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Ever since the discovery of the aniline dye Mauve by William Perkins in 1856, the first synthetic dye derived from coal tar to be manufactured on a large scale, there has been a debate about whether synthetic dyes are better then natural (plant/insect derived) dyes. We get calls all the time about whether natural dyes are more organic, or better for the environment, or safer to use, than synthetic dyes. So follows is a brief (really, believe it, we have cut this way down!) discussion of the pros and cons of dyeing with Natural Dyes vs. the most popular types (for home use) of Synthetic Dyes.
Natural 1
In the early days of synthetic dyes the debate was merely one of cost and performance as the industrial age had yet to see the rise of concern about pollution and worker safety issues. As it became apparent that certain types of cancers were linked to exposure to early aniline type dyes, their use and manufacture was phased out. Now we know about the health concerns of dyes and also about the environmental impact that results from their manufacture and use.
Natural 2
As more people have become interested in organic and other more natural options for clothing, along with heightened awareness of chemical sensitivities, there has been a growing interest in natural dyes. The feeling by some is that because they are extracted from natural sources they must be more environmentally friendly and healthier for the consumer. However, natural dyes are often neither safer nor more ecologically sound than synthetic dyes. Some folks who have a business dyeing organic clothing or yarns have actually switched from Natural Dyes to Synthetic dyes (Fiber Reactive) for reasons discussed below.
Natural 3
There are many downsides to naturals dyes; they are less permanent, more difficult to apply, less wash fast, and most require the use of mordants, which bond to the fiber on one end and the dye molecule on the other, some of which are highly toxic. Some natural dyes such as Logwood, which Hematein is derived from, are themselves significantly poisonous. Rhubarb leaves, which are often used as a mordant, contain Oxalic Acid, which is toxic, but the stalks can be safely made into pie. Color possibilities are more limited with natural dyes, even if one is willing to use the more toxic mordants and modifiers. Some of the metals, such as chromium and tin, are extremely toxic. Even copper and iron mordants can be dangerous if misused, because over time they can build up in the body and cause harmful effects. Alum, Aluminum Sulfate, is the most popular and least toxic of the mordants, however, it is an irritant, and may be harmful if ingested, so it should be used with care. Always wear a dust mask when working with powders. Keep all of these out of the reach of children and pets!
Natural 4
The last problem with natural dyes is the amount of water and heat used. First the fiber must be mordanted in one simmering bath, while the dyestuffs simmer in another to extract the actual dye molecules from the plant or insect material. Once the fiber is mordanted and the extract is ready, then the fiber must be simmered in the dye extract. At the end the fiber must be washed to remove extra dye that didn't fix to the fabric and plant material that was not properly filtered from the extract. While there are ways to mordant while the fiber is in the extract bath, the results tend to be less brilliant and only reduce the water usage by about a third. This process takes a lot of time and energy compared to Fiber Reactive type dyes, which can be used with low water immersion techniques and do not require hot water or simmering for long periods of time.
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