Here's a new word for everyone:
"foxing"
preservationists use it to describe the brown stains you see on old paper.
They are still not sure of it's cause...Most seem to say it's fungal. But it could be due to iron oxide.
There have been many studies
here's one link You are not allowed to view links.
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Loginwith some background info (there are many other studies, including with SEM)
I believe the brown stains we see on the Ingram money can be called "foxing" and might yield info ..i.e. how long does it take for foxing to appear on currency.
I was musing that the size of the mildew holes might also provide info about age (for instance, in a constant humidity environment, do the holes grow until the bill is fully consumed, or do other factors stop the mildew growth, once started?)
from that link on foxing
Factors favoring growth and/or color formation
Relative Humidity (RH)
There is no minimum degree of RH for growth of all fungi as the level varies not only with the genus but with the species as well (Beckwith et al. 1940, 311-313). The more hygroscopic the material (i.e. paper vs. leather) the lower the room RH can be in order to permit microbial growth (Gallo 1963, 59). It is important to remember that a micro-climate, vastly different from the overall room RH, can exist within the paper's structure. Unsized tissues, for example, interleaved into books may absorb and retain water over a long period of time creating localized high humidity relative to atmosphere; this could enable fungus to develop even when surrounding RH is below 75%. Fungal hyphae may transport water from higher to lower areas of RH, perhaps centimeters away [RK].
Most research directed at microbial growth on paper shows that below 70-75% RH the chances of growth for many "paper-attacking species" of fungi is low. Arai found that below 75% RH, germination of mold spores of the type isolated from foxed spots is unlikely to occur. Interestingly Arai also found that 84% relative humidity induced growth better than 94% RH, though this is specific to the particular fungi he isolated (Arai et al. 1990, 805). Beckwith et al. also found that below 75% they could not produce any fungal growth with the particular species they cultured (Beckwith et al. 1940, 313). In contrast to this, Nol et al. found three strains, previously isolated from foxed spots, which grew at 55% to 93.5-96% RH. Two of these strains also grew at 32.5% RH. However, foxing or coloration occurred only with one strain under RH conditions ranging from 32.5% to 96% (Nol et al. 1983, 24). Corte, Ferroni, et al in 2003 note collection environments should stay in the range of 40-60% RH to best avoid development of microorganisms and presentation of foxing marks ( Corte, Ferroni, et al. 2003, 172).
Temperature
Each species has its optimum temperature for growth. Generally, it has been found that growth increases with increasing temperature and decreases with decreasing temperature. Excessive heat kills most fungi and steam is a standard means of sterilizing cultures in lab procedures.
pH
All research has shown that foxing stains are more acidic than the surrounding paper (see, for example, Arai 1980; Hey 1983; Iiams and Beckwith 1935).
Arai's research suggests that the presence of amino acids is necessary when inducing foxing and that increasing the concentration the of amino acids results in darker brown spots (Arai et al. 1990).
Nutrients
Fungi may find nutrients in one or more of the following.
Cellulose
While some researchers insist that cellulose is not damaged in foxed areas (Meynell and Newsam 1979, 567), others have shown conclusively that fungi digest the cellulose (Cain 1983, 16 and Nol et al. 1983, 23).
Sizings and Adhesives
Because they saw no damage to fibers, Meynell and Newsam claim foxing feeds on gelatin size, not on the cellulose (Meynell and Newsam 1978, 467). However, observations have also been made that fungi prefer more hygroscopic, unsized papers to those that are sized (Meynell and Newsam 1978, 468; Gallo 1963, 58).
Investigation into the influence of fillers and sizes on fungal growth and its production of acids found the following: gelatin, starch and dextrins promoted growth and color production (Beckwith et al. 1940, 3307). There was less acid production by fungi feeding on casein and rosin than with starch or cellulose alone.
Oils
Either from the medium of printing ink in a text or that transferred to paper by readers' or handlers' hands (Meynell and Newsam 1978, 467).
Micro-dust
Light Intensity
Generally, the growth rates for most fungi are not sensitive to light intensity. However, no study has been made of the relationship of foxing stains to light.
"Examination of a 1896 thirty-four volume set of Balzac's works on laid cotton paper found 'snowflake' fungal foxing in circulated volumes no different from that present in 1896 uncirculated, unopened volumes. Previously uncut pages were slit in the dark and examined in the first light exposure in nearly ninety years. Apparently dark storage produced the same pattern, color, and frequency of foxing as occasional exposure to light (Cain, Stanley and Roberts 1987, 24).
Metal-Induced Degradation
"Cellulose is directly oxidized catalytically in the presence of iron, copper, and cobalt compounds, and the reaction is most rapid at high humidities" (Tang 1978, 19). Metal impurities in paper, specifically iron and copper, are believed to result from particles abraded from the metal equipment and/or from contaminated water used in the papermaking process. Additionally, all wood-pulp paper may be expected to contain iron, as it is naturally present in wood (Beckwith et al. 1940, 302).
"In 'bullseye' copper-or iron-induced foxing the role of these two metals is probably that of oxidative catalyst. Both metals can undergo reversible oxidation-reduction. For example, they are both found playing such a role in metabolic biochemical reactions. Iron can alternately be oxidized from the +2 (ferrous) state to the +3 (ferric) state and then be reduced back to the +2 state as it plays the role of oxidizer. Copper can do the same between the +1 and +2 states. Thin-layer chromatographic studies show the extracts of 'bullseye' foxed and unfoxed paper to have all or most of the same bands. This further suggests iron and copper act to catalyze (accelerate) the oxidative degradation of paper" (Cain 1983, 15; Cain and Kalasinski 1987, 57). In a tally of metal-induced foxing, analysis showed that twenty-seven were induced by copper and copper alloys to over 200 induced by iron (Cain and Miller 1982, 7).
Iron
Coloration
"The very color of foxing connotes the presence of iron" (Iiams and Beckwith 1935, 412). Iron ions create yellow-brown spots and Tang found that "there is a trend for darkness of the foxing spot to increase with increasing iron content; the highest concentration of iron was noted in the center of the spots, with the metal concentration decreasing... as the distance increased from the center" (Tang 1978, 24, 26).
Occurrence
It would be very difficult to find any paper without some degree of iron [MH]. Numerous researchers have identified iron ions within foxing stains and found a significantly greater concentration of iron in the foxed areas compared to surrounding paper (Cain 1983, Cain 1988, Cain and Miller 1982, Cain and Miller 1984, Daniels 1988, Gallo and Hey 1988, Tang 1978, Tang and Troyer 1981). One study, however, found no difference between foxed and unfoxed areas (Press 1976, 29). This was corroborated by Tang, who found that in some foxed papers there was no difference in iron (or other metal ion) concentration (Tang 1978, 28). While concentrations greater than 500 ppm have been identified with undesirable spots, Hey suggests that "if iron is involved it is not its total concentration that is important but rather its availability to participate in reactions or its effective solubility" (Tang 1978, 28; Hey 1983, 341).
Form
Research indicates that iron in paper is found entirely in the ferric, rather than ferrous, form (Beckwith et al. 1940, 303).
Activation
Iron will not corrode below 70% RH, but in the presence of ions such as chloride, storage needs to be at 40% RH or lower to avoid corrosion. Hey suggests that "there is a strong chemical possibility that heavy metals present in the paper in a quiescent state will be activated by washing with an acid water, when this is not followed by deacidification" (Hey 1979, 68).
Copper
Daniels and Meeks describe copper-related foxing as varying in size "from small spots with no apparent nucleus and only a brown diffuse discolouration, to large spots of about 5 mm diameter with black dendritic patterns or green corrosion products; these spots include an outer ring of brown discoloured paper" (Daniels and Meeks, n.d., 2). Analysis by EDX revealed that the foxed areas contained copper, zinc, sulfur, and chlorine, while the unfoxed areas "did not have detectable amounts of these elements" (Daniels and Meeks, n.d., 5); see Spot Tests. It was concluded that chloride ions, from original or subsequent bleaching residues, accelerated the corrosion of brass (a copper/zinc alloy) inclusions in the paper. The soluble copper compound was then able to react with hydrogen sulfide generated in the paper or absorbed from the atmosphere. The stain was due to a combination of black copper sulfide and brown copper catalyzed degraded cellulose (Daniels and Meeks, n.d.,
. Tang linked copper concentrations greater than 50 ppm with formation of undesirable spots (Tang 1978, 28).
Condensation
A modification of the cellulose, often visually evident by browning, which takes place at the interface between wet and dry parts of fibrous materials and which is not the result of degradation products being carried and deposited by a spreading liquid. "Experiments suggest that the interaction of air, water and cellulose is responsible for the formation of browning" (Hutchins 1983, 58). This interaction could occur at sites of temporary moisture accumulation in the paper. "Depending on the moisture content of a book, [for example,] it would be possible for uniform discolouration of zones, as well as smaller or larger stains, to develop. All the possible factors that influence condensation and evaporation would play a role in this: humidity, temperature, air pressure, paper porosity, and any irregularities in the paper which could include folds, tears, and dirt particles; even the presence of concentrations of iron or fungus could likewise induce condensation" (Ligterink et al. 1991, 51).
The above authors speculate on the relationship between foxing and other forms of discoloration (text block areas, leaf margins). The link is based on observations of both types of staining (foxing and zonal) appearing together on the same page in many books.
The condensation explanation for browning is a broad view ascribing moisture and cellulose and possibly oxygen as the only necessary ingredients to achieve staining. The presence of fungi and/or metals would act only as attractive sites for moisture and consequent browning.
Multiple Causes
Given the ubiquitous nature of both iron and fungi in paper it is quite possible they often act in tandem. Research appears divided (fungal infection vs. metal-induced degradation), and one must keep in mind, when reviewing each study, whether the presence of a dual cause was fully investigated. Often researchers did not adequately test for iron when they found fungi and vice versa.
A good example of this is the use of the SEM. Where Cain and Miller did not, in one study, find an iron core using SEM and EDX, they successfully located it using narrow beam x-ray fluorescence (see Analytic Instrumentation). Other research, however, has relied on SEM alone to determine that there was no iron (or other metals) present without using other methods to check their results.
As early as 1935, Iiams and Beckwith proposed a dual cause of spot formation: organic acids secreted by the metabolizing fungi react with iron present (even in trace amounts) in the paper to form unstable organic iron salts (organo-ferro compounds) which decompose to form iron oxides and hydroxides i.e. brown/rust coloration (Iiams and Beckwith 1935, 414).
Iiams and Beckwith also found that adding a 1:1,000 solution of iron caused fungal growth which "greatly exceeded any that had been produced in the laboratory without the presence of iron in the culture papers" (Iiams and Beckwith 1935, 414). Their later research confirmed this as well as showing that iron increases the degree and intensity of the discoloration which accompanies fungal proliferation (Beckwith et al. 1940, 303-306). The resulting brown tint had the color of ferric oxide. The presence of casein, gelatin, and starch add to the discoloring effects of iron.
Hey concurred with Iiams and Beckwith and proposed these dual mechanisms:
1. damp -> mold acid -> activation of iron -> increased acid -> mold death
2. damp -> activation of iron -> increased acidity -> local encouragement of mold -> increased acidity -> death of mold [Hey 1983, 341]
These models suggest that one reason why foxing stains do not cover an entire page might be that the acids secreted by the fungi collect, eventually reducing the pH enough to curtail further fungal growth.
Cain and Miller found that "snowflake" foxing contained a higher iron concentration than the surrounding paper (Cain and Miller 1982, 61). A later study found hyphae and occasional fruiting bodies in all snowflake fungal foxed areas examined (Cain, Stanley and Roberts 1987, 24). This suggests a dual cause.
Fungi use iron and copper as co-enzymes. This means that they are essential elements. After use, the excess may be secreted (perhaps as an altered or activated ion) [RK].
Origin/Occurrence
Related to the Manufacture of Paper
The extent of foxing appears to be in direct proportion to methods used in the manufacture of paper (Iiams and Beckwith 1935, 413). It is possible that the potential for foxing is created when the sheet is first made - the foxing only becomes visible later when storage conditions encourage it. Factors include the poor preparation of fibers, impurities in the pulp and the water added to it, and poor bleaching with chlorine. On the other hand, papers manufactured with a high magnesium or calcium carbonate content are less likely to be foxed. It has also been noted that woolen or rayon felts are damaged continually by microbial attack as shown by Sharpely and King. Two species of fungi located in damaged felt fibers are Aspergillus niger and Aspergillus fumigatus, both associated with foxing and noted for their cellulolytic capabilities [EM].
Causes Related to Storage
Ligterink et al. proved that foxing stains found in one particular book arose during storage of the loose sheets prior to binding. They noted that the stain patterns which were not repeated on an adjacent page were sometimes repeated on another page later in the book. By reconstructing the original unfolded, uncut quires it was discovered "that the stain patterns of successive quires matched up if the unfolded sheets were laid on top of each other, and could often be followed down through many sheets in the stack. The storage of these unfolded sheets obviously determined the form of the stains observed which must have therefore arisen before binding" (Literink et al. 1991, 49). Interestingly, the stains were probably not visible at the time of binding as the discolorations are so great in some sheets they would probably have been discarded by the binder (see also Printing Papers). By the same reasoning, book papers which show the same foxing pattern through several adjacent pages indicate the foxing began and became visible after the pages were bound.
Causes Related to Dampness
Research indicates that the internal moisture content of the paper must be at least 10% for fungal growth to occur (Allsop 1985, 59). At 80% RH, paper in general absorbs 9-14% water, with more hygroscopic paper, a lower RH will permit mold growth. Iron alone will not corrode below 70% RH but in the presence of ions such as chloride, papers must be stored at 40% RH or lower to avoid iron corrosion.
Poll