EditorMeet the microbe: why water and books don’t mix
Karen Bartlett is a professor in UBC’s School of Public and Population Health, and her Preservation Week talk gave us a glimpse into the role of fungi in the deterioration of our books and archives, as well as the health risks to people who have to work with and around mouldy books.
Mould (and fungi in general) is usually mentioned in a negative light, but Bartlett remarked that “life would not be worth living without microbial products,” including beer, wine, leavened bread, miso, and soy sauce, among others.
Fungi are nature’s composters, said Bartlett, and to them, a leaf off a tree and a leaf in the book look identical: they are both organic materials that can serve as food sources. Moulds consist of filaments called hyphae, which can be specialized into spore-producing structures known as conidiophores, as well as root-like structures that penetrate the substrate of organic material and secrete enzymes into it, breaking it down. So when moulds colonize a book, they are actively destroying its pages.
Most moulds prefer a temperature range of 4°C to 30°C, which is good in a way, because it means that very few of them thrive at our body temperature of 37.5°C, but it also means that the 20°C at which we keep our homes and libraries is ideal for mould growth. Fortunately, most moulds also need biologically available water to survive, and we can keep mould at bay by keeping our things dry. (Humans had discovered long ago that drying or salting food preserves it by stripping away biologically available water.)
Mould growth happens when these three components come together:
- spores
- organic material
- water
Spores are everywhere, especially in household dust. Organic material is everywhere. The one factor that we can control is the availability of moisture. Most of the time, we have a pretty good handle on humidity; the problem is if we have a flooding event. In very old buildings constructed with lath and plaster, the lime in the plaster does a good job of fending off fungi. Most modern buildings, however, are made with drywall, which, as Bartlett says, “happens to be fungi heaven.” The core is a mix of calcium sulphate and cornstarch, which acts as a water wick. When we have a flood, we may forget that the moisture has gone up the wall well past the flood’s water level.
So what kinds of health effects can moulds have on people?
The structural components of the fungi, including the spores and hyphal fragments, have antigens that can trigger allergic reactions. Fungi also produce immunomodulating beta-glucans. Mixed organic dust, including fungal spores, can cause a condition known as organic dust toxic syndrome, which manifests as flu-like symptoms as your body tries to deal with all of the antigens. Enzymes produced by the moulds can trigger baker’s asthma, an amylase sensitivity.
If moulds are actively growing, they can produce mycotoxins and volatile organic compounds (responsible for the “mouldy smell”), which can cause irritation and may be partly responsible for sick building syndrome.
Because of these risks, people cleaning up moulds in a highly contaminated environment should take precautions, including a Tyvek suit that minimizes dermal contact (some mycotoxins are dermal toxins) with a fitted respirator to protect mucous membranes. In the case of flood, organic materials need to be dried out or freeze-dried within forty-eight hours, which isn’t always possible if the flood has also knocked out electricity. When the material is dry, control the relative humidity to below 40 per cent, increase air exchange rate, and clean materials with a HEPA-filtered vacuum. Bartlett cautioned that even if the microbes are no longer alive, the antigens they had produced may persist.
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Inherent vice: internal attributes of objects requiring conservation
External factors, such as temperature, moisture, and mould, can threaten our collections, but another problem is the natural tendency of some materials to self-destruct. Anne Lama, who worked for a decade in preventive conservation at the French National Archives in Paris, is now UBC Library’s conservator, and she spoke about the effects of this inherent vice.
Restoring books is a complex endeavour, explained Lama, because they have so many components: paper, glue, cloth, and sometimes leather or plastic. Most of the book is composed of organic materials, usually long strands of polymers. The longer these polymers are, the strong they are. The polymers tend to fold onto themselves and form covalent bonds, linking one strand to another. Where there are many of these bonds, the fibres have a more crystalline structure, which lends the material strength. Areas with fewer bonds are more amorphous, which gives the material flexibility. However, those amorphous regions are most vulnerable to damage.
For paper, the biggest threat is acidification. Some paper is inherently acidic: newsprint, for example, gets yellow and brittle very quickly. But even paper that starts out neutral can acidify over time as a result of oxidation. Using paper buffered to a pH of 8 or 9 can help counteract those effects. Conservators will sometimes put thin sheets of buffered paper between the pages of a book.
Sizing—starch or gelatin—on paper can react with light and lead to yellowing. After the nineteenth century, alum was a common sizing agent, but it is acidic and essentially impossible to stabilize. Inks used on documents are also a consideration: very old inks, made with carbon and gum arabic, are very stable. Iron gall inks, however, which were in standard use between the fifth and the mid-twentieth centuries, are very acidic; in some old books, the inks have chewed through the paper, and you can recognize letters in the text as holes in the page. Dye-based inks replaced iron gall inks about seventy years ago. These inks are not acidic but may be water soluble; even moisture in the air can cause a loss of contrast between the ink and the paper.
Parchment, which gets an alkaline treatment and is stretched on a frame to dry, is quite stable, although it is vulnerable to moisture. Leather gets a tannin treatment, which makes it more resistant to microorganisms but is acidic. Because of its low pH, leather is vulnerable to red rot, which turns the material to powder. That damage is irreversible.
Conservators may dip pages in a water or calcium carbonate bath to remove some of the acidity in paper. The water bath may also help restore some of the covalent bonds in the paper. To patch holes in paper, conservators can use a filling and repair lacuna, which has a suction table to draw pulp to the holes. Powdered resins and erasers are helpful in cleaning dust—not just surface dust but also dust within the pages. Parchment can be stabilized in a humidity dome, which allows the conservator to gradually increase the humidity until it’s at the desired level.
Conservators have to play a delicate balancing act: on one hand, they try to keep as much of the original item as possible. On the other hand, they need to intervene to prevent damage. Their intervention has to be at once discreet and obvious: they should do their best to use similar materials and techniques as the original to repair damage but also make the repair evident so that it’s clear the object has been restored. They have to use judgement in deciding how much of the patina to leave. Patina gives the object historical value, and you don’t necessarily want to get rid of it.