The sail has 90 shot holes from the Battle of Trafalgar
The only surviving sail from the Battle of Trafalgar is being preserved for history by a team of textile experts.
HMS Victory's fore topsail now lies in an "environmentally-controlled tent" while the process to clean it continues.
It is not an easy job with the sail boasting 90 shot holes from the battle on 21 October, 1805, in which Admiral Lord Nelson was fatally wounded.
Experts from the University of Southampton's Textile Conservation Centre and Mary Rose Archaeological Services Limited are undertaking research to find the best way of removing potentially harmful acidic soils from its surface.
A team of six textile conservators is involved in the current cleaning programme.
HMS Victory can be seen at Portsmouth Historic Dockyard
They are using a low suction vacuum cleaning process to remove fibres from the heavily-soiled sail.
Those fibres are then analysed to determine the strength of the sail and its long-term needs.
Lieutenant Commander Frank Nowosielski MBE, Commanding Officer of HMS Victory, said: "The Battle of Trafalgar is a seminal event in our history and the fore topsail is an unique artefact.
"We must ensure we safeguard it for future generations and the steps we are now taking should allow this."
The sail itself remained on board HMS Victory until the ship returned to Chatham for repairs in January 1806.
For the next century, the history of the sail is obscure.
Large painted letters stating "Victory's Topsail" suggest it was displayed at some time before being returned to the ship for the Centenary of Trafalgar.
Years later, it was rediscovered in the gymnasium in the Royal Naval Barracks HMS Victory, known as HMS Nelson today.
It was then returned to the ship in 1967.
The sail was seen by the public at Portsmouth's International Festival of the Sea in 1998 where it was displayed in an experimental vertical fashion.