The special effects director for Merlin, Colin Gorry, has written a blog post in which he reflects on his work on the show.

On the BBC website, Gorry has posted a lengthy account of the work he did on Merlin, writing that, “Working on Merlin was a delight and a privilege. It was a rollercoaster script full of magic and natural effects (like rain, mist, wind, fire, a net trap etc) – a lot of which could be shot front of camera.”

He describes working with up to six technicians to create the various effects, and names some of the biggest challenges, like controlling the direction and speed of a boat around a moat.

Whenever they had to have actors fall over, “we incorporated a hidden system of wires and pulleys into the set, and the mattress had to change direction too, so some lines needed to be released or extended during its travel. It was basically a puppet moving on the horizontal plane.”

As for the iconic effect of the dragon breathing fire, “we specially constructed pressure vessels to hold propane gas.”

But whatever Gorry and his team was working on, it was “always an immense amount of fun to work out, work on and produce.”

The series finale of Merlin will air on December 24.