Paint expert Partrick Baty explains his work to the BBC Devon website
By Jemima Laing
Patrick Baty is a detective of sorts - but it is the provenance of paint rather than pilfering and pick-pocketing he investigates.
He works as a paint analyst and his latest task was to try to discover the original colour of Brunel's Royal Albert Bridge, which spans the Tamar.
The bridge is currently covered in 30 coats of paint.
Initial findings indicated that the original colour of the bridge could have been brown.
Patrick Baty is a paint analyst
All will be revealed on Monday 26 April, when Network Rail make public the results of Patrick's research.
After his findings are revealed, the two 455ft spans will be completely repainted.
A total area of 20,000 square metres - about three football pitches - of the bridge will be painted using the same three-coat painting system which is used on the Forth Bridge.
The Royal Albert Bridge was first repainted grey in 1911 and its original colour was hidden and never recorded, leaving a gap in the history books.
Speaking at the start of his project in October 2009, London-based Patrick told the BBC: "My brief from Network Rail is to try to work out how the bridge was first painted in 1859."
Patrick is taking blisters of paint back to London for analysis
"I believe - having carried out my reconnaissance - there's quite a lot of early paint on the bridge."
He works by taking samples of paint from various parts of the bridge for analysis which he has to do at night once the trains have stopped running.
"I use a hammer and chisel and give it a healthy thwack, and come away with a blister of paint," he explained.
"I'll set this in a clear polyester resin, cut through it and polish it and look at it under a microscope and we'll be able to see the layers of paint.
"Then I carry out a series of micro-chemical tests to establish when a particular layer might have been applied.
"Then I have to build up a story based on the documentary research I've carried out."
You can just spot two people on the top left of the bridge
The bridge was completed in 1859 - just a few months before Brunel's death - and it remains today as the only rail link to and from Cornwall.
The bridge had to be supported 80ft above water level, with a giant cylinder floated out and sunk onto the rock and the bridge's two 455-foot main spans were built on the shore, floated into position, then jacked up by a few feet per day until they reached the right level.
Ian Frostick, a civil engineer for Network Rail, said: "This is a significant year for the Royal Albert Bridge.
"The 150 years anniversary is a testament to Brunel's achievements and to the industry's commitment to this vital rail link."