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.
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.
by Camille Myers Breeze
In January, 2011, Mary O'Dwyer brought us her grandfather's 1875 christening gown, to see if we could do anything to help her. We could not believe our eyes when she arrived with a pair of lovely cotton garments the color of robin's eggs. The blue was streaky and could not mask a pattern of brown stains, most noticeable on the front.
Although most of us had heard the term "bluing" we had never seen a dramatic example in person of what could go wrong with the treatment. The principal behind bluing is that the yellowing that occurs with aging in both natural and synthetic fabrics can be neutralized with the addition of a light application of blue dye. This same principal is used by some older women on their hair, with infamous results. The active ingredient in bluing is a fine iron powder containing the pigment Prussian blue (ferric hexacyanoferrate). Several brands of laundry bluing were popular from the late 1800s, including Mrs. Stewart's, which is still sold today.
While Mary O'Dwyer was still in our studio, we pulled an old book from our library shelves and read up on laundry bluing. Laundering and Dry Cleaning, published in 1925 by the Women's Institute of Domestic Arts & Sciences, Scranton, PA, gave the following advice for bluing in section 81:
This same book states that, "If it does happen that the clothes become overblued, they may be whitened by placing them in cold water and heating them to the boiling point, repeating the process if necessary until all excess bluing is removed." However, similar attempts had already been made without success. An online source gave additional advice to "use a solution of 1 C. household ammonia to 1 qt. of cold water and soak, covered tightly for 48-72 hours. You may need to perform this procedure 2-3 times, washing with detergent following each process."
Mary O'Dwyer decided to try the treatment herself, with some trepidation. Imagine our delight the following summer when out of the blue she emailed us these photos of her family christening gown, clean and white! She reported that her granddaughter had been baptized the previous Sunday and that the dress looked beautiful. The simple ammonia soak was successful in reversing the bluing and did not leave the cotton dry or brittle.
Although we still have no first-hand experience treating blued textiles, we're delighted at the success of this old-school recipe.