there by design
