its desribed as being an organic steel... when he changes to his metal form he becomes extremely durable (his skin is rumoured to be tougher than the hulk's, he just doesnt have a healing factor), the cool thing is that the metal skin doesnt make him slower or less agile, he keeps all his mobility...
I, too, would love to see a real fight between Wolverine and Colossus. Colossus would mop the floor with him. Wolverine just does not have the strength to pierce Piotr's metallic skin.
Oh, and that scene from Ultimate X-men #1 (I have it, by the way), I wouldn't really count that as Wolverine cutting through Colossus, since it was indeed a virtual reality training simulation. The simulation did not have the same stats, abilities, and skill that the real-life counterparts do. For example: Jean would would've easily blocked that optic blast from Scott (Which Wolverine made happen by twisting Scott's neck to face Jean and pressing the visor button) and Iceman would've froze him instantly. Beast would've knocked Wolverine out with that first kick of his, or Storm would've struck him with lightning. That training simulation was just not a very good source to go by.
Not sure really. I don't know if they would have the same piercing power as blades. Yes, they would have more force, but I'm not sure that they are efficiently designed to pierce.
Perhaps armor-piercing adamantium bullets. That might do it.
He can't unless he was propelled with enough force. He could scratch it at the most. Having extremely sharp claws doesn't mean you can go through any thing. People fail to involve strength.
Once he his skin also got cracked once. He was heated up then frozen, like freeze thaw. And his skin cracked, I don't think that would happen with Admantium (the main type)
in ishue 152 of the origanel uncanny x-men comic the brood showed up at a construction site and was going to shoot and kill prof-x missed and hit colloses the shot started to melt through colloses and he was allmost killed by it so he was not involnarable in a real heated fight i think old wolvie would chop him into cold cuts and serve him up. (i think it was 152 it was some where close to that )