How to breed an Opal Dragon in Dragonvale

To breed a Quicksilver Dragon all you need is to try and breed a Metal Dragon with a Water Dragon. Note that you might also get a Rust Dragon. It's breeding/egg time is 18 hours. If your breeding time is 6 hours, you got a Rust Dragon instead.

Note Water/Metal hybrids also work when breeding, but hybrids have a munch lower chance of getting you a Quicksilver since they can result in other combinations.

From the Dragon Vale Wiki

The Pollen Dragon can be bred by selecting an air dragon to mate with a plant dragon at the Breeding Cave/Epic Breeding Island.

And the breeding time is 7 hours whereas the Willow Dragon is 8 hours.