Comparison of Cleaning Treatments for Conservation and Restoration of Cotton, Wool and Silk Fabrics

Cleaning ensures sanitization and thus the safety of the artefact itself and others stored/displayed in its vicinity. At the same time, the process invariably alters the character of textile to a certain extent. Cleaning ensures removal/deactivation of soil and harmful organic matter from the artefact. However, a small number of surface molecules from the textile might be eroded in the process as well. 

This leads to weakening of the textile and might cause alteration in colour spectrum/ depth etc. Controlled cleaning techniques in conservation laboratories focus on minimizing this damage. However, not much scientific data is available on the efficacy of present cleaning techniques employed in conservation laboratories. Presently aqueous cleaning and solvent cleaning are primary modes utilised as next step to dry tools. Additionally, novel cleaning technologies like enzyme wash and ultrasonic wash provide soil specific methodology that would reduce the threat to the base fabric.

The present paper is a systematic analysis of these cleaning techniques and their impact on aged museum fabrics, i.e., cotton, wool and silk. Change in tensile strength parameters, whiteness index and yellowness index have been used as indicators to test the efficacy of different cleaning techniques on aged museum textiles. Numerical data generated by laboratory experiments clearly indicate that there is no standard cleaning treatment available for the three natural fibres. Each fibre has exhibited suitability to different cleaning treatment while balancing between restored whiteness and minimizing strength loss.

INTRODUCTION

Cleaning is an important part of conservation and restoration. Cleaning of historic textiles is an essential step which not only helps to prolong the life of the textile but also eradicates the decaying material to some extent (Naithani & Kharbade, 1987). An unsanitized artefact doesn’t only pose a hazard to its own longevity, it also becomes a potential threat for artefacts stored or displayed around it. At the same time, cleaning is also one of the most complicated tasks in the conservation laboratory. Invariably, the artefact is at risk of alteration in structural and functional properties, as an after-effect of cleaning.

As Per Balazsy, 2006, ‘A large part of the weight decrease of cellulose on washing originates from the elimination of the lower molecular weight water-soluble deterioration products. The washing of highly degraded cellulosic textiles should be considered with great caution because the elimination of too many deterioration products may cause disintegration of the textile ‘. Older the artefact, higher is the risk. Again, the impact is different for different fibres. Thus, it is very important to ascertain, various possibilities for safe cleaning of aged textiles, keeping in mind change in strength and visual parameters.

Traditionally, conservation laboratories have been largely dependent on surface cleaning through vacuuming and other dry techniques. Occasionally, wet cleaning with laboratory reagents is used, after ensuring the strength parameters of the artefact. Dry-cleaning/ solvent cleaning has been another common approach for sanitizing museum textiles. Recently, enzymes have been making their presence felt in these laboratories. Ultrasonic cleaning techniques are also supplementing options for conservators.

However, the lack of experimental data about the efficacy of any of these techniques and their impact on fabric strength discourages museum workers from making confident choices about the same. As noted by Brooks, 2006, ‘Categorical distinctions between clean and dirty are not fixed but are culturally defined, which means they alter over time, space and context. Perceptions of cleanliness are therefore not absolute’. Any cleaning treatment in conservation laboratory has to balance between the loss in strength and cleaning perceptions.

The objective of this study is to test the efficacy of all these cleaning techniques in restoring whiteness of artificially aged fabrics made in cotton, wool and silk. Also, change in strength parameters have been numerically established, so that conservation laboratories can make an informed choice about methods available for cleaning and restoration purposes.

METHODOLOGY

Cotton, wool and silk samples were selected for research. The samples were tested for determination of tensile strength and Whiteness Index and yellowness index. Samples were subjected to accelerated ageing as per the method suggested in the AATCC Test Method 26-1994. This ascertained that samples were brought to a condition of approximately 20years of ageing. Aged Cotton, Wool and Silk samples were taken for Tensile Strength testing and Spectroscopy. Standard testing procedures were followed to measure the indicators. Thereafter, the aforesaid samples were divided into 4 groups for wet cleaning i.e., home laundry, enzymatic cleaning, dry cleaning and ultrasonic cleaning. The samples were subjected to treatments as appropriate for their fibre content. For example in the home laundry group cotton was exposed to the detergent, temperature and conditions prescribed for selected fabrics. After wet treatment, the samples were again tested for loss in tensile strength and removal of yellowness. Recorded values for whiteness Index and tensile strength were then compared to determine the best possible method.

A Home Laundry

Home laundry techniques are probably the oldest and simplest means of sanitizing fabrics. The primary merit of this method is that the worker gets to closely interact with fabric at every stage of treatment. This ensures the possibility of simultaneous improvisation, while the fabric is still under treatment. A crucial advantage of this technique stands that professionals can modify the procedure as per suitability to the textile while retaining absolute control over the artefact at the same time. For the purpose of this study AATCC test method 61-2007 was followed. Test no 1A- was used as specimens subjected to this test should show colour change similar to that produced by five typical careful hand launderings at a temperature of 40+/-30C. Laundering machine was adjusted to maintain the designated bath temperature of 40+/-20C. The wash liquor was prepared with total liquor volume of 200ml and detergent concentration at 0.37%. The test was run in lever lock stainless steel canisters of size 75X125 mm with 10 steel balls in each canister. The laundering machine was run for 45mins after which each test specimen was rinsed in a separate beaker. Each specimen was rinsed three times in distilled water at 40+/-20C with occasional stirring and hand squeezing. To remove excess water, flat specimens were pressed between folds of blotting paper. Thereafter, specimens were air-dried, placed flat on a blotting paper. A commercial detergent was used for cotton fabrics whereas a neutral soap was used as ‘non-ionic’ detergent for wool and silk.

Dry Cleaning/ Solvent Cleaning

A synonym of solvent cleaning, this technique has been widely used for cleaning of sensitive textiles like wool, silk, chiffons. Most sensitive fabrics that behave adversely to aqueous medium stand comfortable to dry cleaning. For the purpose of this research AATCC test method, 158-1995 was used where samples were dry-cleaned at a commercial workshop with perchloroethylene. Drycleaning machine with a commercial rotating cage was used. The sample fabric was placed in the machine and perchloroethylene was introduced. The machine was run for the specified period of time. The solvent was thereafter drained and centrifuged. The load was dried in a drying tumbler by circulating in warm air for an appropriate time. The specimens were removed from machine immediately and placed on a flat surface for drying.

Enzymatic Cleaning

Literature about the use of enzymes is available from the late ’60s. In 1988, Segal published a paper reporting important factors affecting enzyme activity and various immersion and non-immersion techniques of application. Contemporary studies have repeatedly noted the efficiency of Cellulase enzyme as an effective bio-polishing agent for cotton fabric which considerably preserves the strength and weight parameters of the fabric in contrast to other chemical techniques (Bhat, 2000). The primary advantage of using enzymes is that enzymes are substrate-specific. Thus if proven useful, they stand superior to all parallel techniques of achieving a desirable result. The concept utilized in this section of the study is that of bio-polishing. The phenomenon talks about removing the damaged superficial layer of the fabric and restoring the fresher subsequent layers (Doshi et. al, 2001). Since the fabrics used in this section of the research were both cellulosic and protein in nature Cellulases and Proteases were the enzymes used for the purpose.

CONCLUSIONS

Thus it can be seen that no one method, in general, can be considered suitable for cleaning of aged fabrics made from different fibres. Enzymatic cleaning by Cellulase enzyme has been proved to be the least harmful and most efficient method of cleaning aged textiles. Therefore, Enzyme wash in aged cotton fabrics is the most balanced method of sanitization without much loss of strength and performance parameters. However, in the case of wool fabric; home laundry, dry cleaning and enzymatic cleaning by protease enzyme prove equally beneficial in cleaning the fabric with minimum strength loss. This can be attributed to the inherent nature of the wool fabric to resist damage due to deterioration. On the other hand, ultrasonic wash at 5 minutes presents the most suitable cleaning option for silk fabric. The findings of this section confirm that fibre constitution has a profound role in deciding suitable cleaning treatments for aged fabrics.