Indigo vat as soap colourant

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I haven't found SMF hits (prior to this thread polluting the search results) for vat-style reduced indigo as a soap colourant. This comes closest:
But 1. @penelopejane didn't add (reduced) vat directly to the soap, but oxidised to indigo proper beforehand, 2. at least for now I'm less keen on pink/purple or green from indigo, but tackling a decently vibrant blue, and 3. (and most importantly) any opportunity to show off beautiful azure/denim-coloured soaps is a good opportunity!

Some of my prior efforts around indigo: (Leuco-)Indigo and a puzzling Soap Chameleon | Infusion

Step 1: Vat
I kept things conservative and stuck to the well-tried 1-2-3 fructose vat (1 part indigo, 2 parts calcium hydroxide, 3 parts fructose), just with Ca(OH)₂ replaced by NaOH (coz soap, ye know).
For random reasons I chose woad extract (66 mg). Dispersed (inside a test tube with lid) in 4.7 g of a weak 3% NaOH lye (accounting for lye in the final lye dosage). After that I added 202 mg fructose, flooded the empty space of the test tube with butane (lighter gas, poor man's oxygen-free/inert atmosphere), and closed it airtight. Upon heating and shaking, the fructose dissolves and reduces the bluish-black powder to a red-brown solution, that looks like soy sauce/iodine tincture (for now I blaming a peculiarity of woad that the colour isn't greenish-yellow as expected from vats – or is this just a matter of concentration?):
woad_vat.jpg
Some sediment remained undissolved, but it didn't appear dark, rather greyish, so I guess it wasn't unreacted indigo, but some other impurity.

Step 2: Soapmaking
I had made an oil blend beforehand, and added some woad extract powder (1.6% TOM to be precise) to it. Cooling down while stirring kept the powder in dispersion until it was kept there by solidifying fat crystals, no sedimentation. Let it sit for three days.

On soaping day, I made two soap batters, one from the woad-infused oils, the other from the same oils but the not infused portions. I added sorbitol at 3% TOM to the woad slurry batter, and 2.6% TOM to the vat batter (to account for the 0.4% TOM of fructose in there).

When eventually reaching light-medium trace, I opened the vat vial. The orange-brown solution started turning blue literally within seconds. I was in a hurry to pour it into the soap batter, give it a short but thorough whisk, and pour it into the mould. The batter turned into a dirty green-brown colour, with a tendency to become blue at the surface, just as I'd expect it. The effective concentration was 0.13% TOM, so less than a tenth of the “wasteful” direct infusion.

Step 3: Cutting (T+18h)
T+18h_cut.jpg

OK. Let's not talk about the soap itself, I know that I'm stupid, and my superhuman talent to provoke false trace has hit me hard this time. I'm not even sure if it made through gel phase, even though I had CPOP'd it.

I had poured the woad slurry batter first, then the vat batter, and applied a simple improvised hanger swirl design. First thing to note after unpacking: The colour depth and evenness is much better than with my previous test cubes, though I haven't put in much more indigo. Letting the indigo some time to get used to its oily environment pays off. I'm particularly glad that no bleaching at the outer sides had taken place.

Then the vat chameleon. What the actual [redacted] is going on there? The top layer is snow white. Bulk is yellowish-brown and easily discolours to a cyan blue when cut open/exposed to air, so far so good and expected. But why then is the effect strongest at the bottom, in the vicinity of the woad slurry batter? And why does it seem to be boosted by stearic spots?

But that's not all…

Step 4: Planing (T+36 h)
Over night, all that olive, green, or aqua coloured zones have become white as well. Not the faintest trace of visible indigo left :(.

For several reasons, the surface needed some planing. Beneath the surface, a vibrant turquoise/azure hue appeared. Digging deeper revealed that the very inside is still at reducing conditions, i. e. yellowish and turning green within minutes when exposed to air.
T+36h_dig.jpg
Once again, the vat oxidation seems to be very picky where to happen and where not. Strongest once again close to the interface to the dark slurry zone. But the reappearance of colouration seemed to avoid the stearic-spot zones this time.

Step 5: At the sink
Thanks to the ruined oil blend/soap recipe, the soap felt quite mature already, as if it was two weeks into cure (and non-zappy), so I gave it a shot to wash my hands with it, and to erode the soap surface (the leftmost block in the upper pic).
T+36h_sink.jpg
Photographed immediately after usage; the yellow streaks have turned turquiose in the meantime (the denim blue only appears to have altered, due to lighting conditions). Just like with my (indigo carmine based) OPW soap, I'm getting the impression that there are really a lot of “surprises” hidden beneath the surface, and just wait to be rinsed away during usage!

Discussion
Under the conditions tested, indigo vat as a soap colourant has some promising/compelling sides, but is still highly unreliable. Good for surprises, at best. The bleaching on the sides is really anooying. But direct addition of reduced vat to soap batter is totally possible (though a bit of a “blind flight” since it's so hard to predict the final look).
I'm actually impressed how much colour one can get out of so little base material. I'd guess the colour depth is about half as the woad suspension, but at less than one thenth of colourant invested! It is also a smoother (no dark specks), more saturated, and brilliant colour than the slurry, though at a hue much more on the green-turquoise side.

Further directions
First and foremost I'll have to keep a close eye how these develop over time (I'll post updates here). For future trials (note to myself: use a proven and well-behaved soap recipe next time!), the concentration/proportion of vat can still be increased, I'd say threefold is very possible.

Then, I feel that the amount of fructose is very generous, since it is laid out for vat (fabric dyeing with constant air contact). Cutting down the excess of reducing agent might speed up the reappearance of the pigment and/or limit the unreliable discolouration. From naïve stoichiometry, a ratio of 1:1 (instead of 3:1 of the 1-2-3 vat recipe) might be sufficient. In the end, thanks to air-free dissolution/reduction, I don't lose any fructose to oxygen in the preparation.

On top of this, the botanical source of the indigo is a free parameter.
 

Marsi

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ive purchased woad and indigo seed to grow this season
ill join you in testing as soon as i have enough plant material

😍 your experiments
 

penelopejane

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RO if you go back to the method I used to reduce the indigo
And see great cakes soapworks experiment

I think what you have to aim for is no spots of indigo in your mix. That way the colour of your soap is a consistent blue/grey all the way through the bar.

personally I’m about to give up on indigo. I love the green of the chemically made indigo but since I’m going for natural soap I can’t use it. The grey/blue I get from organic indigo just isn’t Blue enough for me and it changes every time I use it to make soap. Sometimes is a good colour and other times it isn’t. It is effected by temperature, time of day, a breath of air and whim as far as I can see.:rolleyes:

One thing that I think does make a difference is if you use the reduced indigo made via my method on the day it’s made it is a more consistent colour.
 
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it changes every time I use it to make soap. Sometimes is a good colour and other times it isn’t. It is effected by temperature, time of day, a breath of air and whim as far as I can see.:rolleyes:

That's – kind of – my observation so far too. The rind bleaching is really weird and annoying. But what makes me optimistic is the observation of the depth of colour that stayed present for the highly concentrated woad slurry.

Your point with the specks is very valid, but difficult to avoid if one puts the indigo into the soap batter in the oxidised (coloured, insoluble, dispersed-only) state. I interpreted your “fish tank aerator pump for 30 mins” protocol that you first reduced the indigo (thiourea dioxide), but then oxidised it back to the coloured molecule prior to putting it into the soap batter. Your steps were practically a purification of the indigo, without deliberate addition of leuco-indigo into the soap batter. Did I get you right?

Neither did Amy Warden's Great Cakes Sowapworks article actively reduce the indigo to a vat in the narrower sense (try to get as little oxidised indigo into the batter as possible). Note that the commercial/chemical pre-reduced indigo is deep blue by itself, and isn't quite fully reduced for obvious reasons. There is some headspace in any case.

My vat-coloured soap is very smoothly coloured and has absolutely zero dye specks, plus that lovely intense sky-azure hue. It is less similar to pre-precipitated/dispersed/“infused” indigo, but closer to commercial pre-reduced indigo (just that mine isn't synthetic [in the petrochemical sense], but plant-based).

indigo_T+6d.jpg
This is the soap bar now (6 days old) where I've cut away the corner (in #1 “planing” photo above: the second from the left), with the whole surface freshly planed two minutes ago. I didn't see any still reduced (yellowish-olive) zones in there. Again, the vat blue had vanished along the sides, and wherever stearic spots appeared, but I'd call it promising in any case. Indigo definitely isn't something for the weaklings. I don't know yet if I am a weakling or not.
 
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Next soap, next vat, next indigo source.

With respect to the last vat (0.13% TOM woad), this is now more than double the concentration, at 0.30% TOM, and I used the añil (Guatemala indigo) instead of woad.
I also cut down the amount of fructose from 3 to 2 times the weight of indigo, and it still seems sufficient for a full vat reduction. I noticed that the añil gives a greenish-olive vat (unlike the reddish woad vat).
Another important variation is that I eventually added all the lye to the vat (30% lye concentration). Most importantly, this means that I didn't add the indigo at trace, but it was in the soap batter from the very beginning.

12 hours after making, freshly unmoulded and cut, it's still noticeably green, and somewhat dark-dirty (note that this soap, unlike the former, definitely went through very thorough gel phase):
anil_volcano_T+12h.jpg

Two hours later, the colour intensified a bit. Upon planing, some greenish core surfaces again:
anil_volcano_T+14h.jpg

I'm very happy with this one, since except for the top, it appears to be not strongly affected from rim bleaching. The colour depth is also in a sensible range, something definitely worth working with, and not as wasteful as the ordinary infusion/slurry. Compared to my 4×4 indigo cubes, it's already a much deeper and more saturated colour, at only a third of indigo PPO.
 

penelopejane

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Your point with the specks is very valid, but difficult to avoid if one puts the indigo into the soap batter in the oxidised (coloured, insoluble, dispersed-only) state. I interpreted your “fish tank aerator pump for 30 mins” protocol that you first reduced the indigo (thiourea dioxide), but then oxidised it back to the coloured molecule prior to putting it into the soap batter. Your steps were practically a purification of the indigo, without deliberate addition of leuco-indigo into the soap batter. Did I get you right?

Neither did Amy Warden's Great Cakes Sowapworks article actively reduce the indigo to a vat in the narrower sense (try to get as little oxidised indigo into the batter as possible). Note that the commercial/chemical pre-reduced indigo is deep blue by itself, and isn't quite fully reduced for obvious reasons. There is some headspace in any case.

My vat-coloured soap is very smoothly coloured and has absolutely zero dye specks, plus that lovely intense sky-azure hue. It is less similar to pre-precipitated/dispersed/“infused” indigo, but closer to commercial pre-reduced indigo (just that mine isn't synthetic [in the petrochemical sense], but plant-based).

This is the soap bar now (6 days old) where I've cut away the corner (in #1 “planing” photo above: the second from the left), with the whole surface freshly planed two minutes ago. I didn't see any still reduced (yellowish-olive) zones in there. Again, the vat blue had vanished along the sides, and wherever stearic spots appeared, but I'd call it promising in any case. Indigo definitely isn't something for the weaklings. I don't know yet if I am a weakling or not.
I strain my indigo through very fine cotton so there are no dots in the final product.
I don't know if the method I used (thiourea dioxide) actually reduces the indigo but I think it does it certainly makes it go a lot further than directly using a tsp of indigo in the mix. It is how they treat indigo before they use it to dye clothes.

I couldn't buy (at the time they didn't have it available) the really strong indigo that Great Cakes soap works used. Mine just makes blue/grey. I love the colour of the pre-reduced (synthetic chemical) indigo but I can't use it in my soap as I am going for as natural as I can.

I thought adding the indigo to lye and letting it heat up would do something but it didn't with the indigo I have.

You still have dots in the dark blue section of your soap. Is that adding indigo powder directly to the batter?

The darkest colour that doesn't run that I've got is using indigo infused oil and indigo (oxygenated by my method). I am trying to get a reliable not too dark blue - washed out denim blue.
 
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Update (age: 58 days)
woad_T+58d.jpg

The same piece of soap as in post #5.

Unfortunately, much of the brilliance after the initial oxidation has gone. The top portion is still a bit bluish, but by no means as bright as after the initial vat re-oxidation, and its originally bright aqua-blue hue has caught a more greenish-turquiose tan and lost much of its depth.
 
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