Techniques for Pre Treating & Mordanting Linen

Lady Gwenhwyvar ingen Greig,

CVO, CMC, CGHM, CSP

Just as it was for our ancestors, the techniques for natural dyeing are a simple but lengthy process. With the advent of modern chemistry and our vast understanding of complex molecular science, we are now able to unravel this simple art of dyeing to reveal the mysteries of the complex chemical processes that have been in place for thousands of years. It is through these chemical processes that we find our explanation for the reasons that certain fibers take up pigments. It is the adjustment of pH within natural fibers that allow the dissolved pigments in natural dyestuffs to enhance and color fabrics.[i] This adjustment is achieved with the use of simple chemicals and metallic salts in the pre treatment and mordanting of these fibers.

Mordant is from the Latin word mordere, which means to “bite” or “fasten”. Concerning dyeing, mordanting conditions the fibers with the use of metallic salts and chemicals. This allows the cloth or yarn to accept the pigments from natural dyestuffs and encourages them to hold these pigments so they can accept color and remain fast.[ii] In simple terms, this is basically the chemical process of adjusting the pH of natural fibers for dyeing. While the application of pre treatments and mordants does affect the final color from the dye bath, we will simply concern ourselves here with the action of assisting the fibers to accept the pigments.

The Structure of Fiber

On the subject of dyeing linen, it is a common misconception that this fiber will not readily accept the pigments from natural dyestuffs. To better understand the necessary steps for dyeing linen, we must first gain a simple understanding of the structure of the plant fibers. Flax, the plant from which linen is derived, is a cellulose fiber. These long fine strands of cellulose are arranged in tightly bound plates with intersecting joints or nodes along the length.[iii] Each fiber is covered with a waxy outer coating. While the fiber arrangement and the waxy coating are what give linen its inherent strength and resiliency, they are also what create difficulties with colorfastness in the natural dyeing process and dictate the need for proper pre treating and mordanting.

Bundles of flax fibers viewed at 1:425 scale under an electron microscope. The nodes are visible as striations across the length of the fibers.

Pre Treating and Mordanting

The first step in the pre treatment and mordanting process of linen that must take place is the waxy outer coating must be softened so the mordant and later the color can adhere to the fibers. The easiest way to initiate this is by treating linen in boiling water to which washing soda or ammonia has been added. Washing soda is also known and marketed as sodium carbonate. This takes the pH to an extremely alkaline or high range. As our ancestors did, this pH adjustment process can also be achieved by using stale urine.[iv] These pre treatments are now known as assistants. The purpose of using a soda or ammonia assistant prior to mordanting is to increase the alkalinity and to improve absorption of the mordant which in turn increases colorfastness.[v] I generally add one half cup of assistant to every 2 gallons of water. You can purchase pH test strips from your local drug store to check the level. A good conditioning range is around pH9-pH10. Adjust the level by adding more assistant or water as needed.

Once the pH has been adjusted and the fabric conditioned, it can be rinsed and mordanted with alum or a combination of alum and tannic acid. Alum and tannic acid can be purchased form a druggist, compounding shop, and dyeing supplier. Tannic acid can be readily extracted from oak galls. Oak galls are produced when the gall wasp deposits her larva inside a small oak shoot. The larva encourages and stimulates the tree to grow plant tissue around the egg case resulting in small potato-like protuberances at the base of the tree. They can be harvested fresh and dried. The action of mordanting is to condition and aid the fabric in accepting the pigments and to adjust the pH to an acceptable range for dyeing after the pre-treatment phase is complete. An acceptable pH range for dyeing linen is around pH7.5-pH8. Please refer to a natural dyers guide for proper ratios of mordanting compounds to water. There are many different techniques for this process and many are based on a percentage of dry fabric weight to compound or either water volume per container. After proper mordanting, your linen can be dyed with most soluble natural pigments and will retain just as much color as other natural fabrics for quite some time if treated with care.

Colorfastness With Linen and Other Fibers

As with all natural pigments on natural fibers, light and wash fastness can be greatly enhanced by the use of proper mordants.[vi] However, linen poses an especially challenging problem in this area. Again we must look at the fiber structure to understand this complication. Due to the structural binding of the cellulose fibers in linen, the pigments will only adhere to the surface of the fibers. [vii] While linen will dye just as vibrant and deeply as other fibers, it will not retain its color as long. Fading is due not only to the fiber structure but to the delicate and fugitive nature of natural pigments to our environment. Exposure to air, light and chemicals speed the deterioration process. A good example of this is the pigments found in woad. The natural pigments in woad are a pale yellow to sherry brown color.[viii] It is the exposure to an alkaline bath, heat, and finally air that converts the pigments into their common blue. Laundering also leeches color from fabrics. While we basically have no control over most environmental factors, here are a few laundering tips I have discovered that can help all of your naturally dyed fabrics retain their color longer.

· Never use commercial laundry detergents. Use a pure soap such as Castile or Ivory flakes.

· Always use cold water that you have allowed to sit in the washer tub for 24 hours to evaporate the chlorine.

· Wash garments on gentle cycle to avoid stretching or breaking the fibers. This will cause them to release dye.

· Hang to dry and iron only when the garment is completely dry.

· Always hang naturally dyed linen garments. Folding can break the fibers causing them to release dye along fold lines when laundered.

Often times, reversing the pH can assist in setting the color. Check first to make sure your dye products is not pH sensitive. If they are, setting the color can change the outcome of your dye bath. For cellulose fibers dyed with non-pH sensitive pigments, finishing the dyeing process with a warm bath to which acetic acid, or common household vinegar has been added can do this. Heating the mixture slightly will further enhance the lifting of the waxy coating and allow the color to adhere more readily to the fibers. Leave cellulose fibers in the fixative for 5 minutes or less. Prolonged exposure to acids will harm the fiber structure. Afterwards, a plunge into a cold-water bath will help seal the color in.

Tips For Dyeing Linen and Other Cellulose Based Fibers

· Cellulose fibers dye more evenly when they mordant at room temperature for 12 to 24 hours. Start them out warm and let them sit.

· Make double or triple strength dye baths for linen and double the dyeing time.

· The normal pH of cellulose fiber is in the alkaline range. Taking the pH to a high or alkaline level will not harm the fibers, dropping it to a low or acid pH will cause brittleness and retard lack of color absorption. Expose to acids for only a short period of time.

· Always add fabric or fibers pre treats, mordants, and dye baths wet to ensure even distribution of the chemicals and color.

· Air dry after dyeing to ensure an even color set.

· Keep dye baths around the appropriate temperatures recommended for the pigments. Raising the temperature will alter resulting colors.

Bibliography

Rita Buchanan. The Dyer’s Garden. (Loveland, CO: Interweave Press, 1995)

Jenny Dean Wild Color. (New York, NY: Watson Guptill Pub. By Octopus Publishing Group Ltd., 1999)

K.G. Ponting Discovering Textile History and Design. (Aylesbury, Bucks, UK: Shire Publications, LTD. 1981: second edition reprint, 1986)

Jodi Smith. Medieval Dyes. (Spinning Madly: 1995)

Joyce Story. The Thames and Hudson Manual of Dyes and Fabrics. (London: Thames and Hudson LTD. 1978)

John Peter Wild. Textiles in Archaeology, (Aylesbury, Bucks, UK: Shire Publications, LTD. 1988)

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