Appendix 6: Stabilising and drying methods (Guideline 5)

Freezing

For stabilising and restoring large quantities of records, or records that are already starting to grow mould, freezing is the most effective method. If there are only small quantities of records then other methods, such as airdrying, should be employed.

Freezing is a useful alternative for some records as:

• it stops the growth of mould and mildew (while the object is still frozen)
• it may stop bindings from warping, depending on the method of drying
• it stabilises water soluble materials such as inks and dyes, and
• it gives your organisation time to plan for recovery and restore buildings and equipment ready for the material.

However, conservators do not advise the freezing of vellum, photographs, glass plate negatives, electronic media such as diskettes, videos, cassettes or vinyl records.

As soon as the record quantities requiring freezing are decided, companies with appropriate freeze facilities (listed in the counter disaster plan) should be contacted and arrangements made for transport. You can:

• Blast freeze Commercial blast freezers are ideal as theydrop the temperature quickly and have a large capacity.
• Freeze in refrigerated chamber This could be slow but there are benefits to reducing temperature even before freezing point is reached.
• Use a home freezer unit to freeze small quantities quickly Ensure that it reaches a temperature of –10C and do not open until ready to remove the material (otherwise it will cause a freeze-thaw cycle).

Once the material is frozen and you have the time and resources to defrost and treat it, you need to look at drying options.

Freeze drying

The frozen items are placed in a vacuum chamber, which allows the water to evaporate without melting. This is of a huge advantage for water sensitive inks as it minimises the risk of them running further. Likewise it is also good for glossy papers as it prevents them from sticking together. But if these situations have begun freeze drying will not reverse it.

Vacuum freeze drying is not recommended for photographic materials unless there is no alternative, as their surfaces may be damaged. Leather and vellum may not survive. Volumes that are vacuum freeze dried should be acclimatised for at least one month before opening to avoid cracking the bindings, and monitored for mould.

It is important to have an agreement with a freeze-drying facility before a disaster so that costs, packing requirements and what items are suitable for the procedure are understood.

Dry air purging or dehumidifying

Dry air purging can be used if records are not soaking. A building or site is sealed in plastic sheeting and dry air, at least 26?C and 15% relative humidity, is pumped in using desiccant or refrigeration equipment. The water vapour is then absorbed in the dry air. This method is rapid and has the advantage of being in situ, but is only useful when the whole site can be sealed off.

Airdrying

Airdrying can be attempted if it is within two days of the disaster and if material is not soaked. Otherwise, mould will start to grow, and items that are suitable should be frozen. Airdrying may result in some distortion of items and should not be used for items with soluble inks.

Airdrying requires a large space with good air circulation and temperatures below 21°C. Circulation may be encouraged by positioning fans and opening windows. If available, dehumidifiers can be used in the drying process to reduce relative humidity (ideally to 25-35%). Screening material such as window screens can provide an excellent compact drying surface which allows for air circulation (although metal mesh will rust in contact with moisture).

Volumes

• Closed volumes can be cleaned before drying, by washing off dirt or mud on covers and edges using clean running water and a sponge.
• Books and volumes which can stand upright can be placed on paper towelling with their covers slightly open and their pages lightly fanned. A gentle breeze from a fan can assist the drying process. Do not use heat as it will encourage mould.
• Priority volumes can be dried by placing plastic sheeting on the floor, standing volumes upright with pages fanned (if their spines will support them), and then forming wind tunnels around them from cardboard or plastic sheeting. Cool air from fans can then be directed down the tunnels.
• Interleaving can be used for wet volumes that cannot support their own weight. Loose sheets of paper towel or blotting paper can be placed at 1 centimetre intervals though the volumes. Do not allow interleaving materials to exceed a third of the thickness of the volume or the spine will be damaged (the exception is with coated papers where each page must be interleaved). Replace interleaving materials when wet.
• If adhesives are sticking to the interleaving sheets, a release material such as nylon gauze should be used as a barrier between them.

Drying bound volumes by standing upright
reproduced with permission of National Archives of Australia

Pamphlets

• Pamphlets and loose pages can be hung on lines or improvised drying racks providing you have enough space and assistance.

Hanging small items
reproduced with permission of National Archives of Australia

Files

• Files should be removed from boxes carefully and laid flat. Bundles can be interleaved and pressed under a light weight or pages turned regularly, ensuring that the original order is maintained for each bundle. Cool air can be directed to the pages, but ensure that it is directed upward rather than directly on the pages. Replace the interleaved sheets when they become wet. Glossy papers should be fully separated and interleaved or frozen.
• For saturated files, metal binders should be replaced with plastic tubing or plastic coated wire and pages fanned with some interleaving.

Maps and plans

• Maps and plans can be interleaved with blotting paper stacked up to 10 high and pressed dry under glass, Perspex or thick board and weighted evenly.

Card indexes

• Card indexes should be removed from drawers, stack on sides loosely and supported at each end.

Vellum and parchment

• Vellum and parchment items are very fragile and susceptible to damage when wet. They should be fully supported at all times when being moved. Consult a Conservator before proceeding with any treatments. If nobody can be contacted interleave and freeze.

Photographic prints

If treated rapidly, photographic prints may be air dried. Photographs can be frozen if necessary but do not freeze dry as it may result in disfiguring marks on the surface of the photograph. To air dry:

• remove photographs from mounts or separate from each other to prevent the emulsion sticking
• rinse with cool water if necessary. Do not touch or blot surfaces, and
• place emulsion side up on blotters or lint free cloths or hang by placing clips on non-image areas, ensuring there is no overlap.

If wet, immerse in clean cold water in polyethylene bags. Send to a processing laboratory within 2-3 days for reprocessing and drying (except historic ones).

Photographic negatives

To air dry:

• remove negatives from envelopes
• wash in clean running water, and
• hang to dry or lay flat with emulsion side up.

Eastman colour film should only be handled by a processing lab. If there are large quantities of negatives they should be frozen and air dried.

If wet, negatives should be sealed in polyethylene bags and placed in plastic garbage cans under cold, clean running water while the negatives are still wet. They should be transferred to a laboratory within three days.

Glass plate negatives

Glass plate negatives should NOT be immersed in water. They should never be frozen or freeze dried. Air dry them immediately by laying flat onto blotter with the emulsion side up (duller side) or upright in a dish rack.

Fire

While water damaged materials do cause problems, simple techniques such as those described above can be used. The recovery of burnt collections presents additional problems. The effects of fire include heat, soot, burnt edges, melted coverings such as plastics, and possible water damage. The costs of restoration should be weighed against other alternatives. Burnt materials can be frozen, but any restoration other than basic cleaning, rebinding and rehousing should be left to an experienced conservator.