The National Archives has one of the largest conservation departments in the UK. We spoke to John, who works in the manuscript area, about the process of conserving damaged documents.

What are you working on at the moment?

I'm working on a document from the series WO 12 - it is a high-demand document which is unfit to be handled by the public. There are 31 documents from this piece that have suffered extreme water damage, discolouration, mould growth, water staining and are torn.

How do you go about conserving it?
First, I arrange the fragments and brush over them with a very soft brush to remove surface dirt.

In this particular case, I decided to brush on a 2% solution of acrylic dissolved in acetone to consolidate and strengthen the paper. Naturally this is done in a fume cabinet.

Many of the documents are really badly damaged - some are in pieces, and others have lots of holes in them along with creases and cockles. Therefore, the next step is to arrange the pieces in order and try to ease out the creases.

Could you show us how you do that?

First I dampen my glass work-surface and put a polythene sheet on top of it, I then either dampen the surface with a sponge or flood the polythene with water…

With water? That seems incredible – to get these ancient documents wet!

Generally water has a strengthening effect on paper. It helps relax the fibres and allows us to ease out creases; it allows us to wash out dirt too. Obviously we test the ink first to make sure it doesn't bleed or spread. (Best not try this at home, folks!)

The fragments of the document are then arranged on top of the polythene and dabbed with a sponge to pick up surface dirt.

The next step is to join the fragments together.

Another layer of polythene is laid on top of the fragments to support them in order to turn them safely. I then apply a very fine "spider" tissue to the back of the document. The tissue is made of manila fibre which is very strong and almost transparent once applied. I do this using a light box so that I can make sure there are no wrinkles.

Before I start filling in missing areas, I have to make sure that the document is completely flat. This is done by pasting the document, using wheat starch adhesive, onto damp terylene (which itself has been pasted onto a Perspex sheet). The paper then dries under tension and, once it is dry, I can start infilling the missing areas.

Infilling is a very delicate operation begun by laying a sheet of polythene over the document. I then dampen the hand-made acid-free repair paper which is chosen for its close colour match and weight in relation to the original document.

The dampened repair paper is placed over the area to be infilled. I can see the outline clearly through the paper as it is lit from beneath by a lightbox and, using a mattress needle, I gently score the shape of the missing area.

The next stage is to score more strongly, dampen the surface once more and pull away the paper outside the scored outline - teasing out the paper fibres.

Then I remove the polythene from the document and position the repair paper directly over the missing area and stick it in place using wheat starch adhesive. A bone folder is used to blend the paper fibres along the edge. The document is then left to dry out slowly. When the document is completely dry, it is easily removed from the perspex by carefully pealing away the terylene which acts as a support for the document. The document is then placed face-down onto a clean blotter and the terylene can be carefully removed - leaving the backing of spider tissue on the surface of the document.

Where the edge of a document has been repaired, the paper is trimmed by hand to match the edge of the original document; with perhaps 1mm overlap to show that the original has not been cut into and to show that repairs have been carried out.