Preventive conservation slows down the deterioration of an object by protecting it from physical and biological damage and by moderating the harmful elements of its environment.

It involves controlling visible and ultraviolet light levels, maintaining favourable relative humidity and eradicating insects and other pests.

All materials deteriorate eventually, some more quickly than others. To such naturally destructive forces as fire, water, light, pests and damp, man has added over-heating and atmospheric pollution.

Two approaches are adopted to combat these forces:

• remedial conservation which endeavours to put right the effects of previous deterioration

• preventive conservation which is designed to keep future deterioration to a minimum

Remedial conservation

Remedial conservation can never be more than partially successful and is often extremely expensive.

Clever repairs may partly conceal, but still cannot alter, the fact that damage has occurred. A restored object can never again be an object in original condition. Nor can some further loss during the process of repair be completely avoided.

Preventive conservation

By contrast, preventive conservation is not only cheaper in the long term but ethically preferable. It preserves the historic and artistic integrity of an artefact, rather than compromising it by restoration.

Housekeeping is concerned not only with the care, cleaning, handling, condition-checking, packing and storage of a wide range of different objects and materials. It is also about the control of light, relative humidity and temperature levels.

Originally with only a limited number of visitors, country houses were cared for by an army of servants.

Now, with visitors by the thousand, the Trust cares for these same houses with a small complement of dedicated staff.

It is able to do this by combining the tools and methodology of modern conservation with traditional good housekeeping practices.