Nov. 23, 1998 "Darling, if you really love me, please, clothe me in the colors of precious metals" is a quotation that strikes the heart of Dr. William Todd, and well it should.
Todd, a researcher in the Department of Veterinary Science at the Louisiana State University Agricultural Center, has developed a method for dyeing fabrics with precious metals -- and at an affordable cost.
It may not be long before people are wearing clothes colored with precious metals if the microbiologist has anything to say about it.
The process, which Todd developed along with Nell Morris, an Ag Center research associate, from their experience in biomedical research, uses minuscule amounts of metals -- particularly precious metals such as gold -- to infuse colors in a host of fabrics.
"Gold colloids are used in biomedical research and clinical diagnostics as sensitive signals to detect the presence of pathogens," Todd says. "These metal colloids are attached to antibodies for rapid diagnostic tests."
When working with diagnostic assays, Todd concluded the same properties that allow them to be used as diagnostic tools could also allow gold and other metals to be used as dyes.
So instead of putting these particles in solution for diagnosis, Todd found a way to put them into textiles for color.
"In nature, minerals are colorful," Todd says. "We found a way to put this color into fabrics."
The microbiologist uses a reagent to bond the metal particles deep into the textile fibers and make the metal actually a part of the chemistry of the filament. The chemicals of the fabric influence the color.
The actual hue is determined by a combination of the element itself, the size of the particle, the chemical nature of the particle and the interaction of the metal with the chemistry of the fabric.
"Essentially, you can use any metal," Todd says, explaining his first experiments were with gold and titanium because they're common in the medical laboratory where he developed the process.
The simple process begins by soaking a piece of fabric in distilled water and then in a reagent that creates "sites" in the fabric where the metallic ions will bond. The fabric then is soaked in a solution of the metal -- typically at 0.01 percent of the element or compound. Finally it's rinsed and dried.
The result is a colored fabric, and the color is permanent.
By using different elements, reagents, textiles and solvents, Todd can create a surprising range of reproducible colors and tones. "The chemistry of the fiber and its interaction with the reagent are of critical importance both to the character of the color and to the stability of the final product," he says.
For reagents, Todd uses such common materials as chlorine bleach, ethanol, distilled water, hydrochloric acid, hydrogen peroxide and tannic acid.
"The reagents reduce metallic ions, which are then formed into particles and grown," Todd explains. "By controlling their size, we can vary the color.
"The particles are so small they can't be seen with a microscope," he adds. "But they produce a bright signal with a very small amount of metal. And since metals can be combined into alloys, different combinations can produce a variety of colors."
In addition to the fabrics' chemical compositions, the nature of the colors also is affected by how the fibers are spun.
"We've demonstrated we can produce a wide range of attractive colors using filament and spun viscose yarn with only a few elements," Todd says. "With some elements, such as gold, it's easier to control the color by dyeing strands of yarn rather than woven fabrics.
"Because a strong color signal is produced by relatively few nanometer-sized particles, the method is realistic in cost, even with gold, " he adds. "We calculate that 1 ounce of gold will color about 380 miles of spun viscose yarn at a medium level of intensity. With some of the other elements, the cost is less than one penny per liter of the solution."
Colorfastness is another of the benefits of the metal dyes.
"Common organic dyes bleach out through the sun and chemicals," Todd explains. "Colors made by metals will remain forever."
To demonstrate the permanency of the process, Todd used delicate silk to show the effects of bleach. He soaked a swatch of cloth in undiluted chlorine bleach for 10 minutes, then rinsed it in water. The color of the gold-dyed silk remained.
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