Name: Elizabeth

Message: your website is wonderful -
my question is -
i have dyed some very small pieces of silk chiffon with food coloring. they will eventually end up as part of a mixed media piece, framed under glass. -- all the dyed pieces of silk are dry now so - regarding their lightfastness: is it too late to steam them? will it help at all? and if so, must they be wrapped in plastic for a stovetop steamer, or can they merely be placed on it? will ironing help at all? or hurt? or do nothing?
i have combed over your site, and parts of this question are dealt with but not, that i can find, all put together as such & pertinent to food color on silk.  please pardon any redundancy if it is the case.

It's not too late to steam your silk. In fact, the most usual way to steam dyed silk is to let it dry, and then steam at a convenient time. 

Do not wrap dry silk in plastic wrap for steaming: plastic wrap is suitable only for fully wet fabric or yarn. Moisture in some form is required for any dye to bond to the natural fiber. Instead, wrap your dry silk in layers of unprinted newsprint paper. The silk is protected from other parts of the silk by layers of paper. For pieces of silk that are too large to fit in the steamer pot as it is, roll the paper up with the silk inside, then coil the paper roll, to make a shape that will fit in your steamer. Steam for twenty to thirty minutes, unless instructed otherwise.

Unfortunately, while steaming will help with washfastness, I am not sure how much good it will do for the lightfastness of the pieces. It is a good idea to do the steaming, since properly fixed dye is in general more light-resisatnat than dye that has not been fixed to the fiber. Food coloring is not particularly noted for being resistant to fading from light. I am sure that ironing will make no appreciable difference in the lightfastness of any dye, since dry heat does not encourage dye to bond with the fiber; dry heat is used only for acrylic-based fabric paints. Framing under glass will help a little, especially if the glass is a little tinted, so that it reduces the amount of visible light that reaches the fabric. Ultraviolet protection sprays will not help at all, from my observations.

The most light-resistant of dyes are the vat dyes, including the light-developed Inkodyes sold by Dharma Trading Company. Pigments are in many cases more lightfast than dyes, so fabric paint is in some cases a better choice than fabric dye, when items will be exposed to light but rarely if ever washed. Some acid dyes are acceptably lightfast, while others are not. Food dyes are a type of acid dye. I'm sure you have already looked at my page on Lightfastness of Different Types of Dyes, which, when you wrote, did not include ratings for food colorings. (I will be adding them.) Lightfastness ratings for acid dyes range from 1 (very poor indeed) to 7 (quite lightfast), on a scale of 1 to 8. Published numbers for the lightfastness of food colors range from 3, which is poor, to 6, which is acceptable. It is unknown how these values will shift when the dyes are applied to silk. Some dyes, such as Procion blue MX-7RX, are more lightfast when they have been applied to silk.

All Colour Supplies Pty Ltd of Australia claims the following lightfastness numbers for food colorings:
Indigo Carmine

name	CI #	CI name	FD & C	E. Code	Class	Light Stability
Tartrazine	19140	CI food yellow 4	FD & C yellow 5	E102	Monoazo	6
Sunset Yellow	15985	CI food yellow 3	FD & C yellow 6	E110	Monoazo	4
Erythrosine	45430	CI food red 14	FD & C red No.3	E127	Xanthene	3
Allura Red	16035	CI food red 17	FD & C Red No.40	E129	Monoazo	5
Brilliant Blue	42090	CI food blue 2	FD & C Blue No.1	E133	Triaryl- methane	5
73015	CI food blue 1	FD & C Blue No.2	E132	Indigoid	3

Note that lightfastness may be significantly altered for dyes that have been attached to textile fibers, and that the lightfastness may be very different on oen fiber than another; however, we have no information about how the lightfastness of food coloring smay change once they have been binded to silk or any other textile fiber.

As you can see, under the conditions used for testing by the All Colour Supplies company, Tartrazine (FD&C yellow 5) is a better choice, for light-fastness, than Sunset Yellow (FD&C yellow 6); Allura Red (FD&C red 40) is a better choice than Erythrosine ((FD&C red 3); and Brilliant Blue (FD&C blue 2) is a better choice than Indigo Carmine (FD&C blue 1). A lightfastness of 5, on a scale of 1 to 8, is ranked as having "fair" lightfastness, and according to the ASTM lightfastness standards (see the chart on Bruce McAvoy's site) "will remain unchanged for 15 to 50 years with proper mounting and display." ("May be satisfactory when used full strength or with extra protection from exposure to light.") Tartrazine's lightfastness rating of 6 "will remain unchanged for 50 to 100 years of light exposure with proper mounting and display."

As it happens, each of the better colors of these three pairs are the ones more commonly found in food colorings, so you may have used the more light-fast dyes without knowing about their lightfastness. Indigo Carmine is highly susceptible to damage from heat, so it probably should not be steamed, if you used it. I have found it more difficult to find Indigo Carmine, however, so you probably did not use it.

Among natural food colorings, lightfastness is very poor, poorer than that for synthetic food colorings. Cochineal is used in the artists' pigment carmine; Bruce MacEvoy rates it as completely unacceptable for painting due to its poor lightfastness. Turmeric, a spice that is used as a natural yellow food coloring, is noted for poor lightfastness, as well, as are most natural yellow dyes.

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