Sunday, October 3, 2010

Resist vs Discharge

There are 2 ways to 'print' indigo. The earliest approach is to print a resist on the undyed cloth. The resist can be mechanical--flour, starch, clay, resin, or wax--or chemical--salts of copper, alum or zinc. The length of fabric is then processed in an indigo dye bath. The pattern printed resists the indigo dye. A rinse of warm weak sulfuric acid removes the wax or zinc salts and you have an off white design on an indigo ground. Wonderful! 

Early in the 19th century a second approach was developed--the discharge method. The fabric is first dyed indigo blue and then a discharge paste is printed on that fabric. The oxalic acid 'bleaches' out the pattern design. The look on the printed indigos is similar. I have had people tell me they could tell the difference. Alas, I was not able until recently. In March I purchased some quilt blocks from a Senior Citizen's Center in eastern Ohio. There was one group of 8-pointed stars dated c. 1825 which had several indigo prints.  The back of one was different from the others. I think you can see how deep blue the back of this indigo piece is. 

There were pieces in other blocks whose backs look like this. You can see a 'shadow' of the design on the back. I think now if I can see the back, I might be able to detect Resist vs Discharge.
I thought you would want the see the fronts of these two blocks!


2 comments:

  1. So which is which?

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  2. I think the deep blue back version is the resist. The paste resisted the dye on the front but some dye reacted with the back of the fabric where the resist did not penetrate. The discharge paste 'bleached' out the indigo dye all the way through from the top to the bottom. I have some lovely,gaudy 'illuminations' (always by discharge) in another block from this group and will show those on the next post.

    Also the 'plaid' piece is a much deeper, more purply shade of blue and if you do a close up, you can see the design is 'rough'. So I think this may be an older fabric which may have been produced by the earlier method.

    I am doing a presentation on Indigo at AQSG next week in Minneapolis. I am taking these blocks along for comments!

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