Restoration and Conservation of Delicate Materials With Mold


The problem is: how to conserve and restore delicate materials such as leather or vellum books, paper books, documents, archival records, art works and textiles after water damage once they have mold without damaging the object. Most of the commonly used mold treatments such as regular heat sterilization, methyl bromide, ethylene oxide and ozone bleaching can damage or destroy the delicate structure of a leather or vellum books, paper books, documents, archival records, art works or textile being treated while they are killing the mold or bacteria. This risk to the materials, not to mention damage to the environment, are now of critical importance. The solution is a two step process: vacuum freeze drying and plasma fumigation.

Most water-damaged materials will show signs of mold growth after a short time. Initially, water damaged documents and books have to be blast frozen to minimize large ice blocks which can further damage leather or vellum books, paper books, documents, archival records, art works and textiles. Next, normal freeze drying is used to remove the moisture from water damaged materials. Unfortunately, normal freeze drying has its drawbacks. Freeze drying removes the water, but not the mold and/or bacteria. This is because mold has a protective mechanism within its life cycle which can help it to survive against such extremes as freezing and desiccation by forming rough, thick-walled, protective coatings called zygosporangia. These coatings allow it to become metabolically inactive until such time that conditions improve, for example, conditions where the temperature is warmer and there is more moisture present. Many laboratory suppliers make use of this mechanism and commercially freeze-dry mold samples to sell to researchers. Therefore, normal freeze drying is not enough in the presence of mold or bacteria. Only through further treatment can mold and bacteria be inactivated.

Vacuum freeze drying and plasma fumigation are non-toxic, chemical free treatments that have been developed and tested which use no ozone bleaching or nvironmentally dangerous chemicals to treat delicate materials with mold after water damage. There are no harmful gasses or waste to be disposed of after the treatment. Through the vacuum freeze-drying process, a process normally used in decaffeinating coffee, and a secondary process called plasma fumigation, we are capable of reducing molds by 95%. Independent clinical tests prove that this two-stage treatment method using supercritical/near supercritical carbon dioxide, effectively destroys molds and bacteria after water damage and is suitable for all types of delicate materials such as leather or vellum books, paper books, documents, archival records, art works and textiles. It took seven years to develop this environmentally safe and non-destructive combination of methods for mold and bacteria inactivation.

Once vacuum freeze drying has been performed, the real innovation is in continuing the process of decontamination using a plasma fumigation. The plasma is generated using a dielectric field and a special mix of gases which are all contained in a customized vacuum chamber. Plasma is considered by physicists to be a fourth state of matter. It is a highly ionized neutral gas in which the number of free electrons is approximately equal to the number of positive ions. Particles present in the plasma, such as ions and free radicals, have a high activity and do the work on moldy materials including books, documents, papers, photographs, manuscripts, maps, slides, microfilm, microfiche, x-rays and books. Their high activity is related to the process pressure. After plasma treatment, the materials are treated with carbonic acid. Carbonic acid (H2CO3) is a dibasic acid which is formed when carbon dioxide is dissolved in water. It is a chemical reaction which occurs in nature when rain water is formed.

CO2 (gas) + H2O(aq)? H2CO­3 (gas)

Under specially controlled conditions, this carbonic acid is introduced along with applied heat to effectively sterilize the affected material being treated including the mold. This may occur due to the unique mass transfer properties of super critical/near supercritical CO2 which may allow the fluid to penetrate the cell walls and interact with the intracellular components of the mold. This sterilization is a function of both the proximity to the fluid’s critical point and the chemical nature of the fluid itself.

Materials And Methods

To test our treatment we used conventional microbiological procedures and did multiple tests on areas of water-damaged, mold infested documents. We took samples before and after treatment and then analyzed the samples. The samples were also independently analyzed.

Media – Potato Dextrose Agar.

Materials – Petri dishes.

Methods – Serial dilutions.

Conditions – Aseptic conditions. Samples were incubated at 37°C in a constant temperature growth chamber.

Results And Discussion

We identified the most prevalent mold present took a colony count. The most abundant molds were identified as the common paper molds: Fusarium, Oxysporum and Penicillium notatum. The colony counts were measured in Colony forming units (Cfu’s). In-house test results were able to show that the mold had been reduced by 2-3 log orders. Of 5 samples taken – mean initial cfu’s 28,000, mean final cfu’s 1,307, a reduction of 95.33%. This was consistent with independent laboratory results, but with the added advantage that the results were available after 48 hours.

While growing cultures may permit greater accuracy in speciating some fungal organisms present, the ability of spores to grow and compete on laboratory media can differ significantly with their ability to grow and compete on a more real world substrate such as a file, document, book or textile.

However, for our needs the use of this type of analysis is very useful. Firstly, it gives us a feel for the degree of mold infestation and thus the level of treatment required. Secondly, as the mold is being grown on an agar plate, the humidity conditions are very high, almost 100% RH, particularly while the agar is wet. As humidity is perhaps the single most important factor which affects mold growth, cultivation on agar should give living mold the favorable conditions that it needs to reactivate, release its haploid spores and re-colonize its new substrate. In short, using this method lets us know that we have done our job.


Consider the reality; molds have a high natural incidence. Penicillium and Fusarium for examples have 6% and 5% presence respectively in an average sample of outdoor air. This fact combined with molds’ complex survival mechanisms, make 100% mold eradication an unachievable goal. Our results were a 95.33% mean reduction, which we consider a good outcome as the mold was significantly eliminated and important documents were saved and rendered safe for normal handling.

A few or trace amounts of fungal spores in surface sampling should be considered background and be expected. In this investigation our methods were tested on fungal species that were found on documents, the most significant but not exclusively being common paper molds: Fusarium, oxysporum and Penicillium notatum. We are conscious that these are not the only fungi that which infest books, legal documents, works of art and personal collections but we feel that these methods could be applied equally to any rapidly growing, asexually reproducing fungus.

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