3 SELECTION OF MATERIALS

IN RECOGNITION of the fact that conservators will want to fumigate a very wide variety of materials, attempts were made to obtain many different types of paper and textiles. The criteria used in the initial collection of sample material were as follows:

1. availability of at least 100 g of fiber
2. absence of components that may greatly interfere with analysis of samples or interpretation of results (e.g., dyes on textiles, coatings on paper)
3. absence of large quantities of dirt, grime, etc.
4. a reasonably homogeneous appearance
5. ability to be dated
6. cost (for those materials purchased from dealers, secondhand stores, etc.)
7. the likelihood of appearance in museum collections with reasonable frequency.

More than 60 different types of paper and textiles were gathered. They were screened for obvious signs of similarity and lack of relevance to museum collections. The remaining 43 fiber types (see tables 1, 2) were subjected to a series of analyses that characterized the material further, thus permitting a more informed selection of the materials to be included in the investigation.

TABLE 1 Paper Samples Initially Characterized

TABLE 2 Textile Samples Initially Characterized

The analyses performed included:

1. spot test for starch size (Browning 1977, 90–91)
2. spot test for gelatin size (Browning 1977, 102–3)
3. spot test for lignin (Browning 1977, 72–73)
4. estimation of average degree of polymerization by viscometry (described in section 4).

Attempts were made initially to test papers for the presence of alum/rosin size through spot tests for rosin (Browning 1977, 78–87). However, the results of procedures currently available were difficult to interpret. Other methods were considered (e.g., atomic absorption, X-ray fluorescence) but were judged to be too time consuming for a simple characterization study.

After study of the characterization data, 23 papers and textiles were chosen for the investigation. The selection was based on the need to obtain a series of fibers that represents a wide range of ages, degrees of degradation, and concentrations of lignin (from barely detectable to heavily lignified). Attempts were also made to include samples that contain sizing material typical of their period (especially important for paper).

Obtaining suitable naturally aged materials was one of the greatest difficulties encountered in collecting materials for the project. In particular, we experienced problems finding authentic pre-Victorian textiles in quantities sufficient for the study. However, it was considered important to make every effort in this direction so that our data can be more confidently applied to the naturally aged artifacts that predominate in most museum collections. It is likely that naturally aged fibers will not be affected by Vikane fumigation in the same way as modern paper and textiles. To give conservators comprehensive guidelines, we needed to study both “old” and “new.”

The second most important variable in selecting material was the degree of degradation. This is a significant point, as the range of degrees of degradation should approximate those found in museum collections so that the results are applicable to museum collections. It is highly likely that the state of oxidation of a fiber, the presence of acidic material, and degree of crystallinity will greatly influence the chemical and physical interaction of sulphuryl fluoride and the fibers. From the point of view of the characterization and screening process, the estimation of average degree of polymerization (as calculated from intrinsic viscosity [η]i); lignin content (degradation tends to increase as lignin content goes up); and visual inspection for color change are most helpful in giving some estimate of the degree of degradation.

The presence of a size in paper and textiles could be a significant factor in determining the effect of sulphuryl fluoride on the fibers. Size affects the porosity of the artifact and thus absorption of the fumigant into the substrate. The type of size may also be a consideration, especially if it reacts with Vikane. The size most likely to react with sulphuryl fluoride is gelatin, a collagenous-based material commonly found in 18th- and 19th-century papers (Hunter 1978). The interaction between proteins and Vikane to form N-fluorosulphonyl derivatives (Meikle 1964) or undefined products (Osbrink et al. 1988) has been documented.

Deacidification buffering salts such as magnesium or calcium carbonate or zinc oxide could also influence the uptake and reactions of sulphuryl fluoride with cellulosic and ligneous fibers. Those buffering chemicals with an alkaline pH may promote the hydrolysis of the fumigant and may affect the quantity of fumigant reaction products that becomes associated with the samples after hydrolysis.

All of the above points concerning the possible effect of proteinaceous sizes and deacidification buffer salts pertain mainly to paper samples. Therefore, it was considered valid to limit experiments that specifically explore these questions to paper samples. A plan was developed to treat one paper, a ledger dated 1897 (paper 12) by an exhaustive washing procedure followed by sizing with 2% gelatin (paper 12B) or deacidification with magnesium bicarbonate at a concentration of 7.6 mg/ml (paper 12C).

These three experimental papers are listed in table 3, along with the 10 other papers chosen for the investigation. The 12 experimental textiles chosen are given in table 4. Altogether, 25 different paper and textile fibers were used in the project. Wheat starch in the form of dry powder as well as films cast from cooked starch was also included at the request of conservators (Weidner 1987).

TABLE 3 Initial Characterization of Paper Samples Selected for Study

TABLE 4 Initial Characterization of Textile Samples Selected for Study

Tables 1–4 contain the characterization data used in the final selection process. The age of the samples vary from 1622 to modern; the DP�s range from below 250 (aged groundwood papers) to more than 1,770; the lignin content is anywhere from zero to extremely lignified (jute textile and groundwood papers); the quantity and type of size varies with the type of processing a fiber has been subjected to, the age of the sample, and its past history.