Painters have been working on the bridge for more than a century

The need for continuous maintenance of the structure has passed into folklore and led to the coining of a phrase for a never-ending job.

However, Network Rail has announced a £74m contract which will see painters down their brushes in 2012.

The new paint has an estimated life span of 25 years, although is it hoped it will last closer to 40 years.

The expression "like painting the Forth Bridge" features in the Cambridge International Dictionary of Idioms.

It states: "If repairing or improving something is like painting the Forth Bridge, it takes such a long time that by the time you have finished doing it, you have to start again."

The restoration of this remarkable bridge will return it to near pristine condition

Marshall Scott

Balfour Beatty

For more than 100 years, that is how painting work on the bridge has been carried out.

However, Network Rail's chief executive, Iain Coucher, said the company was now able to name the date when the process would end.

He said: "The work currently being undertaken will restore the bridge to its original condition and preserve the steel-work for decades to come.

"The team currently working on the bridge has now completed some of the most difficult work and they have already overcome the most significant challenges that this project posed."

The work involves screening off sections of the bridge before old paintwork is removed and any repairs carried out on the bare steel.

The new paint, similar to that used in the offshore oil industry, is then applied in three coats.

Marshall Scott of engineers Balfour Beatty said: "We have now worked in excess of 2.4 million hours on the bridge over six years.

"We now look forward to taking this project to completion in 2012 and, with the removal of the scaffolding, the restoration of this remarkable bridge will return it to near pristine condition."