Blackman joins on a season-long loan deal from Chelsea.
“I'm buzzing, it's been a very long process, obviously when you go for the Premier League lads you have to wait for them to come back and everything else," Warne told themillers.co.uk.
“Jamal has always been high up on our list so it's good news, we're really pleased with how Chelsea helped us get the deal over the line and I'm looking forward to watching him.
“I've done loads of research on him, he's used to the area and he knows this is a hotpot of football, so generally he gets the area. He's looking forward to starting like they all are, we're getting to the point now where it's less than two weeks until the first competitive game and we'll see where it takes us."
Warne insists that Blackman fits the ball of the calibre of goalkeepers he wants to bring in to the football club.
“I like my 'keeper to be big and brave and he's definitely that. It shows what sort of goalie I want, the goalkeepers I really like have already been snapped up by Premier League clubs. Marek (Rodak) was unbelievable for us for two years and the same with Dan Iversen, if I could have kept him for two years I would have, but it wasn't the case.
“We encourage our 'keepers to come for things, to come and be brave. If he comes for something and drops it that's not his fault it's mine because I push them to come for stuff so hopefully he'll be good competition."