The legend goes that once you finish painting the bridge work has to start all over again because of the scale of the task.

But Balfour will finish its ten year, £130m contract within weeks and the bridge won’t need another full paint job for another 20 years at least.

David Simpson, route managing director, Network Rail Scotland said: “Over the last decade, the bridge has been restored to its original condition and its new paint will preserve the steelwork for decades to come.

“The paint system being used on the bridge has been used in the past on north sea oil rigs. We expect it to last in excess of twenty years but we will be back from time to time to maintain the most exposed sections of the structure.”

The current project involves more than the straightforward application of another layer of paint.

Scaffolding access is erected and screened off from the environment before old layers of paint applied over the last 120 years are removed using an abrasive blasting technique.

Steelwork requiring maintenance is then repaired before the new paint is applied in three protective layers.

Marshall Scott, managing director, Balfour Beatty Regional Civil Engineering, said: “By working together in a close relationship, Balfour Beatty Regional Civil Engineering, Network Rail, the principal subcontractors and the workforce involved in undertaking this complex programme of restoration have successfully delivered a project requiring safe systems of work to overcome some of the most difficult of working conditions.

“The now fully restored Forth Bridge will continue to operate for many decades to come and it will provide the world renowned image that Scotland can be rightfully proud.

“The work that Balfour Beatty Regional Civil Engineering has provided to restore the Forth Bridge back to its original condition will remain as part of a legacy and a testament to the skills and expertise of those who built this much treasured structure more than a century ago”.

The main subcontractors on the job are Pyeroy, Harsco Infrastructure, RBG and ThyssenKrupp Palmers.