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Jim Liles, in his book "The Art and Craft of Natural Dyeing", recommends aluminum acetate for cotton for better color
results. I tried it and now use it routinely not only for cotton but for bast fibers, rayon and Tencel. It makes a significant
difference in the color take-up and gives improved lightfast ratings compared to cotton mordanted with potassium
aluminum sulfate. Aluminum acetate is a salt obtained by reacting aluminum hydroxide and acetic acid. It is more expensive
than the technical grade of alum and is not as readily available from every chemical supply source. One of the interesting
uses of aluminum acetate is as a petroleum drill bit lubricator. Otherwise it can be used interchangeably with alum for most
uses. Since it is made with acetic acid, an organic acid, more processing is required to manufacture it. Both because there
is less demand and the aluminum acetate takes a lot of refining, it remains more expensive than common alum. I
recommend that you always wear a dust mask when measuring aluminum acetate, as the acetic acid can be irritating to
your nose and lungs.
Alum Percentages for Dyeing
Finally, you ask, how much alum do I use? And how do I mordant properly? There are so many right ways. First of all,
many recipes call for using alum at 25% on the weight of the goods (WOG). However, this figure can be decreased
significantly if mordanting wool. I use between 8-15% WOG depending on the depth of color I want and whether I am
mordanting wool or mohair. If mordanting silk for the red dyes (cochineal, lac and madder), I increase the alum percentage
to 20% WOG. Tagua nut buttons need just 4% WOG. And, even using these decreased amounts, only approximately 25%
of the alum is used. Therefore, the alum bath can be refreshed and reused again. Because of its water purifying
characteristics, I do not recommend reusing the alum bath more than two times. If I am mordanting cotton or bast fibers
with aluminum acetate, I typically use 5% WOG.
The alum mordanting bath can be heated or not. The temperature of the mordant bath may range from 180-195°F for one
hour for wool, mohair and other animal fibers to 100°F for one hour for cellulose fibers. Silk may be heated at 175°F for
one hour or left at room temperature for three days to one week. Once fiber is mordanted with alum, curing for a number of
days before dyeing will increase the amount of alum that attaches to the fiber and, therefore, result in a darker color when
dyed. This is a technique that a craft dyer can take advantage of that a commercial dye house cannot. Another mordanting
tip is to leave the fiber or cloth damp with alum after removing it from the mordant bath. You will get deeper colors if the
fiber is not dried before dyeing. However, short drying periods do not affect the natural dye intensity when painting on silk
cloth following the direct application of alum.
For more information, see Earthues Natural Dye Instruction Book for detailed mordanting instructions.
Earthues, A Natural Color
5129 Ballard Avenue NW
Seattle, WA 98107
Telephone - 206-789-1065