Conserving Virgin and Child with Cat, a drawing by Leonardo da Vinci

This drawing is on thin paper - the artist has traced the picture on the other side, reversing the image. It is drawn with a quill pen and iron-gall ink. Unfortunately, this type of ink is very acidic and, over time, can eat through the paper where the ink is thickly applied. The paper can become so brittle that the ink may fall out if the drawing is not repaired and carefully handled.

The repairs have to be done very subtly, as they are on the artist's original lines and can be seen from both sides. Japanese paper, which is thin, but strong, is used to support the ink and missing areas. The repair paper is coated with a heat-activated glue, which is stuck down with a small heated spatula. Small holes in the paper are filled with paper fibres or small pieces of paper cut to the exact size of the hole.

The surrounding mount must protect both sides of the drawing without hiding anything. A sandwich is made using two thin sheets of Perspex and the drawing is held at the corners with thin strips of silk. This is then inset into a traditional board mount.