Alum – Aluminum Potassium Sulfate

Cellulose fibers are mordanted with aluminum acetate, and wool/protein fibers and silk are mordanted with alum, either Potassium Aluminum Sulfate or Aluminum Sulfate.  From what I’ve read, I understand the main reason for recommending Potassium Aluminum Sulfate over Aluminum Sulfate, is really about purity, as some sources of Aluminum Sulfate could have iron or some other impurity that could affect the clarity or color.  There may be other reasons, but I’m just giving you the quick and easy, because much can be explored and delved into further on the subject of natural dyeing.  I’ve read that you can also try aluminum acetate for a brightened effect on wool. 

The recommended amount of aluminum sulfate to mordant wool is between 10-15% of the weight of fiber, but I’ve read that for improved lightfastness with Logwood, you can use 22% alum.  More mordant can be used, but generally, 10-15% is sufficient.

An easy thing to remember, for me to mordant at 10-15%, when mordanting wool with alum, is to just use 1 scant Tablespoon for 100 grams (3.5oz skeins) or 1 good Tablespoon for 4oz skeins of fiber.  You can go up to 20% of the fiber weight by using 1 Tablespoon + 1 teaspoon per 100 grams (3.5oz) of fiber. More mordant results in deeper shades with many of the colors, especially the red dyes, or in logwood’s case, increased lightfastness.

Cream of tartar should be 6% of the weight of fiber, or 1 1/4 teaspoons for 100 grams (3.5oz) of fiber. You can use aluminum sulfate and cream of tartar together, the cream of tartar brightens many colors and helps keep wool fibers soft.

You can simmer the wool and mordant together in a pot for 1 hour and use it immediately with a natural dye, or dry and store in a clean place so that it is ready to use in the future.  No future further mordanting is needed, as the mordant is already bonded to the fiber.  I have read that best results may be obtained from mordanted fiber that was dried and let sit before use, but this is not necessary for good results. 

If you want to mordant a lot of wool, it is easy to cool mordant in a 5 gallon bucket, making sure your fiber has a lot of room to move around and that every part of it can be accessed by the mordant.  You can reuse this mordant solution, and just add 50% of the alum and cream of tartar per amount of fiber that you did the first time.  I put a lid on my bucket and it stays clean and ready to use.  It is said that it may be best to use the fiber or take it out to dry and store for future use, after 1 week.  I don’t know if leaving the fiber in the mordant solution longer is a problem for the fibers, and that wasn’t explained, so I’m just sharing what I’ve read. 

This information is just to give you very basic and easy instructions on how to mordant with alum.  It is meant to be a jumping-off point by which you can delve into the joy of discovering for yourself what colors are contained in the nature around us.  Natural dyeing gives me that childish joy of discovery and concocting, and I hope it will do the same for you.