I grew up in area that had lots of land fills over the years. But there were a few that were the first that I remember. The auto companies and supporting manufacturing companies in the Detroit area utilized these land fills for whatever crap was deemed unusable. Many times I witnessed railcars stopping alongside the landfills and attaching a hose to the tanker cars and opening the valves and away you go. No more waste to worry about. These landfills made it to the "Top 10" list for being the most toxic areas in the country. Getting to the point, I have found what I believe to be enamel paint dumped some 50-60 years ago by the auto industry. This material has been sitting and hardening all this time. It is brittle and fractures the same as what you have in your photo. It also has the bubbles within it. The color is very similar as well. It may be possible that what you are showing is some type of enamel that has hardened. It could be some kind of slag as well. I will post a picture of what I have found and you tell me if it doesn't look similar.
From Ward - July 22, 2012 at 00:18:00