We have been bleaching and wet cleaning a variety of textiles this spring at Museum Textile Services, including christening gowns, wedding gowns, coverlets, lace, and embroideries. Our favorite method employs the reductive bleaching agent sodium borohydride (NaBH4). Wetcleaning cotton and linen fibers with the addition of a sodium borohydride bath is beneficial both visually and chemically, resulting in healthier and brighter artifacts. Sodium borohydride cannot be used on protein fibers—such as silk and wool—because they are naturally acidic and the sodium borohydride solution is alkaline (approximately pH 10).
Remarkably, sodium borohydride is a color safe way to bleach cellulosic textiles. Along with many white coverlets and quilts, we have bleached embroideries and samplers that have a linen or cotton ground and multi colored cotton thread. First, we test the color fastness of the colored threads. If there is dye bleed, the object is not a good candidate for full immersion wet cleaning. We have also had success bleaching a white rayon wedding dress from 1947. Rayon is a synthetically produced cellulosic fiber with a naturally high pH just like cotton, linen, and other plant fibers.