Indigo Dyeing (through the lens of high school chemistry )

A couple of years ago, I wanted to know more about what was happening with indigo "dyeing" (it's really using a pigment as it is not water soluble). I don't really buy the idea that it's "magic";  it is chemistry

(Here's a sample with shibori stitching technique done at Daufuskie Island a couple of years ago):

So, I did some research and thanks mostly to wikipedia came up with the following 

Indigo pigment is derived from indican, a compound found in leaves of various plants including Indigofera tinctoria, Indigofera suffruticosa, persicaria tinctoria (Japanese indigo) and isatis tinctoria (woad). The leaves of the indigo plant contain very small amounts of indican, 0.2 to 0.8 %.  

Indican is a colorless, water-soluble derivative of the amino acid tryptophan. Indican readily breaks down in water (“hydrolyzes”) to release β-D-glucose and indoxyl.

 

Plant leaves are soaked and fermented to produce the blue residue containing indigotin/indican. For shipping or forms of storage, the precipitate from this process is mixed with a strong base such as lye, pressed into cakes, dried and powdered.

 

Indigo is a challenging because it is not soluble in water (it cannot dissolve in water; this is why it is not a dye). To be dissolved, it must undergo a chemical change or “reduction” in which oxygen is removed from the water containing indigo powder. Reduction converts indigo into "white indigo" (leuco-indigo). When a submerged fabric is dipped in removed from the bath, the white indigo quickly combines with oxygen in the air (oxidizes, which is the opposite of reduction) and indoxyl reverts to the insoluble, intensely colored indigo left on the fabric (or paper).  Thus, what is dipped in the bath must be done so carefully in order to not introduce oxygen from the air into the bath.

And...there you go.

 

Saxon Blue Dye

I was rummaging through my collection of dyes in the garage and found some Saxon Blue in liquid form, which I've had for a few years. I went to the Botanical Colors website for some helpful tips. 

This is a dye which the Germans developed from indigo in the 1700's. Someone acidified it...as we know acid is a common feature of synthetic dyes.  (The company that is now BASF later developed a synthetic indigo, so they may have known that they were onto something with the acid thing...)

It is not a vat dye like indigo, so I pretreated my handspun yarn samples with a simmer in an aluminum acetate pot (with a tsp of AA) for an hour. I'm no longer using kitchen alum for mordanting but I don't know whether this makes a difference...another experiment to do...

Now, I don't like to measure so I didn't! But I have discovered using pH strips that my tap water is pH neutral.

I emptied the dye, about an ounce of liquid into warm water and dropped in my six small skeins

It simmered for an hour, but the yarns were still pale blue. BC suggested adding vinegar so into the pot went 1/2 c of distilled vinegar. In stand success! Here are the dried samples, some sheep's wool, some mohair. I've noticed in my dyeing practice that sheep's wool tends to take up more color.

Now, there was still some dye in the pot, so I decided to add two more small skeins and some bundles of osage orange shavings.  

 After an hour, the pot again required 1/2 cup of distilled vinegar.  Voilà again...a lovely grassy green!  The fabric holding the osage orange was also mordanted so I have some dyed fabric samples to give away too!