I trust S&S Stalkers observations, that virgin 2" black ice looked pure a solid.
There is much to understanding ICE and what can be determined as "safe" or not. Its never just all about the thickness, age of ice or type. Air temperature is another key factor.
Below is a link to perhaps the most comprehensive resource available for anyone who wants to venture out, or just understand more about ice.
Included are important designs of safety equipment required.
The author Bob Dill from Vermont has compiled this website, he is avid Nordic skater & Iceboater with a lifetime of experience.
I am happy to have contributed a few pictures, and I sail on Windsurf type Iceboard and have 35 consecutive years of exploring vast regions of ice in New England.
I make time to stop and chat with most ice fishermen, being avid fisherman myself, what to know whats getting caught, but mostly I am interested in your "core sample".
Sharing ice thickness information is critical to safe participation for whatever you do out there on it!
Hope to see you out there!