How can you tell the difference between “young ice” and “old ice” (sailing)?

Question

I’m reading a book on Ernest Shackleton and it’s really interesting. He keeps mentioning the age of ice though and I’m wonder how he can figure this out.

In: Chemistry

Answer 1

I’m guessing here but I’d suppose young ice has a deeper color, like deep blue, and as it ages and more cracks appear that fades out?