What is freeze-drying documents: when is it used?

Massive floods, burst pipes, firefighting, flooding, even constant exposure to damp conditions endanger archives, records and libraries. While many of these situations cannot be foreseen, we can take appropriate measures to minimise the damage.

A rapid and effective response is key to reducing physical damage and biological contamination of the books or documents concerned, especially given the impossibility of dealing manually and specifically with thousands of documents at a time.

Let’s see how freeze-drying becomes the most effective process for the recovery of high-value books and documents that have been completely soaked after a flood.

In such catastrophic events where hundreds, thousands of documents have been damaged by water, freeze-drying documents has become the most reliable and effective technique for restoring damaged items.

The process consists of freezing as quickly as possible all the affected documents or books, in order to reduce their physical alteration and biological contamination, as well as to stop the loss of pigments or original inks. It is also important to act before the cellulose of the book or file becomes a block.

Once the freezing process is complete, a special high-pressure vacuum chamber will be used, in which, when the time comes, with the right levels of temperature and pressure, the moisture will be sublimated (the water will pass directly from solid to gaseous state). At the end of the process, the freeze-drying technique will have removed the moisture from the documents, stopping the proliferation of mould and avoiding complications such as adhesions, stains and deformations.

However, the quality of the restoration will depend on the material being freeze-dried. There are some pieces made of different materials with different absorption properties that could be deformed due to the different rates of drying and expansion.

These are some of the typologies that can be freeze-dried with good results:

• Books and manuscripts:

  

  Textbooks, antiquarian books, coated magazine and pamphlet papers, leather, parchment, vellum, drawing linen, pulp paper, etc.

• Paper records and documents:

  

• Works of art:

  

  Drawings, watercolours, tapestries, embroidery, acrylic paintings, etc.

• Historical documents:

  

  Maps, stamp collections, currency, newspaper articles, etc.

• Souvenirs:

  

  Leather and fur items, recipe books, scrapbooks, photographs, letters, cards, etc.

As we have seen, freeze-drying is a fast and efficient process that is particularly suitable in the following cases:

• When a large number of water-affected documents or books need to be recovered.
• When the documents are not only damp but also soiled with mud or soot.
• When there is a clear risk of deformation or distortion.
• When damaged documents are irreplaceable or more costly to replace than to recover.

In any case, once undertaken, the process of drying documents is not without its difficulties. It is important to realise that the success of this large-scale salvage system will depend above all on our ability to stop the development of mould.

In order to do so, a number of measures will be of vital importance:

1. Carefully separate mould-contaminated objects from non-contaminated ones, including when packaging and freezing them.
2. Do not return specimens to the shelves until possible mould contamination has been fully treated. Widespread infestation could cause irreversible damage.
3. It is recommended that, after the drying cycle, all mould-contaminated materials be sterilised.
4. Recovered material should be kept in a controlled environment with a temperature of 10-15°C and a relative humidity of 35-40% to keep the mould spores inactive.
5. Returned material should not be accepted without assurance that it will be returned completely dry.
6. After the freeze-drying process, documents should remain unpackaged and on open shelves in well-ventilated rooms, monitored daily for at least one year.
7. If the material remains in boxes, it will be impossible to detect the presence of mould in its early stages.

The freeze-drying process itself is divided into three phases: the freezing phase, the evaporation phase (by sublimation) and the hydro condensation  phase.

1. In the first phase, the documents are frozen to maintain their shape and structure. The water that impregnates them is frozen in the processing chamber.
2. Next, a high-pressure vacuum is applied in the freeze-drying chamber and, by heating, the frozen water is evaporated directly.
3. Finally, a gradual increase in temperature completes the process by expelling the vapours, which are condensed externally and discarded.

However, if the best results are to be achieved with the freeze-dried archives, organisational tasks will also require time, but will contribute to the success of the enterprise. We are talking about organisation and rehabilitation a priori, and monitoring and preservation a posteriori. Here are a few tips:

• Create a map of important documents, those that must remain original and those that can be copied. Also choose those to be located in the most secure areas with low humidity. With some items, replacement may be more convenient than restoration.
• After freeze-drying, provide a drying area with twice the amount of space that the documents occupied, so that this space allows the material to regain its environmental balance and allows you to compensate for the effects of those books that have expanded. This can take a couple of weeks.
• Finally, for at least a year, carefully inspect the pieces once they have been thoroughly cleaned and restored, to detect any early presence of mould.

CURIOSITIES BARNALAB freeze-dried products:

The main advantages of freeze-drying wet documents include its environmental friendliness as it does not use chemicals, its efficiency and cost-effectiveness in the medium term, and the speed with which it can act on large quantities of material.

Source of the cover slide: americanlibrariesmagazine.org