You can find some colorfastness tests here:
Natural colours vs. synthetic colours: Using synthetic dyes is cost-effective and may allow to your textile a lower price…, but part of good business practice is finding solutions for your needs that are sustainable and that has the least negative impact on the environment.
Natural dyes vs. synthetic dyes: natural dyes are perceived as harmless and safe for the environment. We have solved the common problems of the classical way of natural dyeing: all the raw materials are traceable, non toxic, environmentlly safe and social fair labor.
What touches the skin?: Synthetic dyes cover the fibre just as it does a polymer paint, coating the base material with a uniform layer. By contrast, the molecules in natural dyes combine with the fibres, not covering it, but bonding to it. In the case of synthetic dyes, what touches the skin is not the fibre, but the synthetic dye, generating allergenic reactions. With the natural dyes what touches the skin is the natural fibre and/or the natural pigment.
Taking the right choice
1) Fading: Natural dyes are aesthetically superior to synthetic dyes: they evolve and mature well and develop a characteristic patina when exposed to sunlight and normal use, creating a patina that provides a pleasant appearance, with slightly irregular tones. Natural dyes fade softly and unevenly, leaving lighter shades that are just as beautiful, if not more, than the original color.
2) Harmony: Natural dyes have a range of colors that are much more compatible and harmonious than chemical dyes. The natural dyes are more aesthetic, because they are not unique hues, and so the natural colours convey harmony, not only call attention by its brightness. The natural and harmonious combination makes a high value for the consumer. Natural colours always offer shades and ranges of hues impossible to achieve with artificial colourings. The colors obtained from natural sources tend to be softer and subtle, richer in a chromatic range. Synthetic dyes often produce striking colors. Natural red, for example, will include blue and yellow, whereas a chemical red will only contain red pigment. The “impurities” of natural dyes, which may comprise from 5-25% of the dye, consist of other hues that are similar to the main one, and it is these mixtures that make natural dyes so beautiful and create their harmony with neighboring natural colours. Each plant provides an amazing diversity of shades. These colors and shades are subtle and tend to harmonize with one another.
3) Shade: Like wine, which contains many phenolic compounds that give it the complexity of aroma and color, natural dyes also contain a multiplicity of polysaccharides which are responsibles of the complexity of color, of the relief and of the maturation of color and aging and wear of the fabric. Natural dyes make different shades all along their life. When these natural dyes are exposed to the sun light and to wear, they leave lighter tones, which makes them to look beautiful in different way than their original colors. Like Denim does. The slight color differences of a dyed lot to another is also a positive aspect to consider.
4) Intensity: Natural color is inherently more muted than chemical color, which looks very stark. Colors obtained from natural sources tend to be earthy and subtle. So, if chemical colors are used, while the desired effect is a “natural” look, it will be necessary to mix a variety of colors in imitation of nature and also artificially create some wear. Natural dyes are good for washing and sunlight. In our case we have managed to reach the colors fastness factor to the same level as the chemical dyes. But the use&abuse of a naturally dyed clothe makes the garment even more attractive.
5) Lasting: Color created from natural elements lasts much longer than chemical dyes. The wear effect in a natural dyed fabric gives to the apparel a new life and color while it becomes aged. The synthetic dyes fade all the color at the same time, so the effect is not of aging, but of a lost of beauty. Moreover, synthetic dyes, when at all degraded, are full of byproducts that are directly or indirectly proven to be health hazards; such hazardous compounds are not present in the Natural dye degraded byproducts. Natural dyes completely degrade under natural conditions.
6) Price: Natural dye materials normally are scarce and expensive. For example, cochineal is more costly per ounce than gold. Synthetic dyes are readily available at low cost, resulting in a less costly rug to produce. Our dyeing procedure is comparable in cost to the synthetic dyes.
7) Fastness of color: “classical” natural dyes do not endure washing or sunlight. Our natural dyes fulfills the standard rules of the global textile industry, reaching a washing fastness of 4-5 (maximum is 5) and a sunlight fastness of 6 (maximum is 7).
Beneffits of the natural dyes
Benefits for the environment: Natural dyes have minimum environmental impact, since they come from natural sources; they are not harmful to the environment, they are biodegradable. The natural dyes are obtained from renewable sources that can be exploited without the consequent harm to the environment. Natural dyes are biodegradable.
Consumer benefits: the use of natural dye avoids allergies related to chemical products. Due to the absence of toxic waste, naturally dyed fabrics are more pleasant and beneficial for the skin. Clothing is one of the primary causes of dermatitis and allergic reactions (due to resins and formaldehyde).
Producer benefits: it is not toxic, preserving the health of the workers (inhalation and contact), unlike the commonly used chemical dyes. There are no dermatological reactions even during their preparation.