Direct Dyes
Direct dyes are another class of dyes, one of the two types of dyes that are mixed in ‘all purpose’ dyes such as Rit. (The other type in the mixture is an acid dye, which will not stay in any cellulose fiber for long.) The colours of direct dyes are duller than those provided by fiber reactive dyes, and the washfastness is poor – expect anything dyed with them to ‘bleed’ forever. The one advantage is that direct dyes may be more lightfast, that is, resistant to fading in the light, than fiber reactive dyes. The “direct dye” classification in the Colour Index system refers to various planar, highly conjugated molecular structures that also contain one or more anionic sulfonate group. It is because of these sulfonate groups that the molecules are soluble in water. Though most direct dyes still can be obtained in powder form, it is increasingly popular to receive them as liquid concentrates. The advantage of concentrates is that they are easy to handle and meter. The disadvantage is that the surfactants and co-solvents needed to keep the dye concentrates stable may interfere with retention and sizing in the case of very deeply coloured grades.
Direct dyes are used on cellulose fibers such as cotton, rayon, and linen. They lack the permanence of the cold water fiber reactive dyes which most serious dyers prefer for use on cellulose fibers, but in some cases they have advantages that make their use worthwhile. For example, while many of the direct dyes are not very lightfast, there are some dyes in the class that may be more lightfast than similar shades of fiber reactive dyes. All direct dyes perform rather poorly with respect to washfastness. Without an appropriate after-treatment, direct dyes bleed a little with every washing, losing their brightness and endangering other clothes washed in the same load. However, there are special after-treatments which may be used to solve this problem. (Vinegar is not among them! In spite of claims you may see to the contrary, you cannot use vinegar to set any dye on cotton or other cellulose materials.) A product called Retayne, which is an ionic bulking agent which essentially “glues” the dye into the fiber, works very well to make fabric dyed with direct dyes washable without bleeding of the dye.
The name ‘direct dye’ alludes to the fact that these dyes do not require any form of ‘fixing’. They are almost always azo dyes, with some similarities to acid dyes. They also have sulphonate functionality, but in this case, it is only to improve solubility, as the negative charges on dye and fibre will repel each other. Their flat shape and their length enable them to lie along-side cellulose fibres and maximize the Van-der-Waals, dipole and hydrogen bonds. Below is a diagram of a typical direct dye. Note that the sulphonate groups are spread evenly along the molecule on the opposite side to the hydrogen bonding -OH groups, to minimize any repulsive effects.
These are mixed for black colour to dye silk yarn
Silk is an animal fiber, and therefore, like all animal fibers, is made of protein.
Proteins are made out of different combinations of the twenty essential amino acids. They are more complex than cellulose, which is made out of repeating units of a sugar, glucose, and thus there are more ways in which different dye chemicals can attach to them. There are, therefore, many more different substances which can be used to dye protein fibers.
Silk is less sensitive to high pH than animal hair fibers are. This makes it the most versatile of all fibers for dyeing. It can actually be dyed quite well with the same soda ash recipe used to dye cellulose fibers with fiber reactive dyes. Silk can also be dyed with the acid dyes that are used for wool, or with the inexpensive but poorly washfast direct dyes that are often used on cotton, and has traditionally been dyed with indigo, a member of the class of vat dyes. In fact, you can dye silk with just about any kind of dye, except for disperse dyes, which are designed solely for dyeing synthetic fibers.
Choosing your silk dye
Since silk can be dyed with almost any sort of dye, you need to decide which properties are most valuable for you in your current project. Are you most concerned that the dye be completely non-toxic for small children, or that it be particularly easy to apply, or that the dyeing process not alter the texture or luster of your silk even a little?
Non-toxic. Most of the dyes mentioned on this web site are not significantly toxic, but they are not safe to eat, either. If you want to use a dye that’s safe to use your good (non-aluminum) cooking pots for, and still be able to use your dye-pots for food, then you should use food coloring. Food coloring is not the brightest, most predictable, wash-resistant, or fade-resistant of dyes. However, it is safe to use in your good cooking pots, and it is safe to use with small children, children who are too young to follow standard safety practices. If you’d like to use food coloring to dye silk, see the page Using Food Coloring as a Textile Dye for Protein Fibers.
Many people imagine that natural dyes are the safest type of dyes to use, but in fact natural dyes can bring their own hazards; natural dyes are usually less safe to handle than food coloring, as textile dyes, and most are less suitable for dyeing baby items than fiber reactive dyes.
No heating and no steaming. If your primary concern is to avoid investing right now in a dyepot, or to avoid bothering with simmering or steaming your dyes, then you should use a cool-water fiber reactive dye, such as Procion MX type dye. You can dye any washable silk with the same soda ash recipe we use for dyeing cotton with Procion MX dyes. It’s perfect for tie dyeing, batik, low water immersion dyeing, dye painting, or any other form of direct dye application. It can also be used to dye silk in the washing machine. The only drawback is that the soda ash will make the silk a little less shiny and a little softer; sometimes this is desirable, but if your number one priority is to maintain the stiff texture and shiny luster of your silk, then you should use some sort of acid dyes, instead, although they will require some heating.
Alternatively, there is a way to fix Jacquard Green Label Silk colors at room temperature without the use of a high pH; these dyes are mixed to have an acidic (low) pH, although they are Remazol fiber reactive dyes.
A third alternative, if you do not want to steam your silk, is to use fabric paints or even fabric markers, instead of true dyes.
Wash-proofness. The best dyes for staying bright even after washing are the cold-water fiber reactive dyes, such as Procion MX, when used with soda ash, and the Lanaset dyes when used as directed. The metal complex dyes, such as KraftKolour’s Premetallised Acid Dyes, are also very good. (In fact, some of the Lanaset dyes are metal complex dyes.) If you want an extremely long-lasting, wash-proof dye that does not make your silk a little softer, use Lanaset or metal complex dyes, both of which must be used either in a boiling dyebath or with steam-setting afterwards.
Good for silk painting. Any of the dyes mentioned above, with the exception of the food colorings, are good for silk painting, but you will have to mix your own colors. Procion MX dyes should be used within a week of mixing, but the other dyes stay good in water for up to a year, or in some cases longer.
