Indigo dye day

Earlier this week fellow OCA student Claire and I spent a day dyeing with indigo. The idea came up when I was researching Aztec culture and design for the Cultural Fusions project. That project is on ice while I transfer courses in OCA, but we weren’t going to cancel the indigo (nor the cochineal – coming soon). I’ll add a link to Claire’s post about the day when it’s up. Claire’s post is here.

indigo_07Both of us have done a little dyeing with indigo before, but always with a vat prepared for a group – never by us. We used synthetic indigo from Batik Oetoro, weighed, measured, mixed, and waited an hour. We were so excited by our first sight of the result – photo to the left. A thin film of dark purple-blue on the top, and underneath a beautiful yellow-green.

indigo_08This is Claire, gently stirring. Oxygen is the enemy in an indigo vat. The indigo will react to it, turn blue … and not be available to dye your goods. Lower damp fabric gently into the vat, leave for a time, lift it out (trying not to drip into the vat – that would introduce oxygen). The fabric comes out yellow green, then before your eyes the indigo blue develops. Very satisfying.

Both of us came prepared with experiments. There are some basics with indigo – the vat must be alkaline, the indigo must be reduced (oxygen removed) – but every resource I checked seemed to have its own “magic” process. How long should the fabric stay in the vat? Longer means deeper blue – but is that two lots of 15 minutes, or 1 dip of 5 minutes followed by repeated 1 minute dips (up to a dozen), or 20 minutes followed by 2 minutes followed by repeated 30 second dips? One source referenced a traditional Japanese process involving multiple dips over days, with rinsing and drying in between (more variables).

I had a complex plan based on a total of 30 minutes in the vat. I would dip 6 swatches for 5 minutes. 5 would go back in for a second 5 minutes. 4 in for a 3rd dip etc. Secondary plans were also based on 30 minutes: a swatch would go in for the full 30. Another would have 2 dips of 15 minutes each. Et cetera.

It didn’t happen. I did the first 5 minutes, then let the swatches oxidize while pottering around with other things. They looked a very dark blue, so we kept using 5 minutes as a standard. I rinsed and ironed dry a swatch and it looked a good, rich colour. I wish now I’d been more disciplined – with calmer eyes that blue isn’t quite so rich and deep.

indigo_04A second experiment was based on weights of fabrics. Three 40 cm squares of cotton were pleated and each was tied between a pair of DVDs acting as a resist (that is, reserving an area that won’t be dyed). The cottons were a gauzy open weave, a voile, and a mid-weight cotton (left to right in the photo). All spent 5 minutes in the vat. The colour is richest and brightest on the voile. I speculate there is less material to hold the dye on the gauze, and not enough time for the dye to penetrate the thicker fabric.

indigo_02Claire brought along a cold wax (emulsified paraffin wax), also from Batik Oetoro, for us to try. I was very excited by the brushmarks I was able to make, and with the easy washout in warm soapy water. My choice of a pink fabric looks a little dull in the end result. It was a mid-weight cotton I’d dyed some years ago, probably with drimarene K.

indigo_01This shows a series of experiments with a pink voile (commercially dyed). A swatch of the original fabric is top right. Below that is part of a 40 cm square that was pleated and tied between two squares of thick perspex. After 5 minutes in the vat this had rich blue where the dye wasn’t resisted and a halo of off-white around the protected pink. On the left are 6 swatches. Each had a simple knot tied in the middle to provide a resist. My plan was to dip them for increasing times. My original idea of 5 minutes, 10 minutes etc was reduced, based on the earlier sample. Unfortunately I chose 30 second increments – so the samples range from 30 seconds to 3 minute dips. There is more difference in real life – trying to sort them by eye I swapped a couple, but had the general sequence right. With the glories of hindsight I wish I’d used 1 minute increments.

indigo_05I tried the same process with a yellow, heavier cotton. The 5 minute resisted sample on the lower right almost has some blue. Most of the dyed area is a sequence of greens. Once again I was able to sort the 30 second increment dip swatches by eye, but the differences were tiny. A part of that was the unevenness caused by the knot and incidental folds of the fabric, but really it was that poor choice of timing. For this heavier fabric 2 minute increments would have been better.

indigo_06It’s interesting to see the pink and yellow resisted samples side by side. There is no sign of colour mixing on the pink sample. It is indigo blue where dyed, that halo of off-white, then clear pink. The yellow has no halo, then colour mixes to green. I believe the sodium hydrosulphite in the vat, used to reduce the indigo, is the cause. That chemical can also be used to discharge – that is, intentionally remove dye colours. A discharge agent acts differently for different dye types, and even different colours within a dye type. I think the pink commercial dye was very susceptible to discharge by sodium hydrosulphite, so was completely removed where ever it was touched, even if there was insufficient indigo to leave colour. The yellow dye was much more resistant – so I got colour mixing and no discharge halo.

indigo_03My stamped linen sample was seen in an earlier post (2-Jan-2015). I had a couple of other fabric samples, nothing too exciting. Some white panne velvet ended up a very pale blue. I didn’t expect any colour at all, given it is 100% polyester. I suspect it is not at all wash-fast. My other main area of inquiry was paper, but I’m keeping that for another post. As the host of the dye day I still have the indigo vat and have been visiting it each day with experiments as part of my daily sketchbook. More on that in my next sketchbook roundup.

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January 2015

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