Ceramics are not affected as much as organic materials by light and temperature but they, too, can deteriorate. High humidity can affect adhesives in old repairs, and mould can grow on animal glues if the temperature is too high and ventilation poor. Even too much heat from a tungsten light in a display case can dry out materials used for repairs.

Because of the high risk of breakage, ceramics are handled, moved and washed as little as possible. Large ceramics such as bowls can be cleaned with a soft lint-free duster (with no loose threads that might catch). Small ceramics with handles, knobs or raised decoration (such as figurines) are dusted with the tip of a hog's-hair brush with the metal ferrule protected with masking tape to prevent scratching. During the winter, ceramics are grouped together on a table for safety and covered individually with acid-free paper 'hats', so no further dusting is needed.

If ceramics need to be washed, a trestle table with a bowl of water is usually set up in the room where the piece is kept and a chemically neutral detergent used. (Household detergents contain additives and are unsuitable for precious antiques.) No piece is ever submerged in water. Instead it is meticulously cleaned with damp cotton wool swabs (avoiding any cracks) and tiny cotton buds are used to lift soapy water out of crevices. All ceramics are left to dry naturally.

The National Trust cares for more than 50,000 textile objects from state beds to samplers. All of them are susceptible to environmental damage - colours fade, fabric rots and the process cannot be reversed. However, further damage can be reduced by treating windows with ultraviolet-absorbent film or reducing light levels with shutters and sun blinds. Sometimes, with very important textiles, light has to be totally excluded as in the case of the State Bed hangings at Knowle in Kent. During the winter, textiles are stored in the dark using acid-free boxes and tissue.

As soon as the house is closed, tie-backs are removed and the curtains partially drawn to relax the folds. All precious textiles have to be handled with cotton gloves. Curtains and tapestries are cleaned only every year or two so, in between, they are vacuumed very gently to remove as much dust and dirt as possible. A small adjustable-suction-'museum vac' with attachments suitable for textiles is used on low or medium suction. Nylon mesh or muslin is fixed over the nozzle to prevent any loose threads from being accidentally sucked in.

This type of vacuum is also ideal for fragile carpets, once or twice a year with the nylon screening in place, or for gilt frames so that not even a spec of gold is lost. A domestic cylinder vacuum, however, can only be used safely on antique carpets and rugs in good condition. Once vacuumed, carpets and rugs are rolled up, pile-side out, around a wooden pole or PVC drainpipe (to allow dust to drop out of the pile), then wrapped in acid-free tissue and finally covered in down-proof dustsheets.

Valuable books

Most are in storage but those on display need special care during the closed season. Photos are handled with PVC gloves and given a light dusting with soft pony- or squirrel-hair brushes. Over the winter, they are stored in made-to-measure 'four fold flaps' - storage pockets that don't put pressure on the photos and prevent the emulsion layer from damage or silvering.

It's not just the 'front of house' that comes under the scrutiny of the housekeeping team. The kitchens of historic houses often still have their original fittings and contents that need to be protected. At Petworth House and Standen in West Sussex, for example, there's a vast collection of copper pots and pans in the kitchen that must be meticulously cleaned.

Gloves are essential to protect the copper from the acid in the cleaner's hands. Surprisingly, they use Autosol, a car metal cleaner, which has been found to be the most effective because it contains fewer chemicals than other brands and doesn't leave a residue which could attract moisture and cause corrosion. (Apparently it's also excellent for cleaning metal fire grates as well.) After cleaning, Renaissance Wax is applied to prevent tarnishing.

Many items in Trust properties are protected through the winter with their own made-to-measure cotton case covers. On upholstered chairs, a layer of acid-free paper separates the upholstery from the cover and protects the delicate fabric from being rubbed as the cover is put on and taken off. Small items - from desktops, for example - are packed away in boxes padded out with acid-free paper 'sausages' and 'doughnuts' made by the staff. Silver items are put into Tarnprufe bags (see box "The National Trust's top housekeeping tips"). Everything stays clean, dry and safe from damage until the new season.

For anyone who enjoys visiting historic houses, participating in a Putting the House to Bed day will not only give you some useful housekeeping tips, it will also give you a new perspective on 'the stately home'. Discovering how historic practice meets modern scientific knowledge made me see the contents of the houses in a quite different way.

Although the owners and housekeepers of centuries gone by didn't have the knowledge we have today, they knew how damaging light could be. Curtains were drawn and shutters closed when the country house was locked up for the winter and sometimes even when the family were in residence. Thanks to them, so many treasures have been saved for us to enjoy today. And as for the future, we know they are in safe hands.