As cellulosic textiles age, hydroxyl groups (-OH) are converted to carbonyl groups (=O), which contribute to a dingy brown or yellow color. The chemical process known as reduction adds electrons to the cellulose fibers, stabilizing their molecular weight and returning carbonyl groups back to colorless hydroxyl groups. The combination of dissolved soils and cellulosic degradation often turn the wash bath the color of strong tea. The reaction of the sodium borohydride with water is also produces hydrogen gas bubbles, and the bath may give off a smell reminiscent of sulfur or chlorine. It is important to agitate the wash bath regularly to allow all sides of the textile to come in contact with the surface of the water where the chemical reaction is taking place.
If you are a textile conservator with experience in wet cleaning and bleaching historic artifacts, you may be interested in our MTS Handout, Bleaching Textiles with Sodium Borohydride, available on the MTS website.
The votes are tallied and our readers' favorite textile from 2014 is the Presidential coverlet! There is no mistaking its symbolism, importance or date. What we discovered as we began our research, however, was just how unusual this textile is in many ways.
By Jen Nason and Camille Myers Breeze
One of the procedures regularly practiced at Museum Textile Services is the science of wetcleaning. We use the term “science” because it truly is just that.
Many textile conservation labs like Museum Textile Services use a deionized water system. Although water alone is a strong cleaning agent, we may also employ a mild surfactant (similar to soap) to encourage additional soil removal. Occasionally we will also use bleach to improve the appearance of discolored textiles.
The favorite method of bleaching at MTS employs the reductive bleaching agent sodium borohydride (NaBH4). Other methods, such as chlorine bleaching, are oxidative processes. Sodium borohydride can only be used on cellulosic fibers, such as cotton and linen, because it is very alkaline and can damage naturally acidic fibers like wool and silk.
As cellulose ages, hydroxyl groups (-OH) are converted to carbonyl groups (=O), which contribute to a dingy brown or yellow color. Reduction adds electrons to the cellulose, which stabilizes its molecular weight and returns carbonyl groups back to colorless hydroxyl groups. Stains are not generally removed with the addition of sodium borohydride but the overall results are better than wetcleaning with surfactant alone. Remarkably, sodium borohydride is color safe when used at its proper strength, and MTS has safely bleached many embroideries, patchwork quilts, and other colored cellulose textiles
Whether or not you appreciate the science behind conservation, the results of our recent sodium borohydride treatments are quite impressive. The textiles seen here are noticeably brighter without looking over-cleaned. Most importantly, their preservation levels have been improved with a minimum of risk.
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