The picture-perfect green roofs of Parliament Hill's West Block have been replaced with shiny, new copper — and it could take 30 years before the look we've come to know in postcards is back.

What do copper roofs and mare's urine have in common? Local historian Don Nixon tells Robyn Bresnahan some intriguing stories about the roofs of Parliament Hill. 7:03

Don Nixon, a retired Public Works engineer who wrote a book about the Parliamentary buildings called The Other Side of The Hill, spoke to Ottawa Morning's Robyn Bresnahan about how the roof will evolve.

They used to mop the horse urine on the copper to make it go green faster. - Don Nixon

"It only stays bright and shiny for a couple of months and goes brown very, very quickly," he said. "It stays brown for about 30 years before it becomes green and then it stays green until the end of its life, which could be 80 years, maybe, or 100 years, maybe."

Aging copper turns green due to acid rain, he said, but legend has it our forefathers had a smelly way of speeding up the process when Centre Block was being rebuilt after the fire, between 1916 and 1919.

"Today we have cranes and trucks but back in 1916, they had hundreds and hundreds of horses — and a lot of horse urine," he said, crediting the story to former roofing contractor Doug Pickard.

"They used to mop the horse urine on the copper to make it go green faster."

Specifically, the potent urine of pregnant mares sped up the greening process, he said.

The new copper on the roofs of the West Block likely won't turn green for 30 years. 2:06

Roof will soon look like 'chocolate bar'

Wonder why there's no attempt to try to keep the copper shiny?

"That's artificial. That wouldn't be right," Nixon said. "It's like a person. I mean, I would like to look young again, I guess, but it's life and a copper roof goes through this life cycle."

For now, he said we'll just have to get used to a different-looking West Block, which is also surrounded by cranes and scaffolding as it undergoes a major facelift.

"It's somewhere between new copper, which is bright and shiny like a copper penny, and what's it's going to look like in two months from now, which is a Cadbury chocolate bar," he said.