The brown spots which frequently appear on old paper, commonly referred to as foxing, can be very disfiguring to an image. There are various causes including mould and tiny bits of metal in the paper, particularly iron which has oxidised and turned to rust. Any specks of metal need to be removed or the stain can spread. A mild bleach is used to reduce the brown spots. If they are very dark it is sometimes better to leave them paler and less obvious than to try to remove them altogether. Continued bleaching weakens the paper structure and could lead to creating small holes in the paper where the spots were.

Paper is easily damaged by rough handling, being rolled and folded or put into a drawer where it gets pushed around. Tears are repaired using Japanese paper and conservation quality starch paste as an adhesive. If the damage is extensive, as was the case with the map of the farm, the image can be pieced together first using strips of Japanese paper and then the whole thing is lined using the same materials. Any holes and missing areas are filled using paper that is as close to the original as possible. These are toned to match the original or painted in to hide them.

Paper that has become creased or wavy, often described as cockled, can be flattened using a variety of methods once the paper has been relaxed by getting it slightly damp. In cases where the creases are particularly bad or the paper has cracked along them it can be best to line the artefact with Japanese paper and starch paste and then stretch it out while it dries, which is how the cartoon (below) was treated once the sellotape had been removed and the tears repaired.

As paper ages it starts to get browner as its fibres decompose. The speed of degradation depends on the quality of the paper in the first place but this process is speeded up by sunlight, acidic conditions created by poor quality mount board or wood and by changes in temperature and humidity. The sailing ship at anchor had a mount which protected the edges, probably from direct sunlight. The other picture of boats (below) has vertical lines showing the edges of the 3 bits of wooden backing behind it.

Once the paper has started to go yellow the colours appear changed. Reducing the discolouration can help to restore the original colours and balance of a picture as can be seen from the portrait of the man.

Often stains are caused by pictures getting damp and the soluble brown colouring from old paper moves with the water leaving tide lines across the paper. When this has happened washing the area with water will generally reduce the stain. Sometimes more permanent colours from the paper are moved as well which are harder to remove and require the use of alternative treatments.

Unfortunately when pictures get damp they often go unnoticed for some time leading to mould growing. The stains caused by mould are much harder to treat and can rarely be removed altogether. The mould also attacks the fabric of the paper leaving it considerably weakened in those areas. If a pictures gets wet it is always best to remove it from its frame as quickly as possible to let it dry. In warm conditions damp paper will grow mould very quickly and certain types of paper and pictures, particularly photographs, will stick to the glass if left.

Stains from sellotape and masking tape can usually be reduced with solvents but it can depend on the age of the tape and the medium used in the image.