ozone & indigo

Recently, in the workshop at the Japanese American National Museum one of the participants brought some fabric that she had dyed in another workshop somewhere.  It had faded radically and even more so along the folds and creases.  She wanted to know what had happened.
This is something that also came up a couple of times in the online indigo workshop and was struggled with over there.  Occasionally, I have seen it in my own indigo dyed pieces and strive to do those things which I find help to alleviate the problem.
As far as I have been able to understand, and the experiences I have had with this type of fading have led me to the following understandings.  Please feel free to jump in here and correct , inform and add to our knowledge on this for other folks as well.
The issue:
-fading of the fabric along exposed areas and folds where the cloth is exposed to air and or humidity. I have even seen fade lines on indigo cloth that I have hung (flat) to dry outside overnight that had a bit of a sway in the hung cloth. It seemed that in this case the overnight humidity was the over-riding factor.

three shades from the fermentation vat ready to assemble into the cloth packs for the shop

What is happening?
– ozone in the atmosphere is reacting to the cloth and any chemicals left in the fabric and additionally with UV light to produce an oxidizing effect. Smog and humidity also figure into the mix even in cloth that is well washed out.

At first, I thought that only fabrics dyed in a chemical vat or a pre-reduced indigo vat were susceptible to this.  Not true.  They may be MORE prone to it but fermentation vat dyed indigo is also affected.

What to do to minimize this?
– wash out your fabrics well before dyeing to remove any chemical treatments.
-build up your depth of shade over many dips in the vat. Have a light vat and a dark vat to produce various shades of blue through repeated dips and really work the dye into the cloth.
-rinse your indigo dyed cloth well between dips into the vat and then finally wash them well with a good rinse in the end.  You may have seen photos of Japanese dyers planting their indigo dyed cloths along a river or stream to let the water run through- this would definitely do it!  Getting out any chemicals that can react to the ozone is beneficial.
-once dried and ready for storage until use, you can keep your indigo cloth in a drawer or wrapped in a towel to keep the edges from fading.

Finished pieces (such as a quilt on a bed, a pillow, a wall hanging) will fade more evenly and possibly without notice as they are more evenly exposed to the atmosphere. All indigo will fade with use (think denim).  Well dyed dark shades built up by many dips seem less susceptible.   This is one reason I prefer the fermentation vat over the pre-reduced or chemical vat-more work but a more satisfying process and result. Also, be aware that different fabrics will fade differently. Think about the weave and the fiber.

There are even products out now for commercial dye houses that speed indigo fading (ozone finishing!) with the use of ozone related treatments said to be less labor and water intensive. Consulting companies work with manufacturers to troubleshoot their process and diminish the fading (or even speed it up!).

What if it’s not a problem at all?  It’s a matter of perspective.

Yesterday’s moon- on an open weave linen