Küpe is a living thing. It is different everyday depending on weather, what was colored the day before, what you have add… it colors differently. We check pH and temperature each day and take a note. Then dip a test piece of fabric to check how good it dyes on the day.
You should also check when you first dip the white fabric. It should look a bit brown. Let it dip for 10 min and pull it up in the air. The oxidation starts. When it is coloring good, It looks yellow green first, then starts to turn to blue. as the water starts to drip on the bottom, the bottom edge stays yellow green, while the rest of the fabric continue turns to blue.
The color of the change, speed of the change and the end point color informs you if it is good reduced in the Küpe (if not, it needs more eisen sulfate, which you would add in the evening), if it is too cold (then the color will be very light) or it needs more indigo pigments ( so I was told…) A lot of this readings of Küpe come from the experience… and someone like Janina who is working with it for many years really have a “gut-feeling” of what Küpe needs.
Oneday, we added Kalk(400g/Küpe) in the Küpe to increase the pH so the reduction of the Indigo happens more. The next day, the test stripe comes out in brown-red color (the photo does not show so well, but it was really surprisingly red) instead of yellow green as the other days.
After waiting, it did turn into blue color. so I proceed with dying. But the whole day I had the feeling that the blue today is wrong. It had more of the red-tint rather than the green-blue of indigo fabrics.
Küpe is a living thing and it is interesting that it is not the same each day. Everyday is a gamble. Until one finishes all the process and wash it, hang it and see the dried fabric, you never know what you are getting.
Janina from Zeugfärberei has been working with this Küpe for long time and she has a “gut feeling” of what needs to be added. I often ask her at the end of the day, like a villager asking the oracle “what do you think we should add today?”
At the end of this day, the oracle Janina suggested to add a bit of (200g/Küpe) eisensulfate. The result will not be known until the next day as the Küpe needs sometime to “digest” what has been added. Cross fingers!