How to Best Pair Leather Dyes with Compatibility In Mind
There are many things to take into account when choosing a dye class to work with for leather treatment. Compatibility of the dyes considers the working properties and performance of each dye. These characteristics will help you determine which dye best fits your production. After deciding what dye class is suitable, then you can get to the fun part of creating the color. It’s important to be aware of the capabilities of all the dye ranges used for leather. We’ll review the basics of each class and then the common tanning processes.
Dye Classes for Leather
There are several classes of dyes used for coloring leather, the most popular are the following groups:
- Acid dyes
- Direct dyes
- Basic dyes
- Sulphur dyes
The name “acid” derives from the dyeing process. Because we add the colorant at the same time as organic and inorganic acid, we call the dye “acid.” In an acidified water solution, the dye acts as an acid and combines with the basic groups of the skin.
To obtain level dyeings, once you add the color it should run about 20 minutes or more depending on how deep of a dye penetration you want. More time will help in the leveling of color on the substrate. Acid dyes produce clearer and brilliant shades. They’re also great for creating “fancy” shades — pastels, vivid oranges, reds, greens, or blues. The acid dyes are indispensable.
These dyes are compatible with other dyes, except basic dyes. Since they’re active on opposite pH spectrums, it makes sense they don’t perform well together.
Direct dyes are a class of synthetic dyes used for coloring leather. Direct colors are more or less sensitive to acids. If the leather is too acid when applying the dye, there will be uneven depositing of color on the surface. Raising the pH above 5 will help the levelness of direct dyes on leather.
Most often, we use these dyes because they give a strong, full color. They dye level and have good coloring value. One setback is that direct dyes are not as bright as acid dyes. They vary in lightfastness from poor to outstanding. Most have limited wet fastness in medium to full shades unless aftertreated.
Basic dyes are ionic dyes in which the colored part of the molecule is cationic, or with a positive charge. As a class, they have high color value and are among the brightest dyes available. Basic colors give full and level shades if the right selection is made. These basic colorants are not as fast to light as most dyes belonging to other classes.
Solubilized sulfur dyes are used extensively to dye leather because of their ability to provide deeper penetration, high wash fastness, and high lightfastness.
Making the Dye Stick to the Leather
Applying dyes to leather is an involved process. It includes the competition of many reactive materials with each other to fix onto the hide fiber. Here we look at two common leather tanning processes and how the dyes come into play.
Neutralized leather is needed in dyeing chrome tanned leather. You can do this by raising the pH level of the hide. Once introduced, the dye penetrates into the skin. Before or in combination with the dye, we add a naphthalene or anionic syntan. This will cause competition between the syntan and colorant for positions on chrome tanned leather. This competition actually causes better shade leveling and greater dye penetration.
In retanning, we apply colorants with vegetable tanning materials to give a base color to the leather. Once the dyestuff penetrates, we lower pH by adding a weak acid. Now, the reaction between the leather and the colorant is complete. At this point the fixation of the dye may not be permanent. In the later fatliquoring step, the strong sulfonic acid of the oils could result in displacement of dye from the leather. This is something to be mindful of.
The amount of dye used varies depending upon the type of leather in production and whether using a penetrating or surface type dye. In the manufacturing of side leather, usually only a light to medium color (less than 1 – 3%) is necessary. The dye applies on the surface to give a base color over which the finish will rest. With suede leathers, we need deep dye penetration. To get the desired shades, as much as 15% of dye may be necessary.
It’s important to be aware of the compatibility of the dye classes to select the best dye for use. In selecting a dye for leather and creating dye formulation, it is not enough to merely combine two or more dyes to create a specific color. Shade strength, procedures, and conditions are all things to take into account. Consider the connection between dye and leather when picking a dye to use in your processing.
Need help picking the dye that’s best for your process? Our Leather technicians from our leather lab can help with your next dye match.
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