Report on Lightfast Testing
Dyeing With Food Coloring

Vikki Clayton 2005

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Preliminary results for the lightfast testing.

To recap, this is a test of cross stitch fabric, hand dyed, under a number of conditions. It was then subject to intense light under ASTM conditions for lightfast testing.

The first blue wool standard strip has faded considerably, exposed to about 0.4 megalux hours. To set this in perspective, average indirect indoor lighting (at about 120 to 180 lux) for an average 12 hours a day equals from 0.53 to 0.79 megalux hours each year. THIS IS NOT EXPOSURE TO DIRECT SUNLIGHT. This is merely exposure to the average indirect lighting that a normal household experiences. This means that these fabric samples have been exposed to less than the average indirect lighting a normal household experiences in a year!!!

First the powdered drink mix dyed fabrics. This common at-home method is often used for cross stitch fabrics though it's a method that's recommended for wools and silks only. You can see why from the pictures. It's not possible to set powdered drink mixes, or food coloring, on cellulose. Less than a year of normal household light exposure has severely destroyed the colors.

6. scoured fabric dunked in a solution of powdered drink mix
7. non-scoured fabric dunked in a solution of powdered drink mix

Scouring the fabric first actually exposed it to more light, and increased the color destruction process.

This method of cross stitch fabric dyeing is something that might be fun to do at home, for a short lived project such as birthday card or for an ornament or other project that might be displayed only a few hours a year, or under very dim lighting conditions. Certainly this wouldn't be an appropriate method to dye a piece that you'd want to display continually or to be an heirloom treasure.

What does all this mean?

The procedure to dye cellulose (cotton, linen, rayon) is time consuming and takes several steps to achieve a good bond between the dye molecule and the cellulose molecule. Based on these test results it would seem safe to conclude that using methods to dye that are not forming these bonds are more susceptible to light damage.

Lightfastness is tested on a 1 - 8 scale. Most of the reactive dyes (those that form a bond with the cellulose) fall in the 4 - 6 lightfastness range ( 4 - 5 is equivalent to about 15 -50 years and 6 for 50 - 100 years worth of light exposure without change in pigment with proper mounting and display). As an aside it tends to be the reds in the 4 and 5 range which is why you often see the red burned out of a color long before the other colors.

Acrylic paints are also tested for lightfastness and often have the lightfast rating on the paint packaging. Acrylic paint doesn't ever dry completely so you must display it under glass to prevent dust molecules from embedding in the paint. Still it seems to be a viable fiber or fabric coloring method.

While all dyes fade there are several steps that you can take to prevent this.

All dyes fade. But the best way to ensure that your fibers and fabrics will not be subject to an early demise from fading dyes is to utilize a two-pronged approach. First, if you are using hand dyed or variegated cellulose request information from the dyer as to the methods used to dye the cellulose. A method that includes using reactive or fiber dyes with a mordant of soda ash or an acrylic paint with a good lightfastness rating of at least 4 seems to be the best protection against premature fading. Of course factory dyeing does not use these types of dyes. You should be able to tell a hand dyed variegated from a factory dyed variegated - the factory dyed will have exact even repeats.

The second prong is good storage methods. UV and visible light both cause fading, so framing with UV glass will only protect to some extent. Lessening exposure to any source of light is best. It's noted that oxygen may be needed to drive the fading reaction, but it doesn't seem feasible to store or exhibit articles at home in an inert gas!

There is an excellent article on this site under Articles, Silk Facts and Fantasies, Storing Silks that outlines various methods for archival storage. While it focuses on silk, these methods are also apt for cellulose.

Editor's Note :  To access the results of testing with dyes other than the food dyes see the complete series of articles.

ASTM International, was originally known as the American Society for Testing and Materials

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