Conservator Lorraine Finch with the memo she is working on
A short note written and signed by Admiral Horatio Nelson more than 200 years ago is being restored ahead of a display due to open next year.
The requisition for suet and fruit to supply his ship The Minotaur was donated to the Norfolk Nelson Museum in Great Yarmouth, Norfolk.
For two centuries it was glued to a piece of paper stuck to a backing card.
The conservation work, costing more than £300, is funded by the museum selling second-hand books.
Horatio Nelson, who led the British Navy, saved Britain from the threat of invasion by Napoleon in the 1800s, but died in battle at Trafalgar in 1805.
Lorraine Finch, a freelance conservator who is carrying out the work, said the note would be cut from the card, and soaked in water to release dirt and dissolve the glue.
"My first job was working for four years on the letters of the first Duke of Wellington, who lived in exactly the same period, and I've never had one run yet.
"This type of ink is iron galling and it's very stable in water.
"I can see that this won't run but if I had an object I was concerned about, I would use a hair dryer to take out the water as soon as anything is seen moving - but this won't run."
The memo states: "Supply the Minotaur one [blank] suet and fruit."
It was addressed to the commanding officer of the ship Ajax and is signed Nelson + Bronte.
Faith Carpenter, curator of the Norfolk Nelson Museum, said: "We were very lucky when we were offered a pile of items.
"I was amazed to find a Nelson letter in there.
"We've never been donated a Nelson letter or memo before.
"Valuing it is really hard because it could be worth everything or it could be worth nothing.
"It depends who's prepared to buy it but we're not selling."